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Posted By: JohnnyB How to get this to work? - 09/13/03 11:41 PM
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.
Posted By: NJwirenut Re: How to get this to work? - 09/14/03 03:25 AM
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).]
Posted By: Bjarney Re: How to get this to work? - 09/14/03 04:51 AM
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.]
Posted By: Pinemarten Re: How to get this to work? - 09/14/03 07:06 AM
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.
Posted By: JohnnyB Re: How to get this to work? - 09/14/03 12:40 PM
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?
Posted By: russ m Re: How to get this to work? - 09/14/03 10:36 PM
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).]
Posted By: Big Jim Re: How to get this to work? - 09/15/03 01:51 AM
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
Posted By: Trainwire Re: How to get this to work? - 09/15/03 09:42 AM
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.

TW
Posted By: JCooper Re: How to get this to work? - 09/15/03 03:46 PM
Is this equipment still operating? Would it be possible to rewire the feed back at the panel to get your 120 at the disco?
Posted By: Bjarney Re: How to get this to work? - 09/15/03 09:30 PM
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).]
Posted By: frank Re: How to get this to work? - 09/16/03 12:15 AM
Bjarney,
I was just thinking the same thing.
Posted By: JohnnyB Re: How to get this to work? - 09/17/03 05:10 AM
For temp power, 277 to ground.
Posted By: JohnnyB Re: How to get this to work? - 09/17/03 05:19 AM
I looked into the welder, it uses a transformer and a reactor? I'm going to assume that the transformer cannot be rewired to higher voltage due to its a cheap welder. I'm getting the welder for real cheap so thats why I'm trying to make it work and I know I've got some jobs that I'll need it.

What about useing a heating element in series with the welder? Like a fin type element compact enough to make it worth the effort?
Posted By: NJwirenut Re: How to get this to work? - 09/17/03 08:32 PM
A resistive ballast MIGHT work if the current draw was constant, but a welder is definitely NOT a constant current load.

Transformer or genset look like the way to go here.
Posted By: electure Re: How to get this to work? - 09/20/03 11:06 AM
Have you tried this welder plugged into a normal 20A 120V circuit?
As Trainwire mentioned, the unit won't draw the maximum current unless the welding current is turned all the way up.
I used a Lincoln 225 "buzz box" for corral fence repairs for years. It was powered by only a 20A 240V circuit, sometimes with 300'+ of #10 and #12 extension cords. Although the welder had an input rating of 50A, I never had a bit of trouble.
I don't think the 277 to ground connection is a safe idea under any circumstances...S
Posted By: JohnnyB Re: How to get this to work? - 09/20/03 02:31 PM
I have used it in my garage and it blows the 15amp if I exceed the duty cycle. That’s easy since it’s only got a 20% so that’s 20% of 10 minute interval. If their is sufficient voltage drop the duty cycle gets shorter.

What are the potential hazards of the 277 to ground? The chassis and conduit could carry current. The ground could be wet and a shock hazard could exist. I think most likely the clamp will loose its connection and I will lose my full 277 and smoke my welder.
Posted By: Pinemarten Re: How to get this to work? - 09/23/03 11:16 AM
JohnnyB, you said in an earlier post that you 'assumed' you didn't have a higher voltage tap in your welder. If it is 'cheap', it may be designed for all countries and therefore have the taps you are looking for.
The 'resistance in series' may work, but you have to choose it for your optimum amperage.
Posted By: JohnnyB Re: How to get this to work? - 09/30/03 03:53 AM
It's a Sears mig welder, 70-80 amp. I think they are made by lincoln. I looked in the parts break down and it didnt show any extra taps. I thought the difference between us and everyone else was just 60HZ to 50HZ.

Hey Pinemarten, I too like to read about astrophisics. I just re-read "A brief history of time". Have you read "The elegant universe" or are you familiar with Brian Green at all?
Posted By: Pinemarten Re: How to get this to work? - 09/30/03 09:40 AM
The easiest way to check the taps is to take it apart. It may have an auto-transformer with no labels or labels that don't make sense.
Went you wire it to 120V you should be able to meter the voltage on the other taps. If another tap meters 208, 240, 277, or 480 etc then that is where you tie in to that voltage.
If you have a motor winding shop in your area they can take a quick metering of it and make sure you:
DON'T TAP INTO THE SECONDARY!
That would be a noisy, smelly, painful, and generally bad thing.

I don't read many books on astrophysics but I studied it in highschool. My best updates come from badastronomy.com
Posted By: iwire Re: How to get this to work? - 09/30/03 10:10 AM
I really feel the safest and only code / listing compliant way to use this welder on the roof is to find a source of 120 volt power that can handle this welder (20 amp 120 volt circuit) and run a cord from there.

The cost of a cord of large enough to deal with voltage drop may cost more then renting a gas powered generator.

A 5000 watt portable generator should easily power this welder.
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