Need a bit of fan wiring advice, If I want to run.....

[ErikS]

my fan at either 12v OR 7v then I need to wire my DPDT switch as follows: FanSwitch

Is this correct?

TIA

 

[squirrel dog]

I think you have it right.That should be slow,off and high.I am going to use pots,or a single pot.That would go from off to wfo,just like a volume control knob.

 

[ErikS]

Thanks, that's what I thought. I also thought it would be better to check before I ended up say "what's that smell?"

 

[fast_eddie]

ErikS;
the way that you labeled the switch; if you use +12volt and -5v you will be providing 17 volts to the fan when you are really intending to provide only 7v !!!!
if you are looking for 7volts, connect +5v instead

 

[ErikS]

fast_eddie -

Thanks, I just knew I was going to have a "sniff, sniff, what is that smell ?. I guess I forgot my math +12 + (-5) is 17, DOH!

 

[rectifire]

Yes.....never never connect anything to the -5V wire on the ATX connector.

The actual ATX connector wire(s) are the only place where you can get -5V from. -5V is meant to be supplied at very very low power (usually only a fraction of an amp), and should not be connected to any fans or anything like that. Even though you might be able to get +17V out of it (+12V) - (-5V)= 17VDC, your power supply would die quickly.

However, like the nice gentleman said above, you can get +7V out of the standard Molex 4 wire power connector. By connecting the fan between the +5 (red wire) and +12 (yellow wire), you will get a voltage differential of 7 Volts.

 

[Jhhnn]

Eric S-

You only need a spdt switch. hook the +12V directly to the fan, and switch the fan ground wire between system ground and +5V. If you want to use led's, ask fast eddie for his diagram, it's the best. There's a lot of bunk out there on this subject....

 

[ErikS]

Thanks, the more I think about it the more likely I'll got that way. For some reason I had it in my mind that I wanted to have an off position & there's really no need for fans.