Re: Varying pump speed possible?
 

Downside of PWM: Tach output probably won't work (or if it does, it'll most likely give the wrong reading).

mx: a potentiometer is usually used to form a potential divider such that the centre connection can deliver a variable voltage between the voltages on the other two pins.

If the psu and the miniNG have a common ground (likely) you may well be able to just hook the one directly to the other. You may need a pull down resistor or current limiting resistor depending on the configuration of the PSU. Can you post a circuit diagram or pics of the circuit board?

Re: Varying pump speed possible?
 

How can I find out if they have a common ground?

I don't have any circuit diagram but here's a couple of pictures on the potentiometer area. The switch on the back overrides the pot and locks the output voltage to 13.8V.
http://img157.imageshack.us/img157/5766/front9dr.th.jpghttp://img225.imageshack.us/img225/5717/back8cd.th.jpg

The last time I tried to figure out how to do this I did some measuring but I didn't really know what to measure. :doh:
But non of the three wires seemd to be connected to ground?
Should I take a photo of something else or maybe measure something?

Re: Varying pump speed possible?
 

Common ground - if the PSU ground is connected to the AC line ground they do (since the computer's ground will be).

Kinda difficult to tell what's what there as it appears to be a multilayer board.

BTW, why are you using such a huge PSU for pumps? :p

Re: Varying pump speed possible?
 

I don't think it's a multilayer board, but yeah the photos don't help much. :)
I wish I had a circuit diagram!

It's my peltier psu. Varying the pumps voltage is just a test, if it works I'll use the same metod for the pelts. I want to vary the TECs voltage to minimize condensation and save some electricity (money). And if I find that varying the pumps speed automatically depending on temperatures is any good I might get a second smaller psu to controll them, it's nice to be able to run them on 13.5V sometimes. But mounted /w anti vibraion rubber things inside my sound dampened case I can barley hear them anyway so I doubt it.

Re: Varying pump speed possible?
 

You could try just connecting the centre wire from pot to the miniNG (or another suitable voltage source if you don't want to risk the miniNG) and see if it can vary the output voltage.