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Joining Computer power supplies

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chiba

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I'm trying to come up with a cheap (read unregulated) 24V power supply that could handle around 12A. It's for powering a 24V dc motor attached to a speed controller. I know it would probably best be done with a Toroid, bridge and some caps but i remember seeing a page that hacked pc power supplies together. I know they can be joined in parallel without two many dramas but what happens if two switchmode pc power supples are joined in series? If anyone can help with what needs to be done or if they have a page that shows how then i'd be greatly appreciative.
 
You simply have to disconnect the secondary of one of the PSU's from chassis, otherwise it shorts the other PSU out.

How big are these motors?, is 12A the running current? - you need to bear in mind the massive starting current and stall current.
 
just don't let the chassis touch each other, then you don't have to modify their wiring. for best results, the power supplies should be as identical as possible.

as Nigel's pointed out, your motors may have much greater current demands at startup and if they stall. does your controller support soft-start of the motors? having a massive current draw hit those switchers will probably trip some internal safety regulator and shut it down.

oh, don't forget to give each switcher a minimum load on each of the rails - typically 1-2 amps.
 
Running switch modes in series like that is bound to be a pretty noisy business, but if it's just driving a motor..
 
Thanks guys, I tested it to 15A @ 24V, not bad considering these were rescued from the scrapheap. The motor is rated at 12A max, it won't see anywhere near that when running, but i wanted to make sure they could reach it.
 
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