View Full Version : 12v + -12v ---> 2x172mm's @ 24v
dobbz
04-15-2004, 11:08 PM
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 (actually 22v). the fans are rated for 12-28v 18W.
everything seems to be running fine. is there anything i need to look out for before the PSU blows up or something?
-12v line is very low amp line and that;s why you are getting 22volts imo.
Psu is lowering voltage to give needed amps.
I never heard about such a way of getting 24 volt line out of ATX PSU....
YOu need more imput here
dobbz
04-16-2004, 10:55 AM
well these are the fans: http://www.papst.de/pdf_dat_e/S32gb.pdf
ill probably end up running these at 12v actually. theyre just too loud at full speed.
Holst
04-16-2004, 11:03 AM
I wouldnt recomend doing this.
The -12v rail will have a low amperage (2amps) you may well blow up your PSU doing this... and if your PSU blows it may kill other stuff when it does..
NST6563
04-16-2004, 04:32 PM
If the positive is connected to +12v, then wouldn't the fan draw the current from the positive lead????
correct my thinking if it's wrong please. :)
enzoR
04-17-2004, 05:02 AM
no.....it may draw from it... "but it travels" though the -12v back. . . the -12 v is made inside the psu theirfore their is a limit of how much current can pass though it.
NST6563
04-17-2004, 02:47 PM
Originally posted by enzoR
no.....it may draw from it... "but it travels" though the -12v back. . . the -12 v is made inside the psu theirfore their is a limit of how much current can pass though it.
ahh..ok. I understand now.
guess he could try this link...I had 2 24v fans running off one of these from a dedicated power supply (ripped from a busted external drive enclosure).
http://murray.newcastle.edu.au/users/students/1999/c9221792/doubler.htm
dobbz
04-17-2004, 11:32 PM
whoa. that stuff is way over my head.
Ragnarok
04-18-2004, 01:39 AM
umm if u wanna use a voltage doubler for the sort of power output u need, then u gonna need some large :banana: :banana: :banana: :banana:ing caps..
as for the +12 and -12V, learn KVL and it will all become clear :)
dobbz
04-18-2004, 04:27 AM
Originally posted by Holst
I wouldnt recomend doing this.
The -12v rail will have a low amperage (2amps) you may well blow up your PSU doing this... and if your PSU blows it may kill other stuff when it does..
OK. its been running 24/7 for three days, still full speed at 22v and nothing is hot. i was hoping someone could gimme a headsup about when i should expect it to blow. cant say for sure?
like i said, the label reads 12v-28v, so is there no harm in running em with 12v?
Holst
04-18-2004, 05:05 AM
You can run them on the 12v line perfectly safely, its just putting them on -12 that may cause problems.
If you do want to run them on -12 then put a ammeter in the line and see what amps they are drawing.. if this is more than whats printed on your PSU then I wouldnt run them on -12.
Its impossible for me to say, if or when your PSU will be damaged, but I wouldnt run my own system like that.