I was just looking at some Youtube vids of a DIY spot welder, and thought the same technique could be used to make an analogue DIY 12V (or higher) PSU very cheaply. It uses a transformer from a discarded microwave oven, which commonly have their primary and secondary windings separated. In the oven it is a step-up transformer (and very lethal) to supply the magnetron with a few thousand volts, but by hacking off the secondary winding completely (whilst leaving the primary intact), you can wind a few turns of thick wire in the gap created by the missing secondary to make a high current low voltage transformer capable of delivering 800Watts or so (Look at [www.youtube.com] to see what I mean). That's more than 60 amps at 12V! By the looks of things you'll get about 1 volt per turn, so you only need to wind about 10 turns of thick insulated copper wire (thick automotive wire should work fine) - you can easily experiment to get the desired output voltage. You might as well choose the thickest wire that will physically fit into the gap to get the lowest voltage drop (and least heat). Then you'll need a full wave bridge rectifier capable of handling the current and a smoothing capacitor, though I shouldn't think it needs to be all that smooth as the regulator will iron out the low spots for the electronics, and I don't think the stepper motors are that fussy (BICBW), so a 1000uF 25V capacitor would probably be adequate (that's a guess). The rectifier in the microwave oven is not suitable, as it will be a high voltage but relatively low current device. You won't be drawing anything like the rated power from the transformer, so it should run reasonably cool. You could probably print the parts necessary to make a reasonable enclosure to mount the PSU components and a switched mains inlet socket (or switch & cable) perhaps also salvaged from the microwave oven, but keep an eye on its operating temperature to make sure nothing gets hot enough to soften the plastic, make the walls thick so it won't break and expose mains wiring if knocked - and position ventilation slots so that metal objects (and fingers) cannot fall onto or touch any exposed wiring.
Obviously anything connected to the mains can be dangerous, so I would not advise anyone to try it unless they have reasonable experience with electrical work and understand how to make a safe design.
Dave
(#106)
Obviously anything connected to the mains can be dangerous, so I would not advise anyone to try it unless they have reasonable experience with electrical work and understand how to make a safe design.
Dave
(#106)
