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Volts????????

They "need" 16V or they're "rated" at 16V? Would it be possible to give em some juice from a normal power connector, effectively "underclocking" them?
 
They are rated at 16 volts. I currently run them at 12 volts . But i would like to give them 16 volts for better air flow.
 
You don't. Computer power supplies put out 5V and 12V on all the auxiliary connectors. No way to get 16. Why not get fans that run at a faster RPM for the same voltage? They do exist. Of course, the tradeoff there is more noise. Whatever turns your crank! 🙂
 
Originally posted by: morkinva
Couldn't he run 1 x 12-v and 1 x 5-v connector in series
Click to expand...

That could work, not sure about the cap. though since it would be DC power going into the cap.
 
Originally posted by: motoamd
Originally posted by: morkinva
Couldn't he run 1 x 12-v and 1 x 5-v connector in series
Click to expand...

That could work, not sure about the cap. though since it would be DC power going into the cap.
Click to expand...

Really not getting the series thing......🙂 If you use the 12V rail and the -5V rail (as + and - ) or the 5V rail and the -12V rail (as + and - ), you can end up with 17V of potential (to lower that easily to ~16V you could put two diodes and the fan in series to get a drop of 1.4V so your not volting that fan over spec.

 
Here's what I mean.

edit>> You might want to try this with some other power supply while its not hooked up to a board you care about: I'm not sure it will work lol. I hereby limit my liability of this project.

morkinva: LLC
 
morkinva - your limiting circuit in your diagram is way too limiting.

Typical high cfm 120mm fan is 5-6 watts or ~.5amps of current @ 12volts. The max current your 1000ohm resistor will allow at 17volts is .017amps. Lets for simplicity sake figure the fan to have a static resistance of 24ohm's. Multiply that by .017amps and that gives a .4volt drop on the fan. If you want to use that circuit you will need .5amps minimum through the resistor for a total drop of 1volt, which is a 2ohm resistor that is rated at 1watt. The other resistor is superfluous.

I don't know what fans he is planning to use because each fan setup would need a different resistor value. That is why I suggested diodes because their voltage drop is always consistent.
 
I'm using two Papst 12cm fans. They are rated at 16volts and 3.5w.
Do i need to connect both the negtive 12 volt and 5 volt to the negtive side of the fan and only the postive 12volt to the other side??
 
Originally posted by: cdsonic
I'm using two Papst 12cm fans. They are rated at 16volts and 3.5w.
Do i need to connect both the negtive 12 volt and 5 volt to the negtive side of the fan and only the postive 12volt to the other side??
Click to expand...

The positive lead should be connected to the +5v and the negative lead to the -12v OR (not and) the positive lead should be connected to the +12v and the negative lead to the -5v. This may burn out your fan if it can't handle 17v.
 
Won't positive 12v and negative 5v = 7volts +12 - 5= 7
and positive 5v and negtive 12 volts = -7 volts +5 - 12 = -7
 
Won't positive 12v and negative 5v = 7volts +12 - 5= 7
Click to expand...

NO!!! Because voltage isn't an absolute measurement. It's always measured as a difference, usually between some voltage an ground. SO you would get:

+12 - (-5) = 17 That's why people talk about voltage difference.

+12 - (+5) = 7 So using +12 and +5 gives you 7.

Another thing to watch out for is the current rating for your -5V rail. Usually they have fairly low current rating and you may burn up your supply.
 
ttn1 is very right about those negative voltages current capability. My older 330watt Enermax only has 1amp of available current on either rail. Two big 120's would suck that much up and leave nothing for any other circuitry that needs it. And that is assuming your supply even has that much on those rail.

You should probably just use the normal 12v and plan on buying fans with more cfm.
 
it is just at 16volts they are surposed ot push 159cfm each.

I have two PSU hooked up one for fans and harddrive, cdroms etc and one for my mobo, cpu, etc and my overall temps have gone up by 5c since putting in the second power supply.
 
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