4th axis as a "poor man's lathe"

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Nice job you've made of that!

Thank you.

BTW, if you connect PSUs in series, it's good idea to fit a reverse polarity protection diode across the output (not in series), to avoid damage if you accidentally short circuit the combined output. Otherwise there is a good chance you can damage one (or more) of them by forcing it into reverse voltage.

It's a good idea. I will consider this, or some other solution, but I believe actually that these server PSUs have internal protection against all kinds of errors. These come from servers with dual PSUs connected in parallel, where if one PSU breaks down for any reason, the other will continue powering the server without interruption. So I trust these have all the protection needed, but of course, one or two or three extra safety feature is not a bad idea. That's why I have the overheat shutdown function also, even if I expect the PSUs will shut down on their own also. In fact, I know they will, since where we have used these at my work, there have been several PSU failures and not a single fire or any other damage. The servers been replaced by more modern ones, so I removed a few PSUs and reuse those before scrapping the servers.

Also the wiring to the shunt looks a little thin for 50A, although I'm guessing you won't be using the full current for a while.

The wires are 2.5mm² so it will be a while before those become a problem, but I will keep an eye on them when the current more permanently exceeds 15-20A. I think up to that I am definitely safe with those, and to be honest, I don't think I will ever use it above 20A, which is 1kW on the 50V side.