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I ran across the diagram below in the mindtomachine blog post describing an homebrew arc welder. It shows two transformers with inputs in parallel and outputs in series. Is there some advantage to this arrangement rather than a single transformer with a doubled turns ratio?

Perhaps it's just what he had at hand, but I wanted to confirm with someone having EE background.

Welder Circuit

P.S. I'm not planning on building this, just curious.

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  • $\begingroup$ Would this be a case where they had used two old high current output transformers with the outputs in series to double the voltage ie just using what was available (second-hand) instead of buying new? $\endgroup$ – Solar Mike Jun 8 '17 at 20:40
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I would suggest that this is a case where they had used two old high current output transformers with the outputs in series to double the voltage ie just using what was available (second-hand) instead of buying new, a good example of re-purposing.

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Doubling the turns ratio is not exactly the same.

Yes, you get double the output voltage but you get different Magnetizing Inductance.

Moreover, the real reason to do something like that could probably be related to heat dissipation. The more wire layers you put, the hotter the center of the core will be for a given power. You could run thicker wire to offset this, but then you run out of core to wind. This could be specifically true for an arc welder in which voltage is actually reduced and you run very very high currents on the output.

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  • $\begingroup$ For sure, thermal effects might differ. But I don't think the guy who designed this particular circuit had much thought about that, in the video he said his power cord was melting. $\endgroup$ – Burt_Harris Jun 10 '17 at 1:21

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