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Can anyone show/tell me how I can make a benchtop 12 volt power supply from an electric motor and a car alternator? Answered


To answer th' question as asked ,  You need a washing machine motor ,  a car battery and alternator and a set of pulleys to step up th' alternator to a little above 2000 rpm from th' motors 1750 rpm !

If you use a GM 1 wire alternater then that is about all you need !

Using the parts mentioned you can't make a 12 volt power supply.

And it is listed as taking about 2 hp to turn the alternator up to speed when drawing power from it.

Maybe you caint ,  but I did it when I wuz in th' US Navy and stationed in Scotland and needed a way to run my 120 volt universal motor dremel tool !

It did work ,  but in great part 'cause I was usin' a BIG diesel truck battery and a cigarette lighter type inverter !  Th' alt wuz a 100 amp modei off of a big Rover sedan ! 

Thinkin' about it ,  if you aint gonna run it in th' house you could use a 3 1/2 hp Briggs and Stratton lawnwower engine ( governed to run at 3500 rpm as built) and set th' alt in a vertical position with 1 to 1 pulleys !  You must run some kind of flywheel to compensate fer leavin' off th' blade or th' bugger wont run !

There are not the correct parts to make a bench top power supply in what you describe.

I guess you could salvage the wire from the motor and hand wind a stepdown transformer and use the diodes in the alternator to rectify the voltage.  But I doubt that it would be worth the trouble.

If you used the motor to turn the alternator you would still need a 12 v. battery to energize the alternator.  Alternators are not self energizing.

Better bet would be to sell the motor and alternator and buy a 12 v transformer and a bridge.  Radio Shack has a transformer for about $12 and a bridge for about $3.  Then scavenge a couple of capacitors and you've got a pretty good power supply.

Or find a dead computer and take the power supply out of that.  There are several instructables on this site to do just that.

I did the latter, you can pick up a used power supply for peanuts, got mine from a computer fair for £5, it's small for a computer but for my purposes it's more than I'll ever need. Plus the work involved in getting it running is minimal, and some will come with cool features like telling you when the supply is stable and providing a separate 5v low power supply even when main power hasn't yet stabilized.