Have a 140mm papst 6424. Can I use it?

RonG · Post by **RonG** » Sun Feb 27, 2005 9:47 pm

I was walking through the surplus department at Princess Auto, and I came across two 140mm fans, which immediately gave me some cooling ideas. One was a Chinese made ADDA 120ac.34A fan. I've already tried it with a fan speed control, and while it pushed a lot of air at half speed, it buzzed and clicked, so I'm going to return that one.
The other is a Papst 24vdc 1.1amp 26W fan. I have an Antec Truepower ps, and it comes with a fan power connector. When I connected the fan it ran at the speed controlled by the ps (which I assume is the speed at which it runs its own fan), and it was pretty quiet, but it did take a little while to start up.
When I connected it to a regular molex connector it ran too loud, but it started immediately.
I have an amd64 3000 in a k8v-x motherboard, a ti4200 gf4 video card cooled by a zalman heatpipe/heatsink and a 120mm antec fan, a zalman 7700 cpu fan, 1 wd 200gb hd, 1 seagate barracuda iv 60gb hd, an audigy soundcard, all powered by a 380w Truepower ps. This is cooled by a 120mm Acuflow chinese 120vac fan at about half speed, but the system isn't powering this fan.

My question is can my system handle the papst fan? And if it can, will a fan speed controller also handle it if it powered from a regular power connector?

sthayashi · Post by **sthayashi** » Sun Feb 27, 2005 10:07 pm

I don't think any fan controller can handle a 26W fan. Even at half voltage it's drawing around 10-13W, more than what most fan controllers can handle.

The power supply should be able to handle an additional load like that though.

RonG · Post by **RonG** » Sun Feb 27, 2005 10:09 pm

Can I use an ac fan-speed control?

Gholam · Post by **Gholam** » Mon Feb 28, 2005 2:39 am

IIRC, Sunbeam Rheobus is rated at 20W per channel, which makes it a possibility. On the other hand, it's been known to burn out quite often, although that might not be due to high loading.

EricTerminator · Post by **EricTerminator** » Mon Feb 28, 2005 4:36 am

Hi !

I just want to correct sthayahi ; when you use half the voltage, the consumption drops to 1/4 of the original, about 6.5W.

It's because of the rule of Ohm, U=RI. If U is the half, R is constant, I must be the half too. And the formula for the power is P=UI, so, half of the original U multiplicated by half the original I gives 1/4 the original P.

See you

~El~Jefe~ · Post by **~El~Jefe~** » Sat Mar 05, 2005 4:12 pm

EricTerminator wrote:Hi !

I just want to correct sthayahi ; when you use half the voltage, the consumption drops to 1/4 of the original, about 6.5W.

It's because of the rule of Ohm, U=RI. If U is the half, R is constant, I must be the half too. And the formula for the power is P=UI, so, half of the original U multiplicated by half the original I gives 1/4 the original P.

See you

wow thats some cool geeky crap batman

nice info, makes me consider something i was going to do with remote sorta cooling setup.

JanW · Post by **JanW** » Sat Mar 05, 2005 5:04 pm

EricTerminator wrote:when you use half the voltage, the consumption drops to 1/4 of the original

Ohm's law would apply if the fan motor could be modeled as a purely resistive load. But it looks like that's not always the case.

Gorsnak · Post by **Gorsnak** » Sat Mar 05, 2005 5:29 pm

JanW wrote: Ohm's law would apply if the fan motor could be modeled as a purely resistive load. But it looks like that's not always the case.

Well, it isn't, but the point remains that the fan won't be drawing half the watts at half the volts. When you cut the voltage in half, current will be cut approximately in half. Approximately, because at the new level of current, the fan's impedance will likely be different than it was at old level, so you can't just ignore the resistance variable in Ohm's Law like you could if the fan could be modeled as a purely resistive load. Still, in this case it's highly unlikely that "half the volts will give you a quarter the watts" will be misleading as a rule of thumb.

JanW · Post by **JanW** » Sat Mar 05, 2005 6:26 pm

If you bet your M/B fanheader or your fan controller on the estimate of a fan's power consumption, then that estimate better be fairly accurate. 26W/4=6.5W might be safe, whereas 26W/3.3=7.9W might not. That factor 3.3 is the reduction in power consumption you get when going from 12V to 6V on the Panaflo measured by cpemma in the post I linked to, and for all I know, RonG's fan could scale even less favourably. That is precisely the range of power consumptions where that "small" difference matters. My point was not that stayashi's estimate was right (but it had the merit of being conservative). My point (which I could have made clearer, I agree) was that you need to be careful with this kind of estimates.

EDIT: wording