Power supply switches off

Hi
I have a small problem. I am using a printrboard interface and NEMA17 steppers and am currnelty just manually stepping the motors to check functionality. Every so often the power supply (A Dell PC power supply using the 4 way yellow and black cable connector) powers off and the only way to restart is to disconnect the green cable from the 0V.

I am guessing this is one of two things:

(1) I am drawing too much power for this particualr power supply or
(2) the steppers are drawing too much power and need turning down (I have already had a tweak of these).

Any pointers appreciated

Jonathan

Do you have a load on the 5V line of the PSU?
It is common for ATX power supplies to require a load on the 5V line to produce consistent power on the 12V line.

Thanks. I was told that connecting the pin 4 to ground would switch the supply on. Which it does.

I have been having a play this morning and it seems a bit erratic when it switches off and I cant seem to relate it to any specific cause, other than it seems to do it after I hit a button on the pronterface software to manually move an axis.

Still unsure of the cause.

Right, connecting pin4 to ground will turn it one, but many ATX power supplies have a feature that requires a significant load on the 5V line, without they load they either produce much less than 12V on the 12V line, or in some cases just turn off as soon as anything tries to draw significant current from the 12V line.
You can try attaching on old CDROM drive, it's usually enough, or put a 5-10 Ohm resistor on the 5V line, it will get very hot.

I concur with the loading the 5V. I've played with a few different PC power supplies and some of them required as much as 10W of draw on the 5V line to keep them from shutting themselves off. My associate Nathan had issues similar to yours in that he could never figure out what was tripping out the power supply, even with a good load on the 5V it would shut down on occasion.