Confirming my VFD conclusions

I've been lurking a long time but getting a Bridgeport at home made me register. Feel free to call my out on any stupid questions or forum etiquette issues. I just added a 1993 EZ Trak with as of yet unknown head issues, but the price made it worth it. This is going in my garage, so getting 240V single phase won't be an issue, but I don't have 3 phase.

1) Places I've worked that don't have 3 phase used home-made RPC's, but they were all put in place decades ago. It seems like VFD's are now the way to go, but I still see some people here using phase converters. Is this due to some benefit that only applies to shops running many machines, ie something that as a hobbyist I'm not doing?

2) VFC's are new to me, fortunately there have been lots of threads here to read about them. It seems like the one big feature is sensor less vector control. Is there anything else I should be looking out for?

3) The motor (original) is labelled as 2 hp, although there are some remarks in the manual about 3 hp intermittent use. Do I need a 3 hp VFD, or will a 2 hp VFD do? Is that a better question for the Bridgeport forum?

4) Most of the threads about which drive to select ended with a Teco (FM50/100 in old threads, N3 in new threads) or Hitachi WJ200. What I'm not getting an idea of is any notable differences (other than no vector on the FM50).

5) I'm not seeing much difference between the Teco N3 and L510. Am I missing anything obvious?

I'll be travelling for Thanksgiving, so I might be a bit slow about replying until Saturday.

Sensorless vector control is a feature of some VFDs, not of RPCs.

awander said:

Sensorless vector control is a feature of some VFDs, not of RPCs.

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Typo, thank you for catching that. I've corrected it.

To me it all comes down to how deep your pockets are..

If you ever plan on adding another 3 phase machine or even a machine with more than one motor, RPC is the way to go if you want to save money. For 215.00 you can buy a quality control panel with a simple push to start button. Add in a 10 HP used three phase motor, 150.00 in my case, and you're good to go. Takes about the same amount of time to wire up as a VFD and the next new machine just has to be plugged in.

I have a VFD on my Bridgeport boss spindle only because I want to tie the motor into the computer control system. It was running just fine with the original speed control and 3 phase power.

If you plan on having this as your only machine and it has one motor, VFD is a good way to go also.

Alternatively, you run the entire workshop from a single VFD that is capable of doing this. The PhasePerfect boxes are sold for this purpose. The Danfoss VFD I use is specced for the duty also,

A VFD has the advantage of variable speed. This is not absolute, because if you count on that for low speeds, you will have a lack of power, where belts and gears maintain power at low speed by increasing torque. Also, if you have multiple motors in a machine, you will need to maintain 50 or 60 Hz, because otherwise they will all change speed together.

VFDs also have limited current capability, and will not start a motor directly with a switch on the machine (unless over-sized by quite a bit), you have to start at zero speed and accelerate. The motor must be less than perhaps 1/4 of the VFD power before you can have a chance of starting it with a switch. So on a multiple motor machine, you would need to have a VFD significantly larger than the sum of the motor powers. You would then start the main motor with the usual slower acceleration, and then start whatever others are needed.

The RPC provides essentially the same sort of 3 phase that you would get from the power company, the difference being that power is more limited than power company 3 phase, since the RPC size limits the amount of load power you can get. You get no variable speed, but it will run any number of motors up to the power limit. Starting motors is normally not a problem, but the RPC needs to use an "idler motor" of at least 1 1/2 x the largest load motor.

So, a large RPC can run a whole shop with one device, but offers no advantages over regular 3 phase (other than the fact you now HAVE 3 phase). To use VFDs, you would normally have one VFD per machine (or more). So the RPC approach can be less expensive overall, if you do not need variable speed. Even if you DO need variable speed, you may not need it everywhere, so an RPC plus one or two VFDs for special machines is a practical approach as well.

Normally you use a VFD that is rated at the same, or sightly more, power than the load motor. An RPC would be rated at about the sum of the loads, and no smaller than 1 1/2 x the largest individual load, for best performance. So, if you had a 3 HP machine, and a 2 HP machine, a 5 HP RPC would power both and satisfy the 1 1/2x requirement. The RPC would happily start and run small (1/3 or 1/2 HP) feed motors and pump motors along with the 3 HP. If the smaller motors were much bigger than that, you need to consider their power, and might want to move up to a 7.5 HP RPC, depending.

To use VFDs, you would need both a 3 HP and a 2 HP VFD. If the 3 HP machine had a couple of 1/2 HP motors, you would likely need to make that 3 HP VFD a 7.5 HP instead, just to cover the current surges. (A 5HP might work, depending)

It is possible to run the whole shop from one VFD, yes, but it needs to be a big one, to cover motor current surges, since you won't want to shut off the whole place and bring it up slowly every time you want to start another machine. The Phase perfect units are made oversized so that they just plain work almost exactly like power company 3 phase. The Phase Perfect is slightly better than an RPC (or the power company, for that matter) as far as maintaining voltage and 3 phase balance, but generally costs a lot more than an RPC of equal capability. The Phase Perfect has NO frequency variability whatsoever, it just makes the 3rd phase equal to what's on the other two wires.

You bring up a good point about other motors. I was thinking VFD on the spindle motor, 1p on the controls. I didn't consider the x and y feed/control motors, I'll have to see if those are 1 or 3 phase. I plan to use it as a manual mill, but no sense losing the 2 axis CNC capability.

Someday in the distant future I could see a small lathe, but that's the only other 3 phase device I consider likely at this time.

Allen bradley units are rated for single phase and for 2 hp get 3 hp unit.

Ebay is good source at about 200 bucks or so.

I faced the same problem when buying my two speed, (3+2 hp) 3phase lathe. I went with a 10 HP American Rotary RPC rather than a VFD - mostly because the RPC can power any other machine I might want to buy in the future - which I actually am doing now, having gotten interested in a 3P OD grinder, which is being delivered this week. For the money I figure an RPC is much more versatile than a single VFD.

I bet you will want to upgrade or buy more equipment once you get deeper into machining. Buying tooling and equipment can become a never ending quest-- happily. An RPC opens the door to all kinds of industrial quality equipment you may absolutely decide you can't live without in the future ! Plus 3 p equipment often is cheaper, because 3P is not widely available except in industry settings.

VFD for a BP is a no brainer..

A BP sized VFD will not bankrupt you, and a RPC for other dumb machines (bench grinders etc) makes perfect sense.

Variable speed with the VFD, and easy on taps/head when direct power tapping.

Yes a RPC will run whole shop. It will not do a thing about that chatter, that could be eliminated by reducing spindle speed using VFD 24.5 rpm... Or the speed range gaps on gearhead or step pulley machines. Or let you run spindle (machine allowing) at 2x or more normal speed, when doing aluminum/plastic/wood work..

Using a big VFD to run different sized motors, provides no motor overload protection to the smaller motors.... Not for me or code.....

So get VFD's for the small lighter machines, Use a RPC for big equipment.

If you have a small 3 ph coolant pump on mill.. Replace it with a single phase one..

VFD control wiring is only ~12v at ~20 milliamps. Switches last forever. Since a VFD gives a soft start, splines and gears are happier...

VFD provides full motor protection to a single motor, and most provide ~120% boost for starting motor. A BP is not a hard start application...

For a BP get VFD rated same as motor .. 2 HP mill, get 2 hp VFD. I would dump the varidrive and go to step pulley.. No 100.00 special drive belt, no 1/3 hp lost as heat, from 1930's Reeves drive. No plastic bushings wearing and rattling. No motor spline getting chewed away.. No cranking on speed change dial, only while spindle is running.. VFD just twist knob 3/4 of a turn, min/max/running/stopped, it does not care..

I run a 1.5 hp motor on my step pulley. It stays in 2nd belt groove 90% of the time. Backgears and VFD handle most work there..

Thank you all for the replies so far

Glenn Brooks said:

For the money I figure an RPC is much more versatile than a single VFD.

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I'm coming to that conclusion, at least as running as single machine is concerned.

Glenn Brooks said:

I bet you will want to upgrade or buy more equipment once you get deeper into machining.

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I'll bet everyone says this, but I don't think I'm going to end up with a garage full of machines. I've been making use of the usual machines (mill, lathe, surface and rotary grinders, welder, band saw) for personal projects at places I've worked for the last decade. I frequently wish I had a mill at home, I occasionally wish I had a benchtop lathe, and maybe once every other year a welder, I never really wish I had the others and I still have access at work as needed. The real motivation other than this thing falling into my hands is that work is now an hour away instead of 5 minutes.

abarnsley said:

VFD for a BP is a no brainer..
A BP sized VFD will not bankrupt you, and a RPC for other dumb machines (bench grinders etc) makes perfect sense.
Variable speed with the VFD, and easy on taps/head when direct power tapping.
Yes a RPC will run whole shop. It will not do a thing about that chatter, that could be eliminated by reducing spindle speed using VFD 24.5 rpm... Or the speed range gaps on gearhead or step pulley machines. Or let you run spindle (machine allowing) at 2x or more normal speed, when doing aluminum/plastic/wood work..

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Double as in 8400 rpm? I could see that being handy for wood on occasion, but I didn't realize the machine could safely turn that rpm.

abarnsley said:

Using a big VFD to run different sized motors, provides no motor overload protection to the smaller motors.... Not for me or code.....
So get VFD's for the small lighter machines, Use a RPC for big equipment.

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Assuming the other motors aren't 3p (looks like they might actually be DC if I read the plates right) put a VFD on the mill, worry about a RPC if I end up with something that uses it later (different bench grinder, etc).

abarnsley said:

If you have a small 3 ph coolant pump on mill.. Replace it with a single phase one..

VFD control wiring is only ~12v at ~20 milliamps. Switches last forever. Since a VFD gives a soft start, splines and gears are happier...

VFD provides full motor protection to a single motor, and most provide ~120% boost for starting motor. A BP is not a hard start application...

For a BP get VFD rated same as motor .. 2 HP mill, get 2 hp VFD. I would dump the varidrive and go to step pulley.. No 100.00 special drive belt, no 1/3 hp lost as heat, from 1930's Reeves drive. No plastic bushings wearing and rattling. No motor spline getting chewed away.. No cranking on speed change dial, only while spindle is running.. VFD just twist knob 3/4 of a turn, min/max/running/stopped, it does not care..

Click to expand...

I can see the benefits of using a step pulley with a VFD (K.I.S.S.), but if this head turns out to be easy to fix I'm not sure it's worth buying a new head and selling this one? I doubt I'm going to wear this guy out in the time I own it.

This does make me wonder if it's worth putting a VFD on the light drill press at work. The VFD would cost about as much as the drill press, but I feel like I have to change the belt speed every time I use it.

abarnsley said:

I run a 1.5 hp motor on my step pulley. It stays in 2nd belt groove 90% of the time. Backgears and VFD handle most work there..

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"This does make me wonder if it's worth putting a VFD on the light drill press at work."

This is possibly the single best use for a VFD. I put one on my small drill press at work
years ago and would replace it instantly if it ever failed.

Liked it so much I put one in my similar drill press at home.

The VFD's star application, is for running a spindle motor. Sure, it'll run conveyors, pumps, and HVAC blowers, but where it really, really, really shines, is on a machine tool spindle.

When I first started my shop's collection of 3-phase tools, I built an RPC. Now, every one of my tools is powered by single phase, feeding a VFD. My Bridgeport J-head is set on the middle sheave combination, because at that position, there's maximum belt wrap on BOTH sides. Everything else I need to do, from running a 1/8" milling bit to a 4" boring bar, is done by selecting direct or backgear, and twisting the speed pot. I have EVERY machine set up for dynamic braking, so that spindles stop smoothly, and quickly. All the machines (mill, drills, lathes, grinders) are set up to run the motor to substantial overspeed (highest is around 215hz or so, for around 6,000rpm on a 1800rpm motor, and every motor has it's integral fan yanked and replaced with a quiet constant-speed 120v fan for continuous cooling at all rotor speeds.

My RPC is still standing by, in one of my other shops, for the sole purpose of being an easy-wire-up testing platform for machines that get brought in for testing.

With exception of one KBVF-24D and one Omron drive, all my machines are powered by Allen-Bradley 1305, 1336F, and 1336S VFDs, and I never paid more than $100 for ANY of them... most less than $50 as used take-offs. Some are 230v drives, but the rest are 400-480v, fed by dry transformers wired 'backwards', where AC mains feed the secondary connected for 240v, and primary wired for 480 is connected to two of the three VFD's input leads. I size the VFD a little larger than the motor when doing this, simply because the VFD's input rectifier is carrying all the power through just two of the three connections... so erring on the side of conservative ratings. Zero failures... ever.

Now that I've read up on this more I've come up with more questions than answers:
1) I've seen remarks about cheaper units claiming sensorless vector, but not doing a good job of implementing. This seems to be centered around older Teco units and off brand imports, so I think I'm safe here.
2) Some units require a separate braking module in order to use a braking resistor, but the cost for that module is high. It seems better to get something that already includes it.
3) I'm still stick on the 2 hp or 3 hp question. I have attached a picture of the motor nameplate below. The Hitachi WJ200-015SF also makes a similar 2 hp/3 hp reference on page 4 of the manual here:
http://www.hitachi-america.us/supportingdocs/forbus/inverters/Support/SM-E265_WJ200.pdf
Is that an appropriate unit?
4) It looks like the Teco units do not support braking resistors on the 230V/1p inputs. The L510 only has it on the 460v/3p model and if I'm reading the documentation right the N3 removed that capability in my HP range with firmware version 1.3.
5) I'm a little unclear of the WJ200 requires a braking module to use a braking resistor as the manual mentions both. I'll call them on Monday unless someone here knows for sure.
6) I'm having a hard time wandering around Allen Bradley's page. They seem to charge a solid premium for their drives. Are they including something I would need to buy separately from someone else, are they just more robust in the hazards of a production environment, or am I missing something else?

Motor plate picture:

One more thing:
It's been a while since I've done any 3 phase calculations, but 230 V at 6.2 A in 3 phase I get as right around 3 hp. The 230 V, 3 hp units though are rated for 11 A, and the 230 V, 2 hp units for 8 A. What am I doing wrong?

Order a 13xx series Allen bradley 3 hp and be done.

1300 new but 200 on ebay.

3 hp unit rated for 2 hp single phase input.

We have 2 and they are stupid simple to setup and can use existing switches to control logic imputs.

Tony Quiring said:

Order a 13xx series Allen bradley 3 hp and be done.

1300 new but 200 on ebay.

3 hp unit rated for 2 hp single phase input.

We have 2 and they are stupid simple to setup and can use existing switches to control logic imputs.

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The 1305 seems a reasonable fit, but does not mention sensorless vector in the operating manual, although I did find some references to "open loop". The 1336 does mention it directly, so perhaps that is the right model?

The ones I've found on ebay seem to be circa 1999, what is the lifespan on these? There were several threads mentioning capacitors going bad in them over time, although it seemed to involve mostly cold weather (which mine will see for a couple months of the year).

We have a 3 hp one on the 2 hp south bend and a 1 hp one that came on the BP with a 1 hp motor and it does okay but it was the variable speed head that went bad so po machine shoo swapped motor and varidrive with Toshiba motor and fixed pulleys and it needs back gear for slow torque.

No need for vector control or other terms...The BP came that way and when we picked up the SB it was suggested to do same and it was simple to install and the existing switch was used for logic input and a pot added for speed.

A meter was added using existing output set to show speed.

Toggle switch is a rated for 20 amp DP ST switch which is main power then know is speed and meter shows relative speed of motor.

Had it so what the heck...It can be set to show loading or frequency via a programmable output used to slave unit b from unit a.

These are older units but price was right and they are not offshore mystery stuff.