Would like a computer power supply for other purposes without a
motherboard connected. Either AT or ATX? Has anyone done this? If so,
how?
Any help?

Sure,

Computer power supplies (types AT & ATX) both output 5 volts (yellow wire) &
12 volts (red wire), just don't exceed the wattage output which is probably
on the power supply label.

For instance, if the device you are powering needs 5 amps at 12 volts, your
power supply needs to be capable of at least 70 watts (dc voltage x dc
amperage = dc watts)

AT power supplies are the easiest since they are generally not reliant on
the motherboard and have a physical switch. ATX power supplies generally
have a purple wire that I think you have to tie to the yellow - could be all
wrong on that, it's been a couple years but that's the general idea.



"birdman" wrote in message
oups.com...
Would like a computer power supply for other purposes without a
motherboard connected. Either AT or ATX? Has anyone done this? If so,
how?
Any help?

Jerry Boone wrote:
Sure,

Computer power supplies (types AT & ATX) both output 5 volts (yellow wire) &
12 volts (red wire), just don't exceed the wattage output which is probably
on the power supply label.

It's a LOT more complicated than that.


For instance, if the device you are powering needs 5 amps at 12 volts, your
power supply needs to be capable of at least 70 watts (dc voltage x dc
amperage = dc watts)

5 X 12 = 60



AT power supplies are the easiest since they are generally not reliant on
the motherboard and have a physical switch. ATX power supplies generally
have a purple wire that I think you have to tie to the yellow - could be all
wrong on that,

Yes, you could

it's been a couple years but that's the general idea.







"birdman" wrote in message
oups.com...

Would like a computer power supply for other purposes without a
motherboard connected. Either AT or ATX? Has anyone done this? If so,
how?
Any help?

Bottom line is that computer supplies are UNSUITABLE for most
applications. Yes, you can think of a zillion places where it would
work. But if you have to ask the question, you're unlikely to be able
to tell where they're applicable.

If all you need is noisy 5V and don't mind welding your screwdriver
to your circuit when you slip, you're likely to be successful.
mike

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birdman wrote:
Would like a computer power supply for other purposes without a
motherboard connected. Either AT or ATX? Has anyone done this? If so,
how?
Any help?

I use an AT supply for a bench supply. I removed all of the PC cables
except one drive power lead. Then I mounted binding posts, a switch and
an LED on the front panel.

A few words of warning:
- Discharge the main filter cap before working on the board. It can
hold a charge and shock you
- Insulate well. AT supplies have a line voltage switch. Keep your
wires far away from line wires. Pick a switch rated for the right
voltage/current.
- The 5V and 12V lines can supply a large current. They can melt thin
wires. This is another reason to insulate well.
- Some supplies need a load on the 5V and maybe 12V output to work
properly. Use resistors or a tail-light bulb.
- There are a lot of cheap supplies out there that are poorly
engineered. Current limiters may not work well. I accidentally shorted
the -12V output of my first one and blew out every semiconductor from
the output to the line.
- 'Power Good' is an OUTPUT. It goes (TTL?) high when there is power.
Use it to drive an LED or leave it unconnected.
- Check the fan while you have it apart. On old supplies it probably
needs oiling or replacing.

You can see a picture at of the one I built at
http://shawnd.dyndns.org/photos/Power_Supply.jpg

That is exactly what I need , +5, +12, and -12, I was not aware that
an AT Ps would powerup without having a motherboard pluged to it. I
have an older peice of video equipment that does not have a power
supply. This would sure solve the problem.
Thanks

On Wed, 19 Jan 2005 21:19:11 GMT "Jerry Boone"
wrote in Message id: :

Computer power supplies (types AT & ATX) both output 5 volts (yellow wire) &
12 volts (red wire),

You've got your colors reversed.

birdman wrote:
That is exactly what I need , +5, +12, and -12, I was not aware that
an AT Ps would powerup without having a motherboard pluged to it. I
have an older peice of video equipment that does not have a power
supply. This would sure solve the problem.

It may not come on without a load. Mine does, but it depends on the
circuit design. Add some power resistors or a light bulb if it doesn't.

If it is for a specific device I would also suggest fuses on the supply
lines since I doubt you want 25A going into the 5V input of your device.

On 19 Jan 2005 12:33:33 -0800, "birdman" put
finger to keyboard and composed:

Would like a computer power supply for other purposes without a
motherboard connected. Either AT or ATX? Has anyone done this? If so,
how?
Any help?

To power up an ATX PSU without a motherboard, short the PS_ON* pin to
ground.

See http://www.hardwarebook.net/connecto.../atxpower.html

If you intend to use a PC PSU to provide split rails for op-amps, etc,
then be aware that the -12V supply is often not regulated.

With some minor modifications you could convert a PC PSU into a 13.8V
supply for radio and car audio gear. I have also converted an AT P/S
into a high current 6V supply. The mods entail reprogramming the
voltage sense resistors and uprating the overvoltage detection
zener(s).


- Franc Zabkar
--
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