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I know arc welders typically require 15-30 volts and 100-200 amperes to work.

I have two microwave transformers in which I have removed the secondary winding and wound 15 turns each of heavier wire through.

I am planning on connecting the transformers in the fashion shown in the image. I want to know if there are any glaring issues with my design.

  • Will there be enough current/voltage to strike an arc?
  • Are there any probable failure points in my design that I should look into?
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    \$\begingroup\$ You might want to add some current-limiting on the primary - once you strike the arc, it will be almost a short-circuit. \$\endgroup\$ Commented Sep 9, 2024 at 19:04

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The power you can get is limited by the fact that you're using a 125V / 15A feed. This limits you to no more than about 1200 watts (80% of 15A @ 125V.) That's about the power handling capability of the transformer too.

Compare that figure to 30V at 100A, or 15V at 200A: 3000W, well over what that socket can deliver.

Related: https://diy.stackexchange.com/questions/72733/what-is-the-maximum-load-for-each-of-the-standard-us-120v-electrical-outlets#72734

Then there’s the transformer. Even if you had a larger feed, the transformer couldn't take it since that sort of load is beyond its working range.

Typical transformer welders on the other hand use a 30A/240V feed. With over 6kW available that feed can easily handle the welder power demand.

In short, doing what you propose will pop your breaker frustratingly often, while not getting enough heat to your arc to get the job done.

Can you do this hack for spot welding? Sure. Induction heating? Yes. Arc welding? Nope.

Maybe useful: a short primer on welder power.

MORE: 125V welders do exist. These are rated at 140A or so. However, these are inverter types so are much more efficient than transformer welders.

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  • \$\begingroup\$ Wouldn't the trasformers in series be able to deliver twice the power? Granted, the issue with the socket remains. \$\endgroup\$ Commented Sep 9, 2024 at 19:31
  • \$\begingroup\$ Yes, they could. But at what point does it become worthwhile compared to buying a welder, which manages both its voltage and current for optimum results? \$\endgroup\$ Commented Sep 9, 2024 at 19:38
  • \$\begingroup\$ I think it is clear that the welder solution is the best one under several different metrics, but it is also important to keep in mind that perhaps OP does not have access to a welder for some reason. The reasoning about the socket is certainly correct, but I don't think OP mentions the 15 amp limit - perhaps something that is common in the US but not so much elsewhere. All in all, I think you provide a great answer, but there are some assumptions in there that might be wrong. \$\endgroup\$ Commented Sep 10, 2024 at 7:13
  • \$\begingroup\$ ‘110V’ outlets with a standard NEMA 5-15R socket are 125V 15A. This applies for all ‘120V’ countries. \$\endgroup\$ Commented Sep 10, 2024 at 18:50
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    \$\begingroup\$ That is true, but for all we know OP is in a situation where getting a welder is just not an option - we do get questions from areas of the world which are unlucky enough not to be reached by the usual online retailers, nor any big box store. Or perhaps OP just wants to experiment... \$\endgroup\$ Commented Sep 11, 2024 at 7:15

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