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Tutorial Request: PC PSU to bench power supply
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Tutorial Request: PC PSU to bench power supply

by wesg on Mon Nov 22, 2010 1:37 am

Using an Arduino generally requires electricity at 9V, 5V and 3.3V and a PSU can supply 2 of those 3 voltages. I've seen a few pages online about turning this machines into bench top power supplies.

Could there be a tutorial -- or at least documentation -- about converting an old PSU into that kind of power supply? Personally I would find it very useful, as I want to build one of my own.
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Re: Tutorial Request: PC PSU to bench power supply

by adafruit on Mon Nov 22, 2010 1:38 am

they dont work very well due to the way they require loading, so we dont suggest them at all.

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Re: Tutorial Request: PC PSU to bench power supply

by richms on Mon Nov 22, 2010 4:25 am

wesg wrote:Using an Arduino generally requires electricity at 9V, 5V and 3.3V and a PSU can supply 2 of those 3 voltages. I've seen a few pages online about turning this machines into bench top power supplies.

Could there be a tutorial -- or at least documentation -- about converting an old PSU into that kind of power supply? Personally I would find it very useful, as I want to build one of my own.


Green to black on the ATX connector with a switch of some type, and then use the other wires for what you want to power.

Chuck some USB and car lighter sockets on it for good measure, and the load to make it run can be prettymuch anything. You dont need to load all rails on most of them, so a reasonable load of a couple of fans on the 12v is usually enough to make them settle down. Even the fans in the PSU should be enough to have it start and run, but the rails may be a bit unstable. An incandesent car lamp will be fine as a load.

PC PSUs dont like lots of capacitance on the output, I was using a couple to power a car amplifier, and they didnt like starting up with it connected, and they would shut down if just connected straight to it. In the end I put a 21watt brake light in series with the amplifier initially, then closed a switch across it once the light went out (2-3 seconds) and it was fine.

Once PC PSU's shut down, they dont power up again till AC is removed and the capacitors discharge in them. They also lack the current limiting that a proper bench powersupply offers which is good when testing things so you dont smoke up things that you wire up wrong.

If you want to do it non destructivly to the powersupply there are heaps of ATX extenders of 24 to 20 pin adapters you can get, plug into the PSU and then hack up the cables on the $2 extender.

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Re: Tutorial Request: PC PSU to bench power supply

by cybergibbons on Mon Nov 22, 2010 10:27 am

I can't see why people continue to use ATX power supplies for bench work. 3.3V at 30A? 12V at 25A? No protection except against direct shorts? Loads of noise? Refusal to power up with too low/high/funny loads? Bad handling of dynamic loads?

I'd either pay £10 for a wall-wart, £80 for a proper bench supply, or use something like the breadboard power supply.
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Re: Tutorial Request: PC PSU to bench power supply

by pstemari on Fri Dec 03, 2010 1:30 pm

To comply with the current ATX spec you need an 18 ohm 10 W resistor on the +12v and 22 ohm resistors on the +3.3v and +5v, 2W on the +5v, about 1W on the +3.3v. Large and clunky, and once you start looking at adding current sense resistors to get just current metering, let alone current limiting, the project starts looking much less attractive.
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Re: Tutorial Request: PC PSU to bench power supply

by westfw on Fri Dec 03, 2010 7:44 pm

Using an Arduino generally requires electricity at 9V, 5V and 3.3V

Why do you think that? One of those is usually enough. The original Arduino design has a regulator because it used a serial port (which doesn't provide power) and most wall warts of the day were unregulated, but in "modern times" I've been thinking that you could get by with JUST the usb port (power+comm or power only) (given the wide availability of 5V regulated power supplies, and the use of USB jacks as general purpose (~5V) power connector.

I've always wanted to turn an entire old computer into a test instrument.
Stick a power supply "front panel" into an external drive bay, use the sound card as a scope, manage most of your device programmers, etc. http://www.instructables.com/id/%5BIdea ... onics-Eng/
Why worry about properly loading a bare power supply when you already have a nice box that does that for you, and incidentally can do a bunch of other things as well...

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