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#29312 - 09/13/03 07:41 PM How to get this to work?  
JohnnyB  Offline
Joined: Feb 2002
Posts: 33
Chicago IL USA
I'm looking for alternative solution to this problem. I've got this little mig welder that uses 120v and I need to get it on a roof top for small welding jobs on HVAC equipment. My problem is the thing pulls 20+ amps and most of the power on the equipment disconnects is 480 3phase 277 to ground. I'm looking for an alternative to a transformer.

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#29313 - 09/13/03 11:25 PM Re: How to get this to work?  
NJwirenut  Offline
Joined: Sep 2001
Posts: 806
Bergen County, NJ
Does the welder have internal jumpers to allow you to run on higher line voltages?

A 120V receptacle is supposed to be provided near rooftop HVAC gear, for maintenance purposes.

[This message has been edited by NJwirenut (edited 09-13-2003).]

#29314 - 09/14/03 12:51 AM Re: How to get this to work?  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Unless you can try it well before hand, I would not count on a portable generator working, even if you could get it hoisted to roof level.

You may be able to find a surplus industrial-equipment dealer that would rent a 3-5kVA 240VX480-120/240V dry-type transformer, to set up in a 480-120V configuration. With this, you wiil also need a [surplus?] 30A 600V fusible disconnect switch to connect to the primary of the transformer.

Good luck on your project. A long extension cord from a 120V outlet may prove disappointing from a voltage-drop standpoint. [The transformer may weigh as much as or more than the welder, but may be the only way out.]

#29315 - 09/14/03 03:06 AM Re: How to get this to work?  
Pinemarten  Offline
Joined: Aug 2003
Posts: 123
Edmonton, AB, Canada
Just a thought but....
If you feel you have to go to a transformer, and your unit doesn't have the jumpers to go to 480; you may consider changing the internal transformer to one that does have the taps.
You could keep the old one as a spare.

#29316 - 09/14/03 08:40 AM Re: How to get this to work?  
JohnnyB  Offline
Joined: Feb 2002
Posts: 33
Chicago IL USA
unfortunatly, they are supposed to provide the outlets but don't a lot of the time. Those transformers are heavy and thats what I was hoping to avoid. HHHMMMMMmmmmmmm....

I will look into the welder being changeable to high voltage, but probably not as to its a cheap Sears mig welder. What about reducing voltage 277 down with ballast or resistance?

#29317 - 09/14/03 06:36 PM Re: How to get this to work?  
russ m  Offline
Joined: Feb 2003
Posts: 169
I have used some of these small welders, but they were 120v with 20amp cord caps. You might want to invest in a heavy duty cord even if you have to make it your self. If it draws more than 20 amps it must have a 30 or 50 amp cord and cap on it. We allways used heavy duty cords to reduce voltage drop.

[This message has been edited by russ m (edited 09-14-2003).]

#29318 - 09/14/03 09:51 PM Re: How to get this to work?  
Big Jim  Offline
Joined: Jul 2003
Posts: 394
Denver, CO USA
If you look at Lincoln, they have some pretty small 240 volt units that might run O K on 277. Better than trying to haul a welder and a transformer

#29319 - 09/15/03 05:42 AM Re: How to get this to work?  
Trainwire  Offline
Joined: Mar 2002
Posts: 360
Got one of those myself, complete with the gas. Amazing how handy they are once you have one.

If you don't run the thing turned up all the way you are not drawing the rated current. The ratings are usually for the welder turned all the way up. Running at half power might let you get away with making yourself the mother of all extension cords, eg, 10awg SO with some ends.


#29320 - 09/15/03 11:46 AM Re: How to get this to work?  
JCooper  Offline
Joined: Dec 2002
Posts: 228
Kendall Park, NJ USA
Is this equipment still operating? Would it be possible to rewire the feed back at the panel to get your 120 at the disco?

#29321 - 09/15/03 05:30 PM Re: How to get this to work?  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Offhand, I wouldn't count on finding 277V on a rooftop. Outdoor commercial/institutional unit-packaged HVAC gear doesn’t usually require a neutral, and it may even be missing in feeders to roof- or upper-floor-located panelboards solely for powering mechanical equipment.

[This message has been edited by Bjarney (edited 09-15-2003).]

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