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Introduction and Noobie 3 phase wiring help?

TSims

Plastic
Joined
Oct 26, 2007
Location
Dallas, TX
Hey guys, I've been wanting to buy a mill for the shop for a long time and finally took the plundge. I feel like I got a good deal and it had the features I thought I wanted for the money I had to spend. It's a '77 Bridgeport J type 9x42 table dual powerfeeds (seller said they were servo type 150 bed feed actuator which I don't know exactly what that means?) and a Acu-Rite DRO.

I'm looking forward to learning about milling and lathe work (recently bought a small 9x40 Enco) and this seems like a great site!

First and foremost, I was hoping that someone can either point me to a previous discussion that will help me wire the mill (3 phase). Or walk me through it. I do have 3 phase service to the building.

Thanks guys!
 
I wanted to add a picture of the tag on the motor. To me this reads as 1.5hp, 3 phase either 220/230 or 440/460 volts. Is this correct?

http://www.dallas-powerhouse.com/mill.jpg

I've sorted through the breaker boxs in my shop and wired my lifts and welder plugs for 220v single phase. I also ass-umed that the 220v leg in the breaker box is in fact a 3 phase leg and you get 460 power from using both 120v legs and the 220v (120+120+220=460).
 
TSims, first and foremost verify your voltage, leg-to-leg. It is most likely to be 208, 240 or 480vac.

Next figure out how to shut the power off while you work on wiring.

The Bridgeport motor will likely be a dual voltage motor although single-voltage versions are known to exist. Assuming the dual-voltage model, you will then have to configure the wiring behind the drum switch for low or high voltage.

Normally for 480v

L1-1
L2-2
L3-3
4-7
5-8
6-9

are the connections that are made. L1, L2, and L3 denote incoming power "legs".

For low voltage:

L1-1-7
L2-2-8
L3-3-9
4-5-6

The numbered wires (1,2,3,4,5,6,7,8,9) are wires emanating from the motor and should be numbered via crimped metal band or else printed into the insulation jacketing.

There is a possibility that no re-configuration is required if it came from the same voltage service.

As always, causing the motor to reverse direction is performed by switching any pair of (L1, L2, L3)
 
You're right about the motor. You're way wrong about how you get 460- you should really have an electrician do this before you let the smoke out or much worse, get hurt.
Good luck,
 
Sure I could hire an electrician. And I've done that before. Now here I am again and I didn't learn anything. This time around I'll find a class, book, or some kind of documentation to learn how.

I understand the basics of AC and DC electrical systems. Not sure why people always discourage learning about this stuff.
 
Congrats on your new(ish) Bridgeport. You're about to enter a whole new world of learning what not to do and maybe in the process make some cool stuff. To your questions:

Uhhh nope. If yours is a residential box it's 99.999% sure of being single phase and even in Texas that means 230 Volts across the two incoming lines and 115 from each to the white neutral. It's not three phase.

You cannot run a three phase motor from single phase without an intervening gadget that makes three phase from single phase juice.

Not to worry the "gadget" is old art well understood. The gadget can take many forms. There is the static phase converter that is relatiely cheap that will get you started (so to speak. There's the rotary phase converter you can make yourself using the static converter to start it. There is the variable frequency drive (VFD) which is a box of electronics that can be used on single phase power to convert it to three phase and do other dazzling things. Then there is the Phase Perfect, another box that makes three phase power from single phase.

All have their advantages and disadvantages. You have a learning curve to climb.

Looks like the VFD phase converter forum is down because of the recent website crisis. Here's an article I wrote some time ago. In Nov/Dec 05 and Jan/Feb 06 Home shop Machinist you'll find the complete articles with photos.

Sorry about the length of this posting; there's a lot to know about induction motors and how to run them:

Here’s another huge topic to distill into practical everyday terms – induction motors. We who squander our substance equipping our shops with machine tools and machinery are often confronted with questions about the motors needed to drive them. You hit the brakes passing a favorite salvage yard where a machine only slightly rusty has been newly placed in the yard. You park, bail, and look. It’s in fair shape and almost exactly what you’re looking for but it has three phase motors? Ooo! Dang! Can I run this machine from single phase? Yes, if you’re willing to jump through a few hoops and among the hoops is the one where you need enough basic understanding of induction motors to make shrewd decisions. The object of this issue is not so much to answer your questions but to equip you with a vocabulary and background to help you phrase your questions and offer a few places to look for answers

You’ll likely find one or more induction motors in most every electrically powered machine not intended to be hand portable. There are many types of induction motors (repulsion induction, wound rotor induction, shaded pole, synchronus, hysteresis, and several others, all variations on a theme, and each having its niche of applications. While many of these exceptions are interesting to the inquiring mind, the plain vanilla everyday general purpose induction motor is our topic for this issue.

For those who have always been perplexed by electricity it’s enough to say electricity follows many of the rules for pumped water. Most every item of electrical apparatus has a plumbing equivalent. If you think about electricity in those terms - provided you don’t overdo the analogy - electrical work become simpler to think about. You will find no squiggly line diagrams in this article. For those who require deeper knowledge I refer them to the technical section of the nearest used book store for McGraw Hill “American Electrician’s Handbook” Audel’s series of electrician’s handbooks, 100 level college physics texts for EE’s, and most especially Richardson’s “Rotating Electrical Machinery and Transformer Technology.” The public library is still a gold mine of information for those with electrical questions.

An electric motor of any kind is a power conversion device. Electric power is consumed to produce mechanical power via electromagnetism. The power conversion is not 100% efficient. It’s accompanied by losses of several kinds. Regardless of these losses, induction motors are several times more efficient than internal combustion engines of equivalent power.

Induction motors are simple in concept and execution; their construction and case dimensions are highly standardized. Motor catalogs (WHAT! You don’t have an older WW Granger catalog on your shop library shelf?) have in their reference pages frame charts of the US (NEMA) and Metric (EIS) motor standards in current use. Older motors conform to older standards for which charts are still available if you look for them. The “Old Arn” enthusiasts will be dismayed to learn that the power output of a 5 HP motor made 60 years ago is the same as one made a month ago. The internationally recognized unit of HP has not changed since the days of James Watt and if you elect to use an older motor with the idea it will be more tolerant of overloading, smoke pouring out of its case will let you know how well you guessed.

There is hardly a more reliable manufactured article in the world than an induction motor when they’re operated within their ratings. I have a 1919 era motor that ran a tenoning machine in a millwork shop. It was in daily service making tenons for doors and windows until 1988 when the shop doors closed forevermore. The motor after nearly a century of operating under benign neglect still works as good as new. The message here is old motors in good condition will run as well as brand new motors – if not quite as efficiently.

Motor Anatomy: Three phase motor construction is simple. There’s a single moving part – too bad everything can’t be that simple. Open one up and you find an armature on its shaft, the stator with the windings and its base flange, a pair of bearings (usually ball), and the endbells which support the armature and bearings concentrically in the stator. Oh, and there’s a junction box (J-box is the saltier expression) where the motor leads are connected to the incoming power.

A single phase AC induction motor is more complicated because it will not self-start. They have to have a starting circuit to get them spinning. This usually consists of a centrifugal start switch mounted at one end of the armature and a capacitor in a metal housing attached to the shell of the motor. This capacitor housing is almost a dead giveaway for identifying a single phase motor from a distance.

Motor Operation: Most everything that moves requires an interaction of forces. In an induction motor the interaction of two magnetic fields produces rotary motion and thus mechanical power. They work on the same principle as when a kid uses one magnet to move another around the kitchen table using only the interaction of their fields.

Induction motors run from alternating current only; either single phase current from your residential service or three phase power where it’s available in commercial and industrial settings. They run at an RPM fixed by the design of the motor and the frequency of the power fed to them. Their speed regulation is excellent, they slow down (“slip” – remember this word) from idle RPM by only about 5% at full load. You hear “poles” when discussing motors. A magnet has two poles one North seeking and one South. Motors are wound with an even number of poles. A two pole 60 Hz motor runs at 3600 (3450 counting slip), a four pole motor at 1800 (1750 counting slip), and so on.

An induction motor is just that, a motor that works by induction according to the laws of electro-magnetism discovered by Faraday and his peers 150 years ago. The stator is a specialized electromagnet where windings of insulated copper wire are arranged in slots in the stator’s laminated iron core. The stator’s magnetic field is directed to its bore where it influences the armature. AC flowing through the stator windings produces an alternating magnetic field, which in turn induces and electrical current in the armature windings. The armature has windings of its own but the newcomer may not recognize them as such. Usually they are die cast aluminum and often have an integral fan. The alternating stator field induces an opposing current in the armature winding and the armature revolves to follow the rotating field in the stator.

Another term for induction motors is “squirrel cage”. The nature of the induction motor requires the armature winding to consist of heavy conduction bars in slots of the armature iron short circuited by heavy conductive rings on either end. Remove the iron without disturbing the winding and it does looks like the exercise wheel in a hamster habitat – a squirrel cage. The short circuit design of the squirrel cage is the single most important feature of the induction motor. The short circuit “traps” the magnetic field induced in the armature turning it into an electromagnet responsive to the rotating field in the stator.

Three Phase Power: Most industrial plant equipment is three phase for good reason: three phase power is almost universally available (except in residences). Three phase induction motors and their controls are far simpler to work with and since they have but one moving part (three phase motor self start and so avoid complexities like starting circuits), they are much more reliable.

Three phase AC power is transmitted by means of three conductors. Each pair of conductors represents a single phase circuit. The “three phase” comes from the timing of the three circuits. Each circuit is 1/3 of a cycle out of phase with the next. This phase relationship rotates. When three phase power is connected to the windings of the motor it results in a smoothly rotating magnetic field that drags the armature along with it. Three phase motors are famous for their simplicity, durability, and smoothness of operation. I’ve seen three phase motors especially modified for use on our Navy’s submarines; they are so quiet they literally cannot be heard in operation - even in a quiet room.

Motor Nameplate: The motor’s nameplate is where all the relevant motor characteristics are recorded and permanently attached to the motor. The nameplate is so important to the end user I’d recommend against accepting a free motor whose nameplate is missing. The nameplate and the information on it is required by whatever national standards organization or insurance underwriters testing facility having authority in the country of origin. In the US its NEMA (National Association of Electrical Manufacturers) and UL (Underwriter’s Laboratory.) Until recently the nameplate had to be etched metal with the ratings stamped into the relevant fields. With the advent of tough plastics and catalyzed printing inks this requirement has been modified. However, when dealing with them it should be remembered that overzealous cleaning may remove the all-important information.

Lets look at the many fields of information on a typical nameplate.
- Manufacturer’s name, motor’s model, and serial number: Self explanitory.
- HP: actual rated continuous mechanical power output at the rated electrical input, temperature rise, and duty cycle.
- Volts: the motor may be connectable for dual voltage 115/230 or 230/460 for example. NEMA rated motors are required to accommodate +/- 10% of their nameplate rated voltage.
- Amps: here again the dual voltage may require two figures 12.6/6.3 for example. The lower voltage requires higher current to develop its full mechanical output.
- Hz: the line frequency in cycles per second
- RPM: the motor’s rated RPM at full rated load. Motors operate at some multiple of the line frequency. Here in 60 Hz USA induction motor’s no-slip synchronus RPM’s are 3600, 1800, 1200, 600 etc depending on the number of poles. Slip at full load reduce this to roughly 95% of the synchronus RPM. 3450, 1750 etc are common.
- SF or Service factor: This is 1.0 or greater representing the amount of excess capacity over ratings the motor will tolerate. A light duty motor running a home shop drill press for example could be 1.0 SF; a heavy duty motor selected for a rock crusher might well be 1.15 SF.
- Duty cycle: seldom seen these days but it represents the permissible percentage of time at full load
- Temperature rise: All motor generate heat. The temp rise indicates the amount of temperature increase the motor uses to dissipate its normal heat load.
- Insulation class: So far motor insulation classes run A through F. These classes have nothing to do with the quality or the types of insulation materials. It only represents the maximum temperature the insulation will withstand.
- Frame: Motors are built to standards so they are interchangeable. The mounting holes, shaft size etc are all the same regardless of manufacture. A new 3 HP 184 frame motor from Baldor will directly replace a 3 HP 184 frame motor made 30 years ago by Century, Lincoln, or Louis Allis.
- Connection diagram. Many motors are dual and sometimes triple voltage. The surest way to fry them is to connect them improperly. The connection diagram has that information. Inside the motor’s junction box are the leads for the motors windings. These are connected in series or parallel to match the motor to the line voltage.

Motor Leads: On the leads are metal tags, bands, for lead identification, or the numbers may be embossed in the wire itself: T1, T2 and so on. Some three phase motors might have as many as twelve leads. While there are a limited number of ways to connect them the consequences of connecting them improperly may result in permanent damage to the motor so I’m not touching that hot potato except to point it out in loud clear terms. If you’re uncertain how to re-connect a motor take your problem to a motor shop.

Motor leads on single phase motors can be more difficult. If you lose the connection diagram you’re not quite sunk but you might as well be. There’s no consistent color code or connection arrangement for single phase motors particularly older motors. Better get some help from the motor shop hooking them up and making out a new connection diagram. I do and I’m alleged to be electrically smart.

Older motors leads can be so friable they crumble like saltine crackers when handled. The usual fix is to slip two layers of shrink tubing over them. If the lead number or tag is lost it’s a motor shop job to trace out each lead pair wire by wire and with a cheap compass and a low voltage battery determine their polarity.

Motor Resources: This takes us to an important man to a home shop machinist, the local motor technician. It’s in the nature of things that motor shops are still small mom and pop businesses resisting the franchising characterizing today’s economy. Your local motor guy can help you diagnose motor problems and identify wires, chase down and restore brittle leads broken off at the winding, bake and dip stators, and perform all kinds of salvage services for not that much money and his advise is indispensable. My local motor guy is featured in a few of the accompanying photos. He’s typical of the breed; learn to recognise them.

Enclosure: Motors can be open drip proof (ODP), totally enclosed fan cooled (TECF), totally enclosed non-ventilated (TENV,) explosion proof, and so on. These enclosures are indicated by letter designators by the manufacturer. ODP and TEFC are the designators of most concern to the home shop machinist. ODP motors circulate outside air through the motor to cool the windings and are best employed in sheltered environments away from conductive dusts and drifting mists. ODP motors tend to be lighter and lower in cost. TEFC motors are fully enclosed against outside air and contaminants cannot intrude into the internals. They can be mounted anywhere provided their fans and shrouds are not obstructed from free air flow.

Shaft: The business end of the motor is the shaft where pulleys and mechanical loads are connected. These are also standardized with the frame designator, are keyed, and usually made of plain barstock. Motors have few “handles” and can easily be dropped so their shafts are involved. This almost certainly results in a bent shaft. Here is a question that frequently comes up: I have a new motor and an old pulley. The pulley bore is too small. Can I turn down the shaft to fit? I always advise no. Never modify a motor (or any other standard off the shelf item) if you can possibly avoid it. You might have to replace the motor and you’ll have to modify another shaft.

Re-powering Machines: This refers to installing larger or smaller motors, converting from single to three phase, or consolidating the machine’s drive from multiple motor to one or the other way around. Even changing out a ½ HP three phase motor on a 10” South Bend lathe for a single phase motor has its technical considerations and an analytical, engineering approach is highly recommended. These are important issues when selecting control components. I cannot cover even one example of re-powering a specific machine tool in the 6 or 7 pages allowed me. The best I can do is offer the basics and encourage the home shop machinist to work out all the details before starting and to seek sage advice early in the game.

HP Vs Watts: People often refer to the HP to Watts conversion factor when discussing motors. This is where theory and reality combine to form a trap. If you have faith in the 746 Watts = I HP remember that it’s a theoretical equivalent – it presumes a perfect motor. This formula neglects at least two items of technical concern when calculating motor Amps - like actual nameplate full load motor current and starting surge.

My Baldor catalog lists several 1 HP single phase general-purpose induction motors. Their rated FLA (full load Amps) is 12.8 to 13.6 Amps when connected for 115 Volts NOT 6.5 Amps as would be indicated by a blind acceptance of the HP to Watts conversion formula. One's first point of reference in selecting motor control and protection devices is the motor's nameplate where its electrical ratings are permanently stamped into metal.

Starting Surge: The other point I mentioned is starting surge which can be 4 to 5 time the motor's rated FLA on single phase motors (more for three phase). This surge lasts but a few milliseconds (depending on load inertia) and rapidly dwindles to idle current as the motor accelerates to full RPM's. The surge is over so quick the fuse or circuit breaker hasn’t time to heat up in response.

It’s the starting surge the contacts of the motor control device sees at every start whether the device is a cheap switch or a NEMA rated motor starter. Therefore the motor control device has to be robust enough to take repeated motor start/stop cycles; thus the need for "motor rated" switches featuring larger contacts and inductive load breaking capacity. These features endure long reliable service life for the motor control device and thus justifies its higher price.

Motor Control: Controlling a motor can mean simply turning it on or off with a switch to the most elaborate electronic controls. Controlling a motor with a switch has its hazards. For one thing it offers no over-current protection. For another if the power fails and the machine is left “on” and unattended, restoration of the power results in an “unattended start” always a dangerous situation to the equipment and to anyone working on the equipment. For that reason, the National Electrical Code requires any motor operated item of equipment to automatically disconnect its load from the line in case of a power failure. It also requires a lock-out on the machine’s electrical control panel or a lockable power disconnect within sight of the equipment. While this might seem overkill for a 7” shaper it’s never the less an NEC requirement for electrically powered industrial equipment.

Motor protection: Motors have to have some kind of motor over-current protection. This can take the form of fuses, molded case circuit breakers or the safeguards found on electronic motor controls. Properly selected motor protection has a built-in delay to accommodate starting surges and momentary overloads. There are fuses of several categories and breakers specifically rated for motors. Overload relays that are part of magnetic starters, switches with thermal trips, “Fusetron” arrangements, and other devices are all designed to protect your motor from frying. Most home shop equipment are pampered pets; they live a life of ease and luxury, seldom worked to capacity. Thus the usual home shop while filled with electrically powered equipment seldom suffers electrical casualty. It’s simply never worked to capacity.

The wiring and other considerations are subject to the National Electrical Code and your local code. I caution every-one of the hazards associated with getting electrical advice from competent-sounding buddies at your favorite on-line bulletin boards. They may or may not know what they are talking about when it comes to electricity. The chances of electrical shock or fire are vanishingly remote for a properly installed electrical hook-up for an electric motor in otherwise good shape but the chances compound for every corner cut in its installation or wiring. Another point is that fire marshals are specialized detectives who are very good at investigating fire damage. If you suffer a loss fire the marshal’s report goes to your insurance company. If it develops that the fire originated with owner installed substandard wiring or improper circuit protecting devices then, depending on how the policy is written they could elect to decline paying damages. Your local electrical code supersedes the NEC so be sure your work complies – or if you hire any electrical work that it’s up to standard and not a lick and a promise job no homeowner could get away with.

Reversing: Once upon a time when motor manufacturers offered real engineering data in their catalogs they included among other things curves representing the number of times their motors could be plug reversed under different conditions of connected inertia. I recall that a 5 HP 1750 RPM three phase induction motor with no inertia load but that of its own armature could be plug reversed across the line 30 times a minute and still stay within its thermal ratings.

"Plug reversing" means applying reverse power to a motor already running at full forward RPM to full RPM in reverse. A "plug stop" means reversing the motor only until it comes to a stop at which time the power is automatically (or manually) shut off. Three phase motors may be plug stopped or plug reversed with little concern for heating but then you have to consider the inertia load and the number of times per minute you do it. Tapping holes in a drill press might require 10 cycles of plug reversing then there will be a period when you have to drill another hole,. change the set-up etc when the motor can shed its excess heat.

Most single phase motors cannot be plug reversed. If you try the motor will keep going the same direction. It’s the starter circuit that gives the single phase motor its initial direction. If you absolutely positively have to have a reversible motor there’s no solution except to replace it for a motor that will electrically reverse.

Single Phase Troubles: Those of you who have bought small lathes equipped with single phase motors or if you converted a three phase machine to single phase by replacing the existing motor with a single phase unit, you may have encountered a finish problem. If the feed marks are closely examined they seem to resemble the grooves in an old fashioned record, that is they may have varying depth or an irregular appearance much like chatter. Extreme cases may look like hell.

It's sometime difficult to distinguish this problem from another - tool chatter. If the finish problems cannot be eliminated by the usual chatter remedies, you might be troubled by motor vibration "phonographing" the finish.

The problem may be caused by a torsional vibration in the single phase motor, sometimes called "cogging." The armature of a motor is tightly gripped by the magnetic fields that cause it to rotate. A single phase motor acts something like a single cylinder engine where the power pulses may be several times the average torque of the full revolution. This pulse is transmitted by the belt to the spindle and the opposing torque transmitted by the motor stator to the machine. The consequent vibrations may meet where the tool contacts the work, recording itself on the finish like music on a phonograph record.

Here's a trouble-shooting method: Slack the belts so they will barely drive the lathe while it's in a light cut. If possible, isolate the motor by slacking off the mounting bolts and slipping hose washers between the motor base and the mount and between the bolt head and whatever it bears against. Tighten the bolts just enough to hold the motor in position. The object is to inject as much compliance and damping as possible in what is usually a rigid drive. If things wobble around a little it's OK. That's our plan. Take a couple of trial cuts and see if there's a significant improvement in the finish quality. This suggestion is intended to support diagnosis not a fix.

If the pattern disappears when the machine is practically de-coupled from its motor, that indicates the problem is definitely motor, not belts or tool chatter.

The only solutions are to either to de-couple the motor via rubber motor mounts or procure a new motor smoother in operating characteristics. Often, there is something about in a lathe/bench assembly that propagates motor vibration. You might try placing sandbags here and there on your lathe bench or motor mount. Inert weight like sand or pea gravel blots up vibration to an amazing degree. If sandbags cure the problem, chances are the bench or whatever needs stiffening or reinforcement at those points.

If your checkbook can stand it, a new motor might be the best solution because you can upgrade in power at the same time -- that is if your electrical system can stand the extra load.

The best solution is naturally expensive: either a DC motor and solid state drive or a 3 phase motor preferably with a solid state drive if not a rotary phase converter.

I also suggest a softer acting V-belt known as "Link Belt." This is a V-belt comprised of interlocked rubber/fabric links. Links can be added or removed to secure the desired length. Their principal advantage is their forgiving nature and vibration mitigation. Another big advantage is you won't have to dismantle your spindle to replace the V-belt, just cut the old belt off and link together the new belt.

Needless to say, the smoother the drive the better. When I bought my lathe new in 1971, it came direct driven by a 3 phase motor but I replaced the motor with a 5 HP single phase to suit my power. I had the same perplexing "phonographing" problem. I solved it after a fashion by relocating the motor from the machine to the floor nearby using a V-belt drive to connect it to the head stock transmission.

A few years ago, I upgraded my lathe motor to 10 HP 3 Phase with a variable frequency drive. The motor happened to be precision balanced but I don't think that was a factor in performance improvement. It made an incredible difference not to have the 60 Hz torsional impulse or cogging. Where I used to see faint ripples in a cold drink set on the headstock, the machine now runs dead smooth. Where the gear noise used to be annoying, it's now a smooth musical whir.
If anything, I now get better finishes with my machine than on superior lathes like the Monarch1760, thanks to a smooth drive free from torque impulse and vibration.

A cautionary note. A 3 phase motor running on a static converter still develops significant torsional vibration and about half its rated HP. It will run smoother on a rotary phase converter and develop almost full HP. Therefore I suggest if you wish to change out single phase motors you obtain two three phase motors. One to run your lathe and another the next nominal HP larger from which to build a phase converter. I'd really like to suggest an electronic variable speed drive but that might be too expensive for most people.

I'm not trying to chivvy anyone into changing out motors. I'm just making owners of new engine lathes driven with single phase motors aware that there may be one more hitch in their final commissioning, what causes it, and ways to fix it.

Budget Conversions for Small Machine tools: Here in blubbery USA there's a large market in exercise machines. Naturally, they are seldom used and may be bought cheap at yard sales. They have smooth running 1 HP DC motors with a cheap variable speed drive that might be suited for your lathe or mill provided it’s used exclusively for light work or for very small lathes like 6" and under. Some of these motors feature wide-open construction and need to be protected from ships and dirt.

BTW, 1 1/2 HP is about as big as you can run from 115 Volts wall outlet (a NEMA 5-15 receptacle for those in the know). If it will fit your budget and your shop's electrical service, get a 1 1/2 HP motor.

Cleaning and Maintenance: Open drip-proof (ODP) motors will trap anything in the air blowing through them. Some may be impacted solid with dust or lint. If you bring home a junk motor be sure to open it up and check it out. Usually this involves removing the long screws that sandwich the stator between the endbells, tapping the shaft endbell loose and slipping it off the bearing. Maybe the armature will come with it. If the motor is single-phase be careful when removing the other endbell because the starter switch is usually attached to it. Proceed with care because on older motors the lead insulation can be friable. Vacuum (do not blow) out dust and dirt accumulations. Loosen caked debris using an old paintbrush or a softwood stick.

A motor stator that’s wet from a flood or that’s been out in the weather may be OK once its flushed out with fresh water and dried out. Never connect a wet motor to power. I’ve dried wet neglected motors. I remember opening one to replace the bearings and discovered stinky dead pollywogs and moss inside. 48 hours of 140 degree heat will dry the wettest motor. Many times, a workmanlike job of extemporizing a motor oven, from house insulation, a fan, a kitchen range element running from 115 volts, and a thermostatic control from an old crock pot has saved the day under a roof leak. I’ve dried motors with the DC from welding machines, kitchen ovens (on WARM!), a solar tent, and home space heaters and tarps. How you get the motor dry is a matter of ingenuity for the budget minded or the motor repair shop if you can spare the money.

Regardless, if you suspect the motor is wet, you can’t take chances. You need to check the motor with a “megger.” A megger is a hand cranked gadget that imposes a high voltage to detect leakage current, Wet or dry seeming electrical apparatus will betray its moisture through a low megger reading. Few home shop people have them but your local motor shop will help you. Mine is a cheap Asian version bought off eBay.

Bearings are a whole topic I will cover in a later issue. Here are a few tips in the meantime. Modern ball bearings furnished with motors made since 1960 or so need no attention. They are lubricated for life. That said, it’s possible over a few years for absorbent dust accumulations to wick the oil out of the bearing grease leaving behind the soap. Thus an owner of wood shop equipment has to be vigilant but a home shop machinist can skate to a greater extent. The dust is different.

When failed ball bearings are noisy and lumpy feeling. Replacing them is a simple bench mechanic’s job needing only a puller, a few wrenches and a source of mild heat to 300 degrees F.

Bushings require oil and sometime replacement. Keep the reservoirs full of clean machine oil and any felt wicking in good shape.

Older motors may be equipped with an oil ring, a loose ring of small cross section that bears directly on the shaft through a slot built right in the bearing. The ring is rotated by the shaft. As it rotates it brings up oil from the reservoir applying it to the shaft. It’s a clever solution but now obsolete.

Phase converters and variable frequency drives: (VFD) are among the topics for next month. I can comment that static and rotary phase converters (RPC) are a home shop machine’s dream once they’re working. With them a three-phase machine tool can be run on single phase power. A VFD gives you all that a rotary phase converter can offer plus full rated HP, greater electrical efficiency, and variable induction motor shaft RPM (an impossible dream only a few years ago.) All that glisters is not gold, however. Each of these clever devices has built in limitations.

Motor failures: Motors suffer several failure modes. Burning out from over-load or internal short is one. They smoke and stink like burnt toast. There’s no mistaking it. A fried motor may not be permanently harmed but that’s a call the motor shop has to make. Another failure is an open lead. It may be failed starter contact or a loose wire nut in the J box. The motor hums but won’t start. If you push the button and you hear a click and a hum but no rotation shut it off immediately. Single phase motors fail to start from bad capacities or less frequently a failed start switch. A bad capacitor is an easy swap-out; well within the scope of the experienced amateur provide the safety rules are followed. Once is a great while a starter switch may fail closed leaving the started windings in the circuit. Since these windings are intended for momentary use they will soon overheat if left in the circuit for more than a few seconds. If your single phase motor starts and hums louder than you’re used to it could be that you have a start switch failed closed. A smell of hot insulation will soon confirm it.

Summing up: Once selected and installed induction motors can be pretty much relegated to your annual shop maintenance list. My article for the next issue is AC motor control where we get into switches, motor starters, phase converters, and variable frequency drives.

Last issue we discussed induction motors in general terms. In this issue we learn something about controlling them. Caution: many electrical details presented here are deliberately simplified for better understanding. Electrical experts discovering pet peeves will have to gnash their teeth. This material is not written for them. It’s written for those who still regard electrical apparatus as containers for smoke and to whom smoke indicates a failure of the apparatus from which it emerged.

I presume the New Hand is familiar with basic electrical terms – Volts, Amps, etc and the functions of electrical control devices such as switches, fuses, and circuit breakers. From this we will start a vocabulary and a set of basic motor control concepts from which the New Hand can speak with the beginnings of understanding to technicians and professionals regarding their particular motor control requirements and to clearly articulate their problems as they occur.

Remember to do all your electrical research before you do anything you may want to undo. A home shop machinist thinking of electrical improvements to his shop should first make a browse through the DIY book section of the local big box store to find a how-to book on home electrical work. Few of these books go into detail on the connection of industrial equipment to a residential electrical system.

However, if you consider that your shop could benefit from its own dedicated panel you’ll find that most of these DYI electrical books will discuss adding circuits and sub-panels. Most of these stores also hire retired or disabled electricians who can set your feet on the path once you’ve acquainted them with your problem and plans.

Motors convert electric power to mechanical motion. We have the motor. Now some means of controlling the motor at the will of the operator is necessary. Induction motors run only at or very near their rated RPM because their RPM’s are dictated by the line frequency. They are either on or off when “run across the line” as is said of motors connected directly to the incoming power (we now have options besides on at full speed or off but we’ll discuss that later.) The motor may be controlled electrically with a switch, starter, or electronic drive. The load may be also engaged or disengaged from a continuously running motor with a clutch at the output. The simplest control is a manual switch placed in the electrical conductors feeding the motor. Close the switch to complete the electrical circuit and the motor turns on and the shaft rotates taking the connected mechanical load with it. Open the switch to…etc turns the motor off and the load casts to a stop.

The problem with this simple control is there is no protection for the motor. If the motor is mechanically overloaded it may overheat and burn up possibly causing a fire or some electrical casualty. Many small appliance motors (like washing machines, garbage disposals, and dishwashers) run very satisfactorily and safely with only a simple on/off switch. They may be adequately protected by the branch circuit fuse or circuit breaker or perhaps there is a thermal snap-action switch that breaks the circuit if the motor should overheat. Generally, the larger the motor the greater the necessity for safeguards built into the motor’s electrical control.

Lets look at the control requirements of an induction motor. First, induction motors characteristically start with a current surge many times larger than the motor’s nameplate full load Amps (FLA). Second, the motor needs some form of over-current protection. Third, if the motor is running and the power fails for some reason, you want the motor control to automatically open the circuit. You do not want the motor to restart when the power is restored (called variously an unattended or unintended re-start). Fourth is when the motor is disconnected from the electrical power there should be no motor leads remaining above ground potential. Fifth is the motor shall be connected and grounded in accordance with the National Electrical Code (NEC) and the provisions of the local code which are frequently more stringent than the NEC.

Home shop machinists live at the interface of small “appliance sized” motors powering the bench grinder or the drill press and the larger machine tool motors for which more elaborate controls may be desired. The electrical system for a turret mill or a small lathe is usually very simple requiring only forward (FWD) stop (STOP) and reverse (REV) switch in some form. My turret mill came equipped with such a switch built right into the motor housing which I used for many years. My lathe came with a more elaborate electrical system consisting of a reversing starter whose coils were energized by a pilot switch actuated by a control level on the apron.

The shops of home machinists usually begin in some cramped inappropriate space like in the garage in front of the smaller car or a damp bay in the basement. Usually these spaces start with a single 115 Volt outlet and a flourescent fixture too far away. Over time, the home shop machinist remedies these problems with a 230 volt branch circuit feeding a shop electrical panel and the installation of adequate lighting. If these improvements are up to Code there’s no reason why any machine tool cannot be brought in and connected provided there is physical space, SWMBO approves, and the electrical needs can be satisfied.

Before the turn of the 20th century electrical power was new, untested, and unregulated. Many fires and deaths were attributed to electrical failures. The safeguards we take for granted today were almost unknown. This slice of electrical history is interesting but beyond our scope to explore further. What arose from the ashes, so to speak, is the Underwriter’s Laboratories (UL), CU, the National Electrical Code (NEC) and equivalent institutions in every other country having an electrical grid and an insurance industry. Every item of electrical apparatus sold in the US from a child’s night light to the largest electrical apparatus is submitted for testing and approval for service by the UL. The UL’s approved service conditions are spelled out on the equipment itself. These nameplates and labels should never be removed, damaged, or obliterated.

Shock and electrocution is always waiting to zap the unwary. For that reason perform all work on equipment that is not only de-energized but ensure yourself that it is indeed de-energized in two locations and those are either locked or tagged out in some prominent NEC approved fashion. Any electrical supply house or big box store will sell you the tags.

Don’t ever think that because you are “grounded” (or not grounded) you can’t receive a shock or get electrocuted. All you have to do is become part of an electrical circuit and a surprisingly small current can knock you flat on your butt.

Let’s look at some switch types. Toggle switches such as manual wall switches used for residential lighting control may be used for small induction motors but the motor’s starting surge will eventually degrade them sometimes welding the switch’s contacts into the closed position (fail closed). A motor that cannot be stopped can be dangerous to the equipment it’s powering and whoever is running it.

Every switch has permanently marked on it the maximum Volts and Amps it’s approved for and sometimes the motor size in HP it’s approved to control. Motor rated switches should be used to operate motors. They have the snap action contacts and the surge capacity for motor starting.

Manual switches used to control motors run from single phase 115 Volts should break the line (hot, that is not the neutral) conductor(s). Switches used to control motors connected to 230 Volt single phase should be double pole and arranged to break both line conductors. Switches used to control three phase motors should break all three conductors. Thus no motor leads are left energized above ground potential when the switch is in the off position. No motor switch should be installed without some over-current protection such as an arrangement consisting of a dedicated fuse, or a fused disconnect or circuit breaker. Manual switches include toggle switches in their various forms, drum controllers, and some antiques now seen only in Frankenstein movies.

Manual motor starters have a built-in current limiting device usually in the form of a thermally tripped circuit breaker. Pressing the Start button closes spring loaded contacts. Pressing Stop releases the contacts which snap open quickly because of the spring charged by pressing Start. The thermally tripped built in breaker also triggers the Stop contacts and depending on how the manual breaker is constructed the motor cannot be re-started until a “reset” button is pressed. Motor load current flows through calibrated heating elements that in one of a half dozen ways trips the overload mechanism. It may take several minutes for the trip mechanism to cool before the reset becomes effective.

A contactor is a relay; an electrically operated device that uses a low power circuit to energize an electromagnet that closes contacts that makes a larger circuit. “Contactor” used in this context implies a specialized relay intended for large currents and voltages, that is, much larger than control circuits. There are contactors in production intended to control motors to 10,000 HP and more but most of us will deal with those intended for 20 HP and less.

An electro-magnetic motor starter is exactly that. It’s a contactor and an overload relay combined on a single frame specifically intended to start electric motors. They come furnished with auxiliary contacts for holding circuits, pre-wiring, interlocks in the case of reversing contactors, and other electrical expedients to be discussed later.

Push button control station. This is where the operator pokes the buttons that makes the motor do its stuff. A control station can range between a simple pair of “on/off” buttons in a flush mount box to many square feet of controls, annunciators, flashing lights, and monitors.

An overload relay is a special form of relay that opens pilot (low current control voltage) contacts if the motor current exceeds a certain time dependent value. Overload relays have a current sensing feature that usually function by resistive heating of an element that trips the spring-loaded pilot contacts open. When the overload “trips” the contacts stay open disabling the starter requiring the operator or the maintenance electrician to depress a “reset” button to close them and re-arm the spring. Only then can the motor be re-started. Thus it is protected from over-current and consequent overheating. What about the starting surge? What in deed? Fuses, circuit breakers, and overload relays all come with options allowing the electrician or EE to select a motor protective device with a “trip curve” appropriate to the motor’s starting characteristics and its service.

Reversing. Motors frequently have to be reversed for tapping, threading bores on a lathe, and so on. Thus the switches or starters and controls have to be arranged for reversing the motor. If AC can be said to have polarity reversing all three phase motors may be accomplished by exchanging the line connections of two motor leads. Single phase motors are reversed by the exchange of the two starting circuit leads with respect to the running circuit leads according to the motor’s connection diagram.

Switch reversing may be accomplished with a switch where a double pole double throw switch is used for the actual reversal connections and the motor is started and stopped with a separate switch.

If it’s req uired that a reversing and starting be combined in a single switch it’s necessary for the switch to have a three pole (three phase and 115 V single phase) or four pole (single phase 230 V) double-throw center-off configuration. Motors 5 HP and less can also be controlled forward and reverse this way using a drum controller by following the connection diagram included with the device.

A further discussion of typical motor connections and reversal diagrams may be found at http://www.metalwebnews.com/howto/elec-mtr/elec-mtr.html. I can’t vouch for the accuracy or suitability of the material found on this web site but it is informative.

Three phase motor starters for machine tools motor are frequently “reversing” that is they consist of two contactors and an overload relay. The contactors come already wired from the factory to reverse two of the motor leads and furnished with a mechanical interlock and exclusive “or” auxiliary contactss that make it mechanically and electrically impossible to close both sets of load contacts.

Here’s some more vocabulary.

Conductors. In the meaning of the NEC and technical language used by EE’s and electricians, conductors are insulated electrical wire regardless of purpose.

Control circuit. Control circuits are low current (often low voltage too) circuits used only to energize the control pushbuttons and the solenoids of motor starters etc. It also includes limit switches, emergency stop (E-stop) pushbuttons, pressure switches and all the rest of an electrical system not actually carrying load current. Control conductors are – well – the conductors that interconnect the control devices.

Load conductors. These are the conductors actually carrying electrical power to the motors, heaters, whatever. They are sized to suit the load current and the service conditions.

Ampacity is the ability of the conductor to carry current under specific conditions without over heating or causing significant voltage drop. The ampacity of a given conductor goes down with enclosure where resistive heating may be significant (in conduit, concealed within walls etc) and up with the temperature rating of the insulation. There are dozens of ampacity tables in the NEC and it can be confusing to select just which table or use to select conductors for your application. For that reason I strongly urge the New Hand to seek sage council from electrical experts when these decisions have to be made.

Resistance. Just as all structure is made of rubber every electrical circuit is a heat dissipating resistor. Conductors and control arrangements are selected on the basis of reducing heat built up in enclosed spaces as well as keeping voltage drops within reason. You may have heard of Ohm’s Law which related Volts to Amps to resistance in Ohms. I refer you to any standard book on basic electricity for a more complete discussion of basic electrical units; a discussion that is beyond our scope here. While you’re at it look up “reactance,” “inductance,” and “capacitance.” Set aside some time for these three topic words will take you a month of evening study to absorb from scratch.

Insulation. Conductors are insulated to – keep the smoke in? That’s one way of looking at it. They’re insulated to isolate one from another and to ground. Insulation is rated for voltage and temperature. Here again the NEC has much to say on insulation strength and temperature ratings for different applications. If you contemplating some DYI electrical work sure you select the type insulation best suited for your application.

Cord connected equipment. Most of us have “cord connected” portable equipment. The power cord stock suited for this service may have several ratings: “SO,” “SEO,” and so on. This alludes to the ability for the cord to withstand abuse – forklifts and other wheeled traffic driving over it for example. Contractor cord - the colorful (orange r yellow, other colors in season) vinyl stuff – is not suited for any service where hot chips or sharp chips and foot traffic are involved. The hot chips may melt into contact with the conductors and so will foot traffic tromp metal chips into the soft plastic.

Most of us have single phase shops but would like to be able to run three phase equipment. This brings us to phase converters. There are now three basic types: static, rotary, and electronic. The essence of three phase power was described in the last issue of HSM. Three phase motors require three phase power to run them. Connect a three phase motor to single phase power and it will just sit there and either blow a fuse or hum soon followed by the smoke. Most likely it won’t even try to spin. You need three phase power or something close to make three phase motor run properly.

The simplest and lowest first cost solution is a static phase converter. This is nothing more than a capacitor and a potential relay comprising a starter circuit. It uses the third leg of the three phase motor as a starting coil. Once started the static converter disconnect and the three phase motor runs quite well from single phase and it will develop about 1/3 to ½ its rated mechanical power before it slips out of sync and delivered torque and motor RPM drops where the static converter kicks in.

A rotary phase converter consists of a three phase motor and some means of starting it be it a rope and pulley or a well designed static converter automatic start circuit. Single-phase power is supplied to two legs of the motor leads and the “generated” leg is drawn from the third. In its most basic for the rotary phase converter has a weak generated leg that may be improved by adding carefully selected “balancing capacitors.” Many clever people have brought the home brew rotary phase converter to a high degree of refinement and their websites are many. Those with a need for three-phase power from a single phase source can build their own but those who have money to spend can get a factory made rotary phase converter that’s even more refined and the weak leg problem hardly affects the connected load.

The problem with rotary phase converters is while you can run multiple machines from it, machine with complex electronics will run poorly or not at all if the controls, computers or some other critical single phase loads a connected with the weak generated leg.

Phase converters are an ideal project for electrical tinkers. Once built they will give good (if inefficient) service for many years. I’ve built them as small as ¾ HP and large as 50 HP. I think that ideally a rotary phase converter should be sized about 1 ½ times the largest connected motor.

The ultimate and most expensive solution for the three phase power from single phase problem is easily the electronic phase converter. This clever gadget takes line power and from it creates the third leg through PWM technology. It’s timing and waveform are accurate and the full nameplate ratings of the motor can be realized. I understand complex CNC Machine tools may be connected to the electronic phase converter without regard to line legs and generated legs. Hook it up and start to work.

Finally we come to the “variable frequency drive” (VFD). There’s a lot to learn when it comes to making shrewd decisions regarding VFD’s Few home shop machinists have experience with heavy duty industrial electronics. The key to learning new things is to connect the basic concepts to a vocabulary. It’s no different than learning tennis or machine work than when learning enough about electricity to make a decision about VFD's. and whether they will help you with powering your three phase motor. Be patient. The learning doesn't happen overnight. The understanding will come if you apply yourself.

The speed of an induction motor is controlled by the frequency of the AC power feeding it. When plugged in the wall induction motors run only at designed speed.

Variable frequency drives are a box of solid state electronics that converts three phase (and if de-rated 1/3, single phase although some work to full ratings on single phase) 60 Hz AC to variable frequency three phase. This allows you to operate a three phase (and three phase only) induction motor at any RPM you set. The motor runs at full torque to 60 HZ and drops off in proportion above 60 Hz. They are very simple for ordinary home shop machnists to work with if you can follow instructions when setting them up.

The VFD goes between the power and the motor. On the box are some control push buttons including the "start" and "stop" button. There is also a means to increase and decrease the speed of the motor - usually a knob like the volume control of an older radio. The initial connection amounts to hooking up five wires and a ground. Inside the box are terminals for connecting it to a more convenient arrangement of external push-button controls (the original control buttons furnished with you machine if you like) but you can also run it from the push buttons on the box.

A manual should come with your VFD should you make the plunge. Do not buy any VFD that does not come with a manual. If you're electrically challenged you won't decipher the manual overnight. You'll have to study it, taking in bit at a time like you'd eat an elephant.

As for cost, $200 (used price for a pre-owned 2 HP single phase rated unit) doesn't seem expensive to me for such a talented box. It will power (separately by means of a receptacle on the VFD and a plug for each three phase motor) other three phase motors should you mount them on your drill press, lathe, mill, etc. That smooth, quiet, three phase power and variable speed adds a lot of functionality to a machine shop, and the gadget has built in economizer circuitry that will lower you power bill a tad.

Be sure to get all the manuals that go with them. There's up to a hundred settings (parameters) you set to customize it to suit your motor and application including maximum current, acceleration and a deceleration, stall prevention, and lots of other features. You can run a 1/4 HP motor from a 10 HP drive if you wish but that's stretching it.

There are many drive brands Yaskawa, Hitachi, Mitsubishi, Baldor, GE, Teco to mention only a few. Don't rush off and buy one over the counter from a retail dealer. First determine your needs, then check around your local big city mechanical drives or electric motor suppliers. Ask for take-off or trade-ins. You may be able to get last year's drive for 1/2 price. Be sure to get a 230 Volt drive preferably one suited for single input although a 3 phase only drive will work on single phase if appropriately de-rated as mentioned earlier. If you screw up and get a 460 volt VFD there's no solution but a step up transformer.

Some drives will step up 115 volt to 230 volts internally up to 1 HP. This is a drive targeted at consumers with a bad home shop habit and no way to get 230 volts in their shops. They are pricier than 230 or 460 volt drives. If you’re looking at 115 Volt VFD’s and wondering how they will work on a 5 HP motor maybe it would be a good time to run in a 230 volt service to your shop.

Used later model VFD's from the internet auction site may be quite acceptable. Beware of older technology units not because they function poorly but because they can be noisy and emit an aduible squeal that even I can hear. eBay usually has two pages of VFD's. Select "Business and Industry as a category and key in "VFD", "inverter drive", or "AC drive" as search objects.

Here are a couple of on-line sources. Once you get comfortable with the concepts of VFD technology and feel like shopping, phone them and dicker. Check out http://www.dealerselectric.com/ . Go to "Browse our inventory" then click on "inverter drives." Another one is at http://vfds.com/vfdprice.htm#120 Volt Models. These people (ant many others sell 120 volt input drives. They have a step-up circuit inside that lets them run 230 volt motors. These are more expensive. http://www.driveswarehouse.com


I have seven VFD's powering my machine tools from my 20HP metalworking hydraulic planer to my smallest drill press. I'll never go back to single phase power for major shop equipment.

The de-rating question of VFD's for the home shop user may require more than a simple 50% answer. It's a matter of how much: The math works out to a three phase rated VFD running on single phase adequately serves a motor up to 2/3 it's rated capacity. If the VFD is designed for single phase power then you can use it to full load capacity.

More advanced consideration for de-rating VFD’s include questions like. How much single phase 120 Hz ripple in the DC buss can the VFD can handle without the logic or the power section being adversely affected under full load at @ 60 Hz? How much extra current and filter capacity is there in the rectifier section?

As the motor speed for a full torque load is reduced, the demand from the DC buss decreases accordingly until about 41 Hz is reached. At that point full load motor current can be theoretically be drawn from the VFD's load terminals. The rectifier and DC buss still thinks it's working into a de-rated load because of the output transistor's PWM duty cycle at the lower voltage/Hz.

So it's full reted current to the load terminals up to about 41 Hz and a linear decrease thereafter to about 70 percent of full load current. This will limit the VFD's input diodes to no more then the three phase full loat current. As for ripple current that's a fuction of the installed filter capacity and has to be figured (or scoped) for your particular VFD.

A three phase rated VFD destined to feed a 1.15 service factor motor run to full name plate ratings from single phase power needs to be DOUBLE rated, that is a 5 HP motor requires a 10 nominal HP drive. The de-rating protects the input diodes which may be rated for three phase amps.

Most manual machine tool drives seldom require full motor HP. A three phase rated VFD will be acceptable if 1 1/2 times over rated, that is a 5 HP motor will work well from a 7 1/2 HP drive. There will be a corner between about 45 hz @ full torque and 60 Hz @ 3/4 rated torque where the VFD limits motor performance. Most modern feature-rich drives allows the drive to be programmed at constant HP in this band of operation. There will be no harm to the motor or drive. The motor will merely act as if overloaded.

Most of these concerns are moot because few - very few - people in home shops take full HP cuts for more than a minute or so.

I just bought a 15 HP Allen Bradley 1336F VFD to run my lathe to a full 10 HP (the old stone age 7 1/2 - 10 HP Magnetek wasn't handling the lower RPM's very well even on low torque). I was thinking I'd do that piggy-back power supply trick on it.

There's never a simple answer to any question regarding AC.

By the way, connect nothing to the third line terminal of the VFD. No ground, not to the single phase line. Resist temptation and leave it unused and innocent ot wire. Someone mentioned connecting the neutral to something.

Connect the neutral to nothing but the return leg of any 115 circuits forming part of the electrical systen. Do NOT connect the branch circuit neutral to ground at any point in the electrical circuit except to the neutral/ground rail at the service entrance in compliance with local code and NEC. Connect the ground to the chassis of the VFD at the ground terminal provided.

Also be sure to continue the ground conductor through to the motor and other electrical loads following the VFD's installation book guidelines to avoid ground loops.

Concerning questions about running motors from VFD's at low RPMS

Often home shop machinists wish to take advantage of VFD technology for their single phase machine tools but a conversion from single phase to VFD control takes some thinking. For one thing a VFD will not run a single phase motor. Period. For another you cannot replace a step pulley or multi-speed geared spindle transmission and vary the spindle RPM’s with the VFD alone. Any attempt to do so results in frustration as the spindle speed is reduced at the VFD’s speed control knob. It’s a matter of mechanical advantage.

Some complain that “VFDs lose torque at low RPM’s.” That’s false. Torque is twisting effort. Power is a function of torque times RPM. An induction motor is a constant torque device. As you reduce the motor RPM with the VFD the motor's torque remains constant but the RPM's and consequently power drops proportionate to the VFD's setpoint frequency. A 1 HP motor designed to run at 60 Hz develops 1/2 HP at 30 Hz, 1/4 hp at 15 Hz, and so on. No motor torque is lost as the RPM's are reduced only the delivered power.

What is mistakenly called "torque loss" is actually loss of tangential force. When it's necessary to run larger cutters at lower RPM the torque requirement goes up. If you attempt to obtain lower RPM by dialing down the VFD bacause the moment at the cutting edges is larger you also reduce the available power at the cutter. If a full HP cut is desired the spindle speed has to be mechanically - not electronically -reduced to suit the cutter RPM.

For that reason you cannot dispense with a machine tool's multi-step mechanical reductions if you wish to take advantage of the motor's full HP. Use the VFD to fill in between the steps for max HP and for low power operations use the VFD. If you wish to be lazy and avoid shifting belts or gears it's OK to use the VFD alone but only for lighter cuts in proportion to motor RPM.

Thrift store or garage sale? Don't buy it if pre-1995. Get a return agreement and have a local motor guy check it out. These drives are nearly bullet proof but their NEMA 1 enclosures are built like a bird cage. If the internal electronics are permeated by conductive dust (like from an abrasive shop saw) the logic and switching circuits will suffer. Older VFD's are 6 step and squeal when they run and are bereft of important features. The newer PWM drives are quiet and more resistant to faults.

As for the economies of VFD Vs a phase converter, there are several. A spinning phase converter running idle draws idle current depending on about a dozen variables. Actual charges are strongly dependent on duty cycle and power factor. As long as the phase converter is running you pay for the KW/hrs the converter ticks up on the meter whether you are drawing power from it or not.

As for conversion efficiency, I'd guess that a machine tool drive motor run from a VFD consumes about 1/3 the power over a year that a comparable motor fed from an across the line starter.

All modern VFD’s have "economizer circuitry". If the motor is run at part load, the VFD drops the line voltage to some level where the motor runs at reduced voltage closer to full load amps and its greatest conversion efficiency. My lathe motor is 10 HP and is rated for 230 Volts 3 phase @ 34 Amps. When I'm coasting along taking a light cut, the motor draws about 23 Amps from the VFD at reduced voltage but the VFD draws only about 4 Amps from the line. No this is not smoke and mirrors but simply how real-world VFD's work with real world three phase motors.

Most industrial motors are over-rated in their application and therefore run inefficiently. About 1/4 of all electrical energy is consumed by motors 50 HP or less. We in the US wouldn’t have to build new power generating plants for years if every three phase motor was furnished with a VFD.

The subject of an older motor's behavior with VFD's includes many urban legend style stories based more on self-accreting hearsay than actual performance. Not to trivialize the point but motor heating and insulation failure are concerns frequently overstated by popular belief particularly on 230 Volt systems.

Every motor has a duty cycle rating which is the percentage of time it can be safely run to full ratings. Most induction motors have duty cycle ratings of 100% or more meaning there is no limitation to operation except ambient the air temperature can be no greater than the safe insulation class temperature rating minus the motor's rated temperature rise. Since motors have thermal mass it takes time for the motor's copper temperature to increase to dangerous levels even at overload current. Makes sense; otherwise a motor would burn out at start-up.

Most induction motors running power tools have a relatively low duty cycle, even during stock reduction roughing cuts. The time between cuts counts as idle time permitting the motor a breather when it can cool somewhat.

You can run only one motor at a time from a VFD and you really should run the motor from the control panel not switch the motor after the drive. You may desire to purchase one VFD and run several items of equipment from it by plugging them in separately as you need them. Just remember that you may wish to adjust parameters every time you change motor for the built-in motor protection features to work properly.

Inverter rated induction motors have extra insulation strength to resist transient over-voltages induced in the windings by the switching frequency. New motors have stator iron properties favoring high frequencies therefore high voltage transients and insulation breakdown can be more of a problem when run from VFD's. Older motors have older iron which incidentally better blots up high frequency switching transients so it causes less of a voltage spike problem than would seem. Thus older tech motors mitigate effects newer motors have to be designed for.

It's long been the rule that induction motor insulation (and any other electrical appliance or device for that matter) has to with stand double the connectable voltage plus 500 Volts. So long as the motor is dry, VFD switching transients will cause no trouble for the home shop machinist running hid equipment from 230 Volts..

Finally I include a photo section showing the conversion of a drill press to single phase input VFD drive with a tapping feature. This conversion while a little fancy is quite simple to accomplish on manual lathes and milling machines if there are electrical smarts handy, a willingness to tinker, and of course that most precious of home shop resources a talent for scrounging.
 
Matt,

I planned to shut off my main power breaker while doing any wiring like normal. My main power at the service breaker is: 115v / 115v / 208v.

Thanks guys.
 
TSims,
Sorry if I sounded discouraging, far from it, the electrical and electronics classes I took many years ago have been a big help in my career and if you're interested I highly recommend you do the same.

But the way you described your power supply (120+120+220=460 3ph) sounded way off and your motor would smoke in a hurry if hooked up that way.

You said you had 3 phase so it didn't make sense to me. Forrest correctly I'm sure recognized it as single phase and told you how to take it from there, along with a thorough lesson on motors.

Always listen to him and you'll be far ahead.

Regards,
John
 
Forest,

Thanks for you response. I just printed it and will read it on the way to the race track today.

This is at my business not residential power.

-Taylor Sims
 
No problem, thanks guys. Looking forward to learning another one of those mysteries in life
 
Now I see why it takes eons to get something shipped. Busy writing books. It was 24 June 07 when he elected to ship them back. Wonder if I have the right year?

:D

John
 
Forrest - I just saved your excellent post into a 21 page Word document. Thanks again for all you contribute to this group.

Steve.
 
Geez Forest

Looks like you really missed the forum when it was down and had a whole lot saved up you wanted to say. Excellent information BTW - as always

TSims

Go out to your Electrical panel box and write down the "Name Plate" information for us. Or better yet take a picture. That will settle any disputes as to what type of electrical service is available at your place of business
 
Joe,

Outside panels name plates are:

1st panel; 100 amp
240VAC-10 7.5HP Std 15HP MAX
240VAC-30 15HP Std 30HP MAX

2nd panel; 200 amp
240VAC-30 25HP Std 60HP MAX

3rd panel; No label but has meter
4th panel; Same, no label.


Voltage from leg to leg on all the panels inside are 240v. Sounds like I have single phase correct? I have to admit that I am dis-appointed. Was told there was 3 phase power in the building.
 
Forrest,

That's impressive! All you ever need to know about motors! One thing... you did hit on ODP used in non metal, vapor bearing environments. Expounding on that, I often rebuild semi hermetic commercial refrigeration compressors. Sometimes when a suction reed fails a piece will blow back into the motor area, the intense magnetic pull in the rotor gap will pull that piece in. That has always resulted in a major short. Thus I would highly discourage anyone tempted to install a freebie or cheap ODP motor in their machine shop. TEFC only.
 
TSims,
Don't rule out having 3 phase just yet, you say 240v between all legs, if it was single phase you probably would have said- between both legs.

Easiest visual way to tell besides looking to see if the breakers have 3 segments, is pull a cover off and count busses. These are where the incoming feed wires attach to a lug on each buss which all the breakers attach to. In US for 240v they're normally taped red, white, black. (sometimes not at all).

If you have 3 you're in like Flinn and don't need a VFD although Forrest pointed out their many advantages.

I'm sure you're eager to get the BP on line, I just didn't want to see you burn it up right out of the gate.

If you do have 240/3, wire it up like matt_i showed for low voltage and you're in business.

Good luck,
John
 
jmead,

You are correct I said all because I do in fact have three bus bars on almost all of my heavy power panels.
That does make me feel a little better!

Before I smoke my new purchase can I restate what I understand this to mean for clarification?

Matt_i wrote this:

For low voltage:

L1-1-7
L2-2-8
L3-3-9
4-5-6

Does this mean that a lead off Bus bar one is L1, the lead off bus bar two is L2 and, the third bus L3.

I am then to connect Lead1 (L1) with wires tagged 1 and 7. L2 with wires tagged 2 and 8. And L3 with wires tagged 3 and 9. Then wires tagged 4,5,6 are paired?

I sure appreciate the help and advise.
 








 
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