Old 230/440 motor and VFD

My Bridgeport is a lot more than 45 years old, and I've not had a problem running it's 220/440 motor on the VFD.

Given your proclivity for this sort of thing, you ought to be smart enough to just move. Yeah, it's a pain but so what? Make your life look like your end game, or desires.

Only you will be able to determine this by actually running your motor from a VFD

Gunner

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...It no longer has valid reasons to exist. Lorad474

Two things to consider:

1) Cooling at low RPMs. Not a big deal if all you are doing is producing 3 phase at or near lie frequency. 2) Effects of HF harmonics on windings and rotor. This is a bit trickier to guess about. Some motors need their rotors grounded (through a slip ring or something similar) to prevent HF coupling from the stator to the rotor from returning to ground through the bearings. That can erode them.

I do not need to change frequency on this lathe.

I just wanted to not have to run the phase converter.

Right now the lathe runs off of a phase-a-matic static converter box, but that is not too good for the motor, and does not give me the full HP.

This is kind of my issue right here.

i

Given your ability to find a deal, is there any reason you can't come up with a rpc? I'm running mine on a Rotophase my uncle found in a dumpster at a oil location he maintained portapotties at. A motor, a few caps, you are good go to.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

a rpc? I'm

I already have a phase converter, but I was hoping I would not need to use it for the lathe. I have a pile of variable frequency drives, some are in a bad cosmetic shape (hard to sell) that are quite usable.

i

a rpc? I'm

maintained

I don't know enough about VFD's in your application to help you.

It would seem that a motor that is 230/460 which I belive yours in could handle whatever extra strain a vfd would put on it.

I don't know but would adding some load side capacitance mellow out how your motor reacts? I'm hoping our EE's on the list have comments on that one.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

with a rpc? I'm

he maintained

motor reacts?

I am pretty sure that you cannot put capacitors on the output of a VFD.

Actually right now, the lathe is on a Phase-A-Matic static phase converter. The Phase-A-Matic came with the lathe. It runs, but I am getting only 2 HP out of 3. Maybe I should just leave it as is. I would not be likely to use all of the HP without coolant.

I want to do the right thing, and it is not immediately obvious what is the right thing. I know for sure that I do not need to vary input frequency.

It seems that the phase converter route is nicest to the motor, and lathe, but is less convenient for me.

i

Correct, VFD PWM output is designed for inductive load usually a V/F ratio based on the rpm your vfd is set at. Capacitors placed on the output will change the pulse width and could cause the motor to overheat at less than 60Hz settings. In addition you will be creating a LC circuit with its own set of problems that VFD's don't like. You might end up with a multi kilowatt AM transmitter of sorts.

Best Regards Tom.

with a rpc? I'm

he maintained

handle whatever

motor reacts?

There's now way of being sure but the odds are pretty good.

VFDs increase the peak voltage stresses on the motor insulation, Most older motors survive (all that I have used) but a few fail. Capacitors do NOT help.

The yard stick I would use is simply based on the mechanics of the motor installation. If it's difficult or impossible to replace it with a modern motor then it makes sense to stick with an RPC.

If on the other hand it's a fairly standard motor that could be replaced if disaster struck I would chose the VFD drive on the basis that the increased convenience outweighs the small increase in risk.

Jim

...

You could add an insulation tester (Megger) to your search list:

The hand-cranked ones are safer because they shut off if you get a zap and stop cranking, plus you can check old motors on the shelf without needing AC power.

If you find two real cheap, I could use one.

jsw

Great

Jim, do inductors help? Those line reactors, would a line reactor help if I installed one between the drive and the motor?

It is not very special. Here's a picture.

Looks like 184T to me, but could be an old frame size due to it having been made in 1966.

I also like Jim Wilkins' suggestion of trying to test insulation with a megger. This would be my first time of using a megger. I believe I have one from my old military surplus days.

i

Jim, I thought I had a megger, thisi s a GREAT idea and I will try it. I would say that if insulation can survive 800v, I should be fine.

i

But you can put inductance in series with the output to dampen the harmonics. Don't know the specifics concerning Iggy's VFD, but I've seen it done on pump station VFD's in a residential neighborhood.

Line reactors are useful because they slow the rise time of the transients but, unless you've long cable runs, the effect is not large. It's probably not worth buying a set but if you happen to have one on hand you might as well fit them.

A megger test is certainly helpful but even that doesn't give you full assurance. It's a very long time since I signed off equipment but the test yardstick in those days was twice peak working voltage plus 1000V.

Jim

motor reacts?

Sorry. It was late, my brain wasn't in gear. I have a severe head cold.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

I ran a Bridgeport M-head motor off a VFD. The crummy less-than first generation VFD eventually smoked when I tried plug reversing the motor. That motor worked SO MUCH better off a VFD than a static phase converter it was amazing. The motor was, I'm sure, the original 1938 motor on that mill.

Yes, the motor I mention above was a 230/460 V unit. I am also running a 1950's vintage J-head motor on a VFD now, and it also works fine. So, it also pretty much qualifies for your 45 year old question. I have run it for well over 10 years on a VFD with no problems. This is the Bridgeport "pancake" motor on 1 Hp step-pulley mills, single-speed 230/460 V.

Jon

motor reacts?

No, you do NOT want to put capacitors on the output side of a VFD. The VFD produces 400 V square waves of varying duty cycle, to create the right currents in the motor windings. Capacitors will draw huge currents on the edges of those square waves, and either fry themselves or the transistors in the VFD. You can cobble up an L-C filter if you really feel the need, but it shouldn't be nexessary in most cases. Old motors run in a moist environment might be more susceptible to insulation breakdown, so if you are running machines in an unheated garage, that might be more of a concern.

Jon