View Full Version : Three phase ?

larry mullen
03-22-2010, 01:01 PM
Can you use a vfd to run a 3 phase welder with single phase in a shop? what would be your options ?
Thanks larry

Ken Hosford
03-22-2010, 01:14 PM
My understanding is yes you can run 3 ph motors on single phase with vfd units . That is one of the awesome benefits. Though if running different speeds it is harder on motor windings , they make motors for vfd use specifically with higher temp insulation but if you are not crowding power output and running close to rated speed probably not an issue

Marty Comstock
03-22-2010, 01:46 PM
I have researched this a little bit, and I believe that you can convert a 3 phase welder to a single phase unit, but that it wont ge as efficent or "strong" as it used to be because youll have 2 transformers on one leg, and one on another, where in 3 phase it would be one transformer per leg. I could be mistaken here, need to find out more.

As for running off a VFD, I honestly do not know.


03-22-2010, 01:58 PM
Not something that would be wise to do. But, if you decide to try it let us know how long the VFD lasted.


03-22-2010, 02:27 PM
Larry, there are surplus 3 phase diesel generators out there, I think it maybe be overkill, but I bet you win the "my welder is bigger than yours" debate!

larry mullen
03-22-2010, 03:34 PM
appreciate the input . Sounds like it would not be a wise choice .
Thanks larry

03-22-2010, 04:36 PM
Can you use a vfd to run a 3 phase welder with single phase in a shop? what would be your options ?
Thanks larry
The short answer is no you cannot. A VFD is designed to run a motor, not a welder. The long answer follows. :p

I believe Marty is right. Especially if it's an inverter type welder. Then the primary is just the same as a VFD just without the secondary part that adapts it to a motor.

An inverter works by rectifying the AC input to a DC voltage. Then this DC is chopped up to make it an AC voltage in a VFD. Or to a high frequency in a welder. In the welder this high frequency is run through a transformer to make a lower voltage. The high frequency allows the use of a much smaller transformer than a 60Hz transformer. Thus a lighter and cheaper unit. This lower voltage is again chopped up to give the desired amperage and DC (or AC in some welders).

So by connecting your 2-phase directly to the welder instead of through a VFD you leave out several conversions and thus do not suffer as much in losses.

Edit: You have a TN grid and not IT as we have, so not 2-phase but 1-phase. But the above still applies.

03-22-2010, 06:13 PM
I've seen a three phase MIG welder powered by a home made rotary 3 phase converter. It made beautiful welds for a lot of years. The welder was an old Miller.

03-22-2010, 06:38 PM
Assuming we are talking about a transformer type welder it might work. In many ways a transformer and a motor are very similar in the way they react electrically. For that reason in my mind it may well work, but think of the size of VFD you would need. My large welder is fused for 100+ amps on each leg so you would need a very large VFD to supply that amount of current. Will it work I am not sure but I think so. Is it worth it I am pretty sure its not because of the cost of the large VFD. If you did try it I think it would be best to stay very close to the design frequency on the welder.

www.gogitzit.com (http://www.gogitzit.com)

Rod S.
03-22-2010, 08:30 PM
Larry I am a certified welder repair tech. Not recommended to run a vfd on a welder they were designed for motors. That being said you can run a three phase transformer type welder on a rotary phase converter but it requires a big horse converter and takes a lot of power to run. As was said above most inverter welders can be run single or three phase with not to much difference in output but the duty cycle suffers a little. But heck metal shapers usually dont need big three phase welders for what we do any way.

Rod S.