run 3phase ac drive on 1phase?

Many times one runs across VFDs or AC drives that specify 3 phase input. Can you generally/sometimes run one of these on single phase, while expecting suitable derating? I believe it would be much like running a 3 phase motor on a static converter.

My Hitachi can take either 3 phase in or single phase in, and it states this explicitly. My question is if you have a VFD that does not mention single phase, is this possible?

found a thread...

I think I found my answer here:

http://www.practicalmachinist.com/vb/showthread.php?t=153478

You usually can.

Some VFDs have to be de-rated by 50% to run on single phase. Most 3hp and under VFDs can run on single phase without derating at all, but they kinda hide that information in the manual. Bigger VFDs over 3hp are usually meant for 3 phase only. Some can be run on single phase, you have to set it to ignore the fact there's a missing phase, because they have a protection feature to shut them off when 1 phase is out. There MAY be some VFDs that won't run on single phase AT ALL!

All VFDs work the same way, they take the incomming AC current, and convert it to filtered DC. When they run on single phase, the incomming current goes through 4 diodes (two for each hot wire), and the filter capacitor has to be bigger to compensate for the missing phase. On 3 phase, there are 6 diodes sharing the load, and less time between phases, so they can use a smaller capacitor. The more horsepower the VFD can support, the bigger the diodes and capacitor(s). The rule of thumb is you need a VFD that can support double the horsepower of your motor if it's to be run on single phase.

The majority of VFDs are designed for three-phase input (fixed frequency) and three-phase output (variable frequency).

Some VFDs in the 3 HP and under ratings are specifically built for single-/three-phase input with no derating for single-phase input. These do not require a larger frame size.

Other VFDs in the 5 HP and under ratings are specifically built for single-/three-phase input with no derating for single-phase input. These do require a larger frame size, usually a 7.5 HP frame size to accommodate the larger converter section. But these VFDs are limited to 5 HP for the inverter section.

A new line of VFDs is specifically designed for single-phase input in all sizes. Three-phase input is not supported at all.

looking at a 20hp vfd for a 7.5hp motor

It is a Yaskawa GDP506/P5. It is rated for 20HP, 27amps@460V. Seems like I should be able to run a 7.5hp table saw with this, no?

Also a ABB ACG501 rated for 7.5 HP, 440-500V input. This one sounds like a candidate for feeding it DC from an external bridge rect and filter cap.

I want to run a large older bandsaw with a 5 HP motor capable of handling a 1" blade in the usual home softwoods and some hardwoods. The original was a large ol' crotch 3 ph of about 1.5 hp or somesuch and had a flat disc commutator if I recall. I am told it was intended for relatively non-stop running and was probably from the 20's -30's.

I have a 240v line going into my shed and could run the saw as single ph 240.

Assuming a 5 hp motor, is there a point in going specifically to 240 1 or 3 ph?

I also have a piece of hydraulic equipment in the shed which is already set for a 3 ph. I can have a 3 ph line from from the pole in the alley. Therefore the issue is running both pieces as 3 ph with one or more phase converters on a 240 line.

I could go with one to three converters and cover a third compressor which is 3 ph. But should I just have a line run from the alley and have it all wired? Total available current with the fewest pieces of supplementary equipment is one issue. Ability to have max current and amps available is another consideration. What is the best path to follow?

I have had an electrical company over twice but the issue of converters apparently threw them for a loop. I have been waiting weeks to hear from them.

One of the things to keep in mind with running a lathe on any RPC or VFD is having to reverse rapidly while threading. Thankfully the lathe is usually not turning at high RPMs tho.

This situation comes up when cutting metric threads with an english leadscrew or english threads with a metric leadscrew. For this operation you can not disengage the half nut or you will have to pick up the thread again which is not real difficult but it ain't easy either.

RPCs and VFDs will draw huge amounts of current for a significant time period during this operation.

Hydraulic pumps will place extreme loads on an electric drive motor when reversing also.

For this reason an RPC for a lathe needs to be 2X the lathe HP at a minimum. I don't even want to think about derating a VFD for those applications.

Even tho there is 3Ø available on the pole it is usually high voltage and will need 3Ø transformers. You will be paying commercial electric rates and for the transformers etc, -read mega $$$$$. If someone else is already using 3Ø and the transformers with enough capacity are already there then it is only moderately expensive, but you will still be paying high commercial electric rates.

Once the electric company has been informed that you are running high power equipment they might just come out and determine you have a bad power factor and throw some big rate increases at you.

Torque1st said:

One of the things to keep in mind with running a lathe on any RPC or VFD is having to reverse rapidly while threading.
RPCs and VFDs will draw huge amounts of current for a significant time period during this operation.

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Not any VFD that I have ever run does. It brakes, comes to a stop and takes off again all speed controlled. Properly set up, a VFD will have no surge when starting or stopping the motor.

Here is one graph of a 3 phase motor starting, running at 60 hz and then stopping.

Sorry but for reversing a lathe during a threading operation the ramps have to be extremely fast, much faster than those shown or the thread relief must be overly large. -Otherwise CRASH!!!

Torque1st said:

Sorry but for reversing a lathe during a threading operation the ramps have to be extremely fast, much faster than those shown or the thread relief must be overly large. -Otherwise CRASH!!!

Click to expand...

The current drawn by the VFD cannot exceed it's peak current rating else it will throw a overcurrent fault. As far as instant reverse goes, the VFD falls short of a RPC or grid power. The VFD will almost always have a longer stop time due to the current limits built into the drive. When equipped with a resistor the the VFD can sink more current but peak current still isn't as high as throwing reverse under grid or RPC power.

Like I said, I wouldn't even try to figure out how to derate or even setup a VFD to handle that type of "emergency" reverse.

Torque1st said:

Like I said, I wouldn't even try to figure out how to derate or even setup a VFD to handle that type of "emergency" reverse.

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You don't have to derate anything. The VFD is self limiting. If you tried a full power reverse by changing wiring you break the cardinal rule about VFDs and in addition it would just fault out and you would get no braking whatsoever.

I use a v/hz VFD on my lathe to cut threads and it is a joy to cut metric threads. The variable speed pot is the key to happiness.

I have my braking set to either .2 or .3 seconds. While not instant stop, it works well. I could have gone lower but was afraid that constant braking like that could be detrimental to the life of the gears. A more robust lathe should handle braking like that just fine.

Pierce Butler said:

You don't have to derate anything. The VFD is self limiting. If you tried a full power reverse by changing wiring you break the cardinal rule about VFDs and in addition it would just fault out and you would get no braking whatsoever.

I use a v/hz VFD on my lathe to cut threads and it is a joy to cut metric threads. The variable speed pot is the key to happiness.

I have my braking set to either .2 or .3 seconds. While not instant stop, it works well. I could have gone lower but was afraid that constant braking like that could be detrimental to the life of the gears. A more robust lathe should handle braking like that just fine.

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I am well aware that you can't reverse the motor leads with a VFD.

I probably cut threads a little faster than some people do having done it in a production shop, usually between 100-150RPM depending on the lathe. A .2 or .3 sec reverse might work.

the VFD's are 440v input

Well, I got the 2 VFD's described above. Alas, they are both models designed for 440v in and out.

The Yaskawa GDP506/P5 actually does indicate that you can feed it single phase on terminals L1 and L2, and derate it 50%. As was mentioned here, that little crucial bit is buried in the manual.

However, my reading of the manual says that I need 440v in. I think I may try giving it 220 on those 2 legs and see what happens tho. I don't imagine it would hurt.

manual here:
http://www.yaskawa.com/site/dmdrive.nsf/link2/MNEN-5JLRL2/$file/TM4029.pdf

Now the other unit - an ABB model ACH501-007-4-00P2-MB says that it is rated at 440v in as well. But the output is "VIN"- so maybe this means that the output is the same voltage that you put in, and that can be up to 440 (actually 500).

manual here:
https://www.abb-drives.com/StdDrives/RestrictedPages/Marketing/Documentation/Documents/ACH501-04.pdf

So- if feeding these things 220vac doesn't work, I reckon I'll be looking for step-up transformers.

If a VFD doesn't have nameplate or installation manual ratings for single phase service you have to treat it as a three phase rated unit. If you want to run it from single phase you have to crank in some fudge factors so your VFD to be happy with the motor it serves.

I have several three phase only rated VFD's I run from single phase power. You gotta remember that most machine tools are low duty cycle not like a pump or blower where the load is constant. A minute or so of full HP heavy roughing then a minute of cranking back and dialing in with maybe a size check equals 50% duty cycle. the other 90% of the time it's in service the machine loafs along taking lighter cuts and fine finishes. The motor demand will be correspondily lower and the demand from the line will be lower yet depending on the Hz setpoint. If the motor is run at 40 Hz or below (varies with motor service factor and VFD max current ratings) you don't need to de-rate a three phase rated VFD at all.

If you wish to run a motor from a three phase rated VFD to full ratings from single phase power you have to work the math. Start with the full load motor amps @ 3 Phase Vs the VFD ratings. The input diodes of the VFD are rated for the nameplate load rating. The filter capacitors are sized for the three phase bridge ripple current. The VFD's output transistors are rated for the VFD's three phase full load. All this is complicated by environmental factors, demand , duty cycle etc so a flat statement of X de-rating may not hold up to technical scrutiny.

The best we can do is generalize on some rules of thumb. Here's mine:Generally, a VFD serving a motor expected to be loaded to 60% FLA can equal the motor HP. A VFD feeding a motor loaded to about 80% needs to be rated at 2/3 the motor HP. A heavy duty motor running a 100% duty cycle for extended periods of time needs to be double the HP rating of the motor is serves. Students of the topic can quibble these figures but I believe them to be reliable enough for first estimates. IOW YMMV.

A 20 HP VD may be overkill for a 7 1/2 HP motor. Its current detecting circuitry may not function properly at too small an operating current. You'd almost have to try it and see.

As for accel surges, if you insist on dynamite accels a VFD will do them at a much smaller line current surge than across the line starts. For one thing the VFD will go into current limit if the accel is set too short. For another a VFD will "motor" the armature at best torque slip to setpoint RPM quicker and more efficiently. Compare that to an across-the-line start where the motor's magnetic field windnills accellerating the armature far less efficiently.

Much depends on the connected inertia. I have my lathe VFD set for 3.5 seconds accel and decel and seldom exceed full load line current even when accellerating the spindle to 2000 RPM with my biggest 3 jaw on it.

I have a 10 HP VFD feeding a 10 HP motor. I set the motor current limit to 35 Amps to save the input diodes from embarassment. The VFD is rated for 150% overload for some seconds (can't remember how many) so my dialed-in limits are safe for the rectifier stage and maybe the filters. There's been no smoke, smells, or loud noises for 5 years now. (knocking on wood)

plans for the VFDs

Thanks for the reply, Forrest.

My plans for the units are this:
The ABB 7.5hp VFD will go to a heavy duty A/B switch and run either a 5hp motor on a big table saw, or a 3hp motor (looks bigger) on a 16" jointer.

The 20hp Yaksawa VFD will run my 6x18 surface grinder and my universal grinder (od/id/face). I was thinking of using the VFD somewhat like a RPC- bring it up to a standard output voltage/freq, and then use the mag starters of these machines. Both of these units have 3 motors each and are currently wired for 440. It was suggested that if I am planning to use a VFD in this fashion, I could add an idler motor into the mix so that the VFD always sees an inductive load. Then use the normal starting circuitry for each machine. I might be better off to just complete my RPC instead of risking damaging the VFD by switching motors on and off, although an idler should help that.

The big issue is whether I need to come up with 440 vac to feed these VFDs, as they are both rated as such. It is hard to tell from the manual whether they REQUIRE 440 or whther they are CAPABLE of 440.

I dunno Iron. What you are describing is a perfect setting for a phase converter. A honkin' big VFD may not be a good choice.

VFD's are designed to run a single motor only. They do not make a good multi-motor phase converter even though it seems like they should. Every VFD manual I've read (dozens) says to connect the VFD output directly to the motor leads. There may be a work around; I don't know. My experience suggests the practical lower limit for motor HP for a VFD is about 1/3 the VFD's HP rating and the upper about double. That's just to run the motor. Getting usable power out of the motor has to be dealt with individually and generally involves juggling parameter setting to best advantage. Generally the best solution if you need to feed juice to several motors one at a time is - as you say - have an AB switch but the conductors have to go directly to the individual motors. No starters or control devices etc between VFD and motor leads - and you can run only one motor at a time from the VFD.

Thing is a VFD has a built in computer compares a long list of parameters to an algorithm describing three phase motor performance, then sends switching info to the output transisters while reading the motor current and sensing the motor's back EMF and integrating this with the rest. It's pretty high class stuff that doesn't work well with multiple motors, intervening motor starters, and other shake and bake home shop expedients.

The gadget you're looking for is a "Phase Perfect" solid state phase converter. It uses solid state electronics to make an electronic phase converter that does the job far more efficiently and in phase balance: it adds the third leg to the two single phase line conductors to make three phase juice. You then connect GP three phase equipment to it and run it just as though it was connected to a three phase utility.

A VFD won't do what a Phase Perfect solid state phase converter does. A VFD is intended to serve a single motor and run it at varying RPM's to suit the needs of the load. It has economizer circuitry the lowers the voltage to suit part load conditions etc.

ironhoarder said:

It is a Yaskawa GDP506/P5. It is rated for 20HP, 27amps@460V. Seems like I should be able to run a 7.5hp table saw with this, no?

Also a ABB ACG501 rated for 7.5 HP, 440-500V input. This one sounds like a candidate for feeding it DC from an external bridge rect and filter cap.

Click to expand...

Yes on the Yaskawa, it takes 1 phase input without issue.

No idea on the ABB, that number is unfamiliar to me. If you meant ACS501, it would probably be OK with, as you say, an external cap bank (assuming you know what you are doing with that). But don't rely upon the VFD's caps at all. ABB stopped selling those 10 years ago, so those caps are likely beyond their service life already.