7v off an old psu is not working!

[JFettig]

i have a spare 250watt psu and i was modding my fanbus to have a switch from 12 to 7 volts, and every time i switch from 12 to 7 it just shuts off, or when i try to turn it on with it at 7v it just turns the fan like 5 degrees and stops.

but then i tried hooking the fan directly to 7v and it did the same thing.
and i remembered that i hooked a fan directly to 7v on my new 400watt psu and it worked so i tried it and well, it works on my new one but not on my old one that i like to test with....

anyone got ideas?

its like it shorts out and blows a fuse...

[Hoot]

The PSU is automatically shutting down to prevent damage to it from occurring. Almost everyone thinks being able to misuse the outputs of their PSU to be some kind of gift the PSU manufacturer failed to mention. Truth is, they don't mention that capability because the PSU was not designed to work that way. Mercifully, many PSUs are tolerant of being misused and people get away with doing that trick.

Assuming you are not using the +5V output for any other circuitry, chances are you need to place a nominal load on the +5V output. Pick up a 4 ohm (commonly found) 10W power resistor and place it between the +5V output and one of the return wires (black). That will probably allow you to also get away with misusing you PSU, like many others are doing.

Good Luck

Hoot