Undervolting exhaust fan of no-brand psu: problems?

PSUs: The source of DC power for all components in the PC & often a big noise source.

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garacs1
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Undervolting exhaust fan of no-brand psu: problems?

Post by garacs1 » Tue Dec 12, 2006 8:33 am

As the subject says, I undervolted the only exhaust fan down to 5V of a no-brand 450W psu, trying desperately to turn down the noise that damn thing makes.

How did I do this? simple and very effective. The no-brand psu had some +5V "spots" not used from where all the +5V wires are soldered to, so I desoldered the red (+12V) wire of the fan, leaving the black earth wire in place, and connecting it to the unused spot. The result is that obviously the fan is running at 5V, and the noise finally was defeated.

My question is, though: should I expect temperature issues from the psu? or can I go with that modification? To my experience, assuming that the pc will not run heavy tasks nor games nor any other thing that should draw huge amounts of power from the psu, even with a so reduced amount of "refrigeration" the psu should work flawlessly. Am I right?

Oh, for those who are wondering: there are no other exhaust case fans. But there is an intake fan in the front side of the case, right in front of the HDD rack: a 92mm PAPST fan running at 7V. I undervolted even the CPU heatsink fan (stock AMD fan) and couldn't notice more than a 8°C rise for the A64 3500+ I am using. Temps are overall very low: 34°C for the case, 31°C for the CPU in idle (temps read from the ASUS pcprobe, so I expect real temps for the cpu to be 10°C higher circa).

Returning back to the psu: what can I expect from it due to the lower fan voltage?

Regards.

Garacs1

Buddabing
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Re: Undervolting exhaust fan of no-brand psu: problems?

Post by Buddabing » Tue Dec 12, 2006 9:10 am

garacs1 wrote:
My question is, though: should I expect temperature issues from the psu? or can I go with that modification? To my experience, assuming that the pc will not run heavy tasks nor games nor any other thing that should draw huge amounts of power from the psu, even with a so reduced amount of "refrigeration" the psu should work flawlessly. Am I right?


Returning back to the psu: what can I expect from it due to the lower fan voltage?
Some fans don't start up at 5v. Make sure yours does.

IMO you are playing Russian roulette with your PSU. It may or may not burn out at any time. When and if it does, it might take other components with it.

If you care enough about the noise, you can afford the money to buy a high-quality, low-noise PSU. Keep the old one for a spare or for folding.

MikeC
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Post by MikeC » Tue Dec 12, 2006 9:17 am

If your read the FAQ for Newbies in the Newcomers Briefing Room, then you'd know to....
Provide full details of your gear and conditions when you ask for advice. Things like a basic component list in your PC, ambient temp in your room, the noise environment (at least a general description) and so on. Temperature readings and noise perception are both extremely dependent on conditions. Being specific and detailed will save time and avoid frustrations for everyone trying to discuss the matter with you.
In your case, since we have no idea of the load your system imposes, there's little we can say.... except that if the PSU fan is the only exhaust, that's very little airflow through the case.

garacs1
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Post by garacs1 » Tue Dec 12, 2006 9:36 am

MikeC wrote:If your read the FAQ for Newbies in the Newcomers Briefing Room, then you'd know to....
Provide full details of your gear and conditions when you ask for advice. Things like a basic component list in your PC, ambient temp in your room, the noise environment (at least a general description) and so on. Temperature readings and noise perception are both extremely dependent on conditions. Being specific and detailed will save time and avoid frustrations for everyone trying to discuss the matter with you.
In your case, since we have no idea of the load your system imposes, there's little we can say.... except that if the PSU fan is the only exhaust, that's very little airflow through the case.
Ok, you are right, sorry for that.

Specs:
AMD Athlon 64 3500+ S.AM2 w/ stock heatsink and fan (downvolted to 5V)
ASUS M2N <GREEN>
ATI X300SE 256MB
Maxtor 160GB S-ATA2
512MB DDR2
DVD-RW
450W no-brand PSU (exhaust fan downvolted to 5V)
Floppy reader
TRUST CR-3300 Media Connect Bay
Intake 92mm PAPST fan downvolted to 7V

I am currently running a prime95 stress test session, no issues whatsoever found up to now (3 hours testing, counting)

Tamb is 23°C circa
Tcpu is 34°C
Tmb is 35°C
+12V @ 12.42V
+5V @ 5.02V
+3.3V @ 3.38V
Vcore @ 1.26V

Cool'n'Quiet installed and working fine (installed drivers, bios option selected)

This is it. If you need some more info, please ask.

Garacs1

garacs1
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Post by garacs1 » Tue Dec 12, 2006 9:37 am

All temperature and voltage readings done via the pcprobe.

jaganath
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Post by jaganath » Tue Dec 12, 2006 9:57 am

Returning back to the psu: what can I expect from it due to the lower fan voltage?
Lower fan voltage = less cooling = PSU runs hotter = PSU dies sooner. It really is as simple as that.

However, your PC uses very little power (<100W) so the PSU could last quite a long time with such minimal cooling.

MikeC
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Post by MikeC » Tue Dec 12, 2006 10:02 am

Moving the intake fan to the back panel and using it as an exhaust might help keep the psu a little cooler. It would tend to reduce the amount of heat that goes through your psu.

garacs1
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Post by garacs1 » Tue Dec 12, 2006 11:21 am

Here are some pics of the case, as it is assembled now:

Image

Front bezel will have covers.

Next pic shows vent area on lateral cover, with funnel placed directly in front of the cpu heatsink fan

Image

garacs1
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Post by garacs1 » Tue Dec 12, 2006 11:24 am

This is what the inside looks like:

Image

The funnel:

Image

The back panel vent hole:

Image

And the small vent holes on the psu casing:

Image

garacs1
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Post by garacs1 » Tue Dec 12, 2006 11:28 am

This is what the psu label reports:

Image

qviri
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Post by qviri » Tue Dec 12, 2006 11:53 am

I would definitely suggest a rear case fan. Trusting the PSU to exhaust the majority of the heat produced with a 5V fan can't be good for the livelihood.

I would also twist the bars separating the intake holes in the PSU 90* to make the holes bigger. In low-airflow conditions, every improvement helps.

Lastly, maybe consider moving the optical drive (and possibly the memory reader) down, and making a duct from the 5.25" slots to power supply intake. Fresh, cold air == good for cooling.

IsaacKuo
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Post by IsaacKuo » Tue Dec 12, 2006 2:26 pm

With all those openings all over the place, I doubt the majority of air is exhausting through that PSU. I'll bet more air leaves various exits due to positive pressure from the loosely ducted CPU fan, as well as that intake fan.

Personally, I've used several no-name bottom end PSUs with 80mm fans undervolted to 5v in various projects. I haven't had any reliability issues so far, but my projects aren't very high powered either. My main problem with no-name PSUs is that they're likely to have weird buzzing or coil noise issues.

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