Transformer for arc welding

Twentyfive Amps is insufficient for welding. You need from about 50 amps to

200 amps or so depending on the heat requirements for the gauge you are welding.

Six or eight ga. wire on the secondary? That's not consistent with 25 amps which would only require 10 ga.

If the transformer is designed to drive silicon carbide elements, it should have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something doesn't add up. We need actual specs to answer your question.

I think the OP was saying that 25A "continuous" works well. But I think the OP also wrote that this was an "industrial furnace for melting test specimens," which may have supported discontinuous currents that were higher. At least, I can tentatively accept the idea.

If the peak current it supports is more than 25A, the transformer rating might be higher. I don't know, so it's good to ask.

But here's a 10kW transformer that weighs 130 lbs:

To provide some kind of very rough weight vs watt benchmark.

Jon

to

amps

Agreed, but how much of a current overload is reasonable, 4 times? for 100 Amps out or something similar? Secondly where does the power come from? 120 VAC input is already over taxed. I can't imagine that one would expect to get 80 Amps out of a 120 Volt wall socket on a 20 Amp breaker. In other words this transformer sounds like a missmatch for welding. Too much voltage, not enough current.

should

add

10 kW, 130lbs sounds about right. Then shouldn't this 2500 Watt unit be about 33lbs?

Did the OP say it was a 2500 watt unit? I may have missed it.

Jon

amps

are

25 100 120

doesn't

He said 25 Amps and up to 100 Volts. Admittedly it's an arm waving kind of a discussion that why I asked for name plate specs. But, 120 VAC input is a dead giveaway that we are not talking about much power. Most single phase small kilns and furnaces run on 240VAC on 50 or 70 Amp circuits.

BTW, for welding it would be better if the current and voltage were reversed; i.e., 100 Amps @ 25 Volts.

The way I read the OP was that this was a repurposed unit, now being used as a kiln -- but not designed at the outset as one. Maybe I am the one who misunderstood, though.

Yes, I think you made that point abundantly clear. I have no experience and no reason to doubt it, either.

Jon

What are the duty cycles?

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Greed is the root of all eBay.

I bet you can use your transformer, at least for the job you're talking about. I've used a variety of transformers for welding, and many were not at all ideal..

What Might Work:

- Use small (say 1/16 or 5/64 ) CONTACT type rods only (Type 7014 I think) . You can start/keep an arc much easier than with other types. They work OK at 50 amps.

- You need approximately constant current, with a higher arc-starting voltage. So, use as much secondary as has both large wire and puts out

40 to 80 volts no load.

- Control the arc current with 'stuff' in series with the primary. I have used toaster elements, and those Edison screw base heating elements used in old 'reflector' space heaters. Back before I HEARD of binary I somehow figured out to use 3 switches with sets of toaster elements: 1, 2, 4 elements gave me, Hey! Anything from 1 to 7! I was a lot smarter in 1956 than I am now :-) This was on a bigger rewound pole transformer, you probably only need something like the resistance of a 1000 or 2000 watt 120V heater (total elements).

The voltage under load will be 25 or 30 volts, I think.

If this is REALLY a one-shot deal, use your jumper cables as welding cables.

REALLY, REALLY use a REAL welding helmet! Don't ask me why I know...

And, tell us how it went, so someone else can find your info!

Regards, Terry King ..On the Red Sea at KAUST snipped-for-privacy@terryking.us

Thanks, Terry. Yep, I definitely plan to use a REAL welding helmet, cables, clamp, and gloves. I was hoping to use some simple series inductance instead of resistance, but I do have some space heaters around that could do in a pinch.

For the other respondents who wondered about transformer kVA and current: The nameplate on the transformer only has volts and cycles (it's from the '40s or 50s), but the exterior furnace nameplate says that the input at 2500 degrees F is

1.55 kVA.

I may have been off on the weight, but my point is that cheapie stick welders have dinky transformers by comparison. They run them at *much* more current than what a conventional transformer would be rated at for continuous use, because they always have a "duty cycle" listed, typically in the 15% range. So you would be able to weld only

1.5 minutes out of every 10.

I'm sure I could get a much higher duty cycle out of this beast, but I have no need for that. My main concern is to not keep popping breakers.

Best regards,

Bob Masta DAQARTA v5.00 Data AcQuisition And Real-Time Analysis

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For reference: Typical welding duty cycle is about 30% for most shop work.. Time between welds to move things, reclamp, get another welding rod, etc.

Production welding like building a ship may be up to 80%.

My Lincoln Welder ($250 Home Depot class) is rated only (about 20% or so: not here) duty cycle at full output (225 Amps). But I rarely use that high a current for more than a minute or two..

That's why I asked. You can add some forced air cooling and even bolt large, finned heat sinks to the core to keep the transformer cooler as long as you aren't pulling moisture or corrosive material through the welder's cabinet.

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Greed is the root of all eBay.