Switching on a AT Psu

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16-01-2005, 09:13 PM
oshta

Switching on a AT Psu

How do you get a old AT PSU to switch on without a mobo?

- i though it would just be ON when you switched on the power, but its not?

anyone know how you get then to work?

daniel
16-01-2005, 09:17 PM
nvening

y do you want to?
16-01-2005, 09:20 PM
oshta

because i have a few kicking around, and i need a 12v power supply for the point motors on my model railway.
16-01-2005, 09:38 PM
BlueMagician

Quote:

Originally Posted by oshta

How do you get a old AT PSU to switch on without a mobo?

Yeah, I too was pretty sure that a generic AT PSU just had a push on/latch/push off switch. I'm sure I've just dragged one out in a shop before, and slapped in on the counter to power up a CD-drive I was thinking of buying..

I don't think AT's relied on having anything connected, ie: feedback from mobo or signalled ready. Might be wrong.

S.
16-01-2005, 09:40 PM
Daymonkey

cant you do the sort a green and black wire(i think) with a paper clip on this aswell.
16-01-2005, 09:51 PM
oshta

Well, i did a bit of digging, and aprantly most AT psu's need a light load on the 5v line?

according to this page http://home.cogeco.ca/~rpaisley4/ATpsu.html

daniel

[Daymonkey, thats for ATX psu's]
16-01-2005, 09:52 PM
BlueMagician

Quote:

Originally Posted by Daymonkey

cant you do the sort a green and black wire(i think) with a paper clip on this aswell.

I think the green+black bridge trick is just for ATX.. Again, might be wrong, sorry I can't be of more help.

S.
16-01-2005, 10:14 PM
oshta

Well, after reading that page, i did some playing.

0.8amps, and 5volts would need a 6.25ohm resistor (V=I*R)
- and a little shuffle and found a 6.2ohm in my box!! so i tryed it, and it worked!! - but it did get very HOT, so i tryed a 15ohm, which also worked, and only draws 0.33amp, so it cooler! (also tryed a 33ohm, but that wasnt enough)
16-01-2005, 10:19 PM
oshta

Ok, ive just been testing the 12v line, i got the set of bulbs i use for discharging my RC car battery packs, and conected them up (they draw about 6amps, which is nice, becuase the PSU is rated at 8amps)
- they work fine, but as i disconected it, the PSU triped, presumable becuase if over volted, becuase its not quick enought, so i conected the 33ohm resistor accross the 12v, and the now its fine at both conecting and disconecing and running a 6amp load

- and the two resistors stay just about cool enough if i leave them in the air flow of the fan, although i might stick them to a ram sink with thermal epoxy.

Thanks guys, daniel