VFD/Welder question?

Anyone know if a VFD can safely (without blowing itself out) run a 3ph welder?
Ive a 25hp older VFD, which appears to be unused, and a 300 amp 3ph MIG
welder.
Is it possible to run the welder, from the VFD, from single phase power, without blowing out the VFD?
Id have to say it would smoke the VFD..but..Im not particularly knowlegeable about this aspect of VFDs.
Gunner
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Gunner Asch wrote:

In all of my travels, a VFD (Variable frequency Drive) is intended for driving a motor. Anything else and you are asking for trouble.
There are 'inverters' or 'converters' that can change DC (or single phase AC) to 3 phase AC. Unless your unit is spec'd for that use, I wouldn't spend too much time trying to get this to work.

Got a model number for that VFD?
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On Sun, 06 Jun 2010 17:55:16 -0700, "Paul Hovnanian P.E."

http://cgi.ebay.com/20-HP-TOSHIBA-TOSVERT-G2-AC-MOTOR-DRIVE-VFD-130G2-20HP-/130383048916?cmd=ViewItem&pt=BI_Control_Systems_PLCs&hash=item1e5b6f70d4
Its nearly identical to this one, but 25hp and 220 volt
Gunner
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Gunner Asch wrote:

http://cgi.ebay.com/20-HP-TOSHIBA-TOSVERT-G2-AC-MOTOR-DRIVE-VFD-130G2-20HP-/130383048916?cmd=ViewItem&pt=BI_Control_Systems_PLCs&hash=item1e5b6f70d4
If you could figure out how to turn the drive on when you want to strike an arc it would be better. If not, how about a three phase motor as a dummy load when the welder is idling?
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Not for sure but I think the VFD would kick out without damaging the drive if it didn't like the load. If you have some of the inductors that they put on the output side it seems it would help if the welder isn't seen as an inductive load.
A guy at work used a Hitachi 10HP drive to run a refrigeration pump system. The pump kicks in and out but they also have some circuitry to run. They were able to set the drive to 45Hz and when the pump kicks on it doesn't kick the drive out at 45Hz like it does at 60Hz. So the drive powers their control circuitry at 45Hz and when the pump kicks on the drive is ramped up to 60Hz and they said it works great. They are using a 10HP drive for something like a 5HP motor though.
RogerN
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wrote:

I'll preface this by stating that I am an EE with some experience in power electronics but have zero hands-on experience with VFD's.
First question is whether or not your 25hp VFD was designed to operate from single-phase power. It's certainly possible, but it would require a raft of energy storage caps. A VFD synthesizes 3-phase power from DC that it gets by rectifying its supply.
A VFD supplied from 3 phase power doesn't require many if any caps because rectified 3-phase voltage never goes below about 86% of peak. Rectified single phase supply goes thru zero twice per cycle unless there is capacitive storage to carry the load during those periods.
Beyond that, welders and induction motors are both inductive loads and I think a 25 hp VFD should have no problem supplying the draw from a 300 amp MIG welder. 300 amps at 28 volts is about 11 hp.
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Gunner Asch wrote:

I'd say the biggest risk involves the nature of VFD's where they don't like a switch between them & their load. Now, you could leave the welder switched on & use the VFD to power it up & down, but the question is: does the starting & stopping of the arc look like load switching to the VFD? I.e., it's a huge load change that might be the kind of problem for it that load switching is.
Me? I wouldn't risk the chance of ruining the drive. Maybe the factory can help?
Bob
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What's that Lassie? You say that Gunner Asch fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Sun, 06 Jun 2010 16:51:47 -0700:

Looks like you have made up your mind not to try it.
But if you had to try it:
Run a large 3ph motor in series with the welder. And put a flywheel on it. When the arc is struck, the motor should act as a generator to soften the load on the VFD.
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On Tue, 08 Jun 2010 04:11:50 GMT, snipped-for-privacy@privacy.net (dan) wrote:

Ayup..thats pretty much what Id come up with too. But not curious enough to actually try it if there is any danger of it smoking either the VFD or the MIG
Thanks!
Gunner
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(dan) wrote:

If you hook up the drive and motor sometime, I don't know if you have an oscilloscope with high enough voltage probes lying around, but you could look at the waveform at the motor.
It would probably work if you happened to have 3 large transformers, maybe primary 220/440, secondary 110/220, connected 220 IN, 220 OUT. The voltage going into the transformers should be pulse width modulated square waves but you should have something that resembles a SIN wave coming out of the transformers.
Maybe examine the welder schematic to see where the power IN goes to, and see how the 3 phases are used. My Miller 330AB(?) TIG runs off of single phase 220/440. I guess you have to consider the value of the welder as a welder versus as copper scrap though!
RogerN
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What's that Lassie? You say that dan fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Tue, 08 Jun 2010 04:11:50 GMT:

I meant parallel, not series.
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What's that, Dan? Lassie just pissed on your leg? Well, it WAS a male dog in the TV program.
Steve
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