12v + -12v --> 24v

[dobbz]

i have two Papst 6224/4 24v 172mm case fans running on a separate PSU's mobo connector. the positive lead is going to the 12v line, and the ground is going to the -12v line for 24v. the fans are rated for 12-24v @ 18W.

everything seems to be running fine. is there anything i need to look out for before the PSU blows up or something?

 

[jagec]

just don't overload it, and you'll be fine. If the fans are the ONLY thing you've got on that PSU, don't worry about it at all.

 

[dobbz]

well since this works, i wondered why PSU's dont have 24v connectors. is there any component on a board that combines 12 and -12 this way?

 

[kronchev]

Originally posted by dobbz
well since this works, i wondered why PSU's dont have 24v connectors. is there any component on a board that combines 12 and -12 this way?

nope

as for that load on the -12v are you SURE it can take it?? seems kind of high...

 

[BlindedByScience]

Originally posted by kronchev
as for that load on the -12v are you SURE it can take it?? seems kind of high...

P = V * I or I = (P / V); (18 * 2) / 24 = 1.5A which means that if the +12 and -12 are of the same magnitude, you're pulling about 750 mA off each rail. I'm pretty sure that +12 isn't an issue, but I'd sure look at the capability of the -12 rail. Most I've seen are there for compatibility reasons, and won't source much current. It definately depends on your specific PSU.

Regards - B.B.S.

 

[CallMeIshmael]

I would worry about the long-term effects on your PSU. Drawing that much current off the -12VDC line isn't good. The negative voltage lines from a PSU are intended for very low current logic circuits, not fan spinning. Most people who get the 24V papst fans for a PC are looking to run them at 12V for a quiet low-to-medium speed fan.

 

[dobbz]

yeah, thats why i got em. but theyre so incredibly fast and powerful at 24v i said fuggit. ill probably get tired of the noise and run em at 12v