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  1. #1
    Hi all, I may be preaching to the choir here but in case Im not here goes:
    Most stepper systems increase their high speed performance when you increase their PSU voltage.
    High voltage and current linear PSUs are pricey and heavy although nice to have.
    It is the case however that PC ATX or AT power supplies can be stacked in series!
    Semi modern PSUs have at least 15A on their 12V rail, modern ones, (10 new from websystems in Notts), have over 30A on their 12V!
    All you have to do is make sure that for all the PSUs bar one you have isolated the black ground output wires from the case & earth pin.
    This generally involves opening the PSU and insulating the board from the case with a bit of plastic. Use a multimeter on continuity mode to check if the case is still connected to the black wires on the output side.
    In the past I have done this to test power a large 24V to mains inverter and it worked fine!
    Switchmode PSUs need a minimum load to regulate properly so all I do is load the +5V rail with about 5ohms of high powered resisters inside the case and job done.
    These PSUs can be pulled out of old machines in skips etc if your skint or bought new if you're time poor and money rich.

    Full details here:
    and here

    Its quite possible to get above 60V at 30A with a stack of 5!
    Im about to make a 36V at ^15A supply for my new motors so I'll post photos here.
    If anyone needs advice etc then get in touch, in this thread would be best because then everyone benefits.
    All the best, Jim

  2. Jim,

    Funnily enough this was being discussed on another thread last night, I have done the same myself before. Thanks for the links, they are useful.

    I've not found you need as low as 5ohm (1 Amp load) on the 5v rail, thats 5W dissipation (10W rated resistor). I found 47ohm (0.1A, 1W rating) adequate.


  3. #3
    Yes, I know what you mean; I did find however that if you power 5V logic from the same supply you can get brownout type glitches because the 5V rail can bounce and sag if you connect and disconnect a large load on the 12V rail.
    I found that doesnt happen (as much) if the resister load is pulling a couple of amps.
    It may just be my dodgy skip salvage PSUs tho...

  4. #4
    Yep Irving, yesterday we were discussing a cheap 24v PSU for Diycnc's drivers and 2 ATX psu's are a great "power to buck" solution.

    Another cheap alternative would be a laptop PSU, There are loads of 20v 6 amp PSU's on ebay for around 13 which may be sufficient for your machine, I think they would be great for someone of a less electrical background aswell as no live terminals to stick fingers in!!!!

    Another advantage (though maybe not over ATX PSU's as they are well sheilded) is that we could avoid bringing that nasty mains noise into our control enclosures.

    Not sure if there is anything more powerful available in the laptop PSU area?


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