Does a pelt need it's own psu?

[Rob Cork]

I think I already know the answer to this, but I just want to check anyway cos I've never used a peltier before and I'm a little fuzzy on them.

I quite fancy the idea of pelt cooling at some point, as my Tbird's starting to get a little warm at 1680MHz and 2.1V - that's putting out around 120W I think :) I reckon with 2.2 or 2.3V and better cooling I could push towards 1800...

Obviously I'd have to use a 172W pelt - I was just wondering whether it'd be possible to have one really high-powered psu (say 530W) and run everything off that? I suspect not, as it'd probably hopelessly overload the 12V line, and I probably wouldn't really have 530-172=348W of power left anyway. I ask because I can't fit another psu in my GW802, and there's absolutely no way I'm switching to another case after only just getting this one together (spent about 2 months planning + modding it).

I expect the answer would be 'no' - if it is, does anyone have any ideas fro cramming an extra psu in? Dunno whether you can get small ones for rackmount servers (probably hideously expensive), or mount an AT psu outside the case... any suggestions? There must be some people pelt cooling with 2 psus and a 1-psu case out there... :rolleyes:

[Thelemac]

With a 172V pelt you'll actually want to get a 24V PSU as that is generally the required voltages on them. So using one PSU really isn't a good idea at all due to voltage requirements.

I don't know much about those kinds of PSUs, though, as I don't currently have one, so I'll let others go into the details of them. :)

[Phil]

I agree with Thelemac, the more powerful pelts use higher than normal voltages such.
Any way even if you could find a 12v pelt, the 530W enermax has a 288W 12v line, so that would leave you 116W for the rest of the system, which though probabally fine for now, with more and more power hungry vid cards and cpu's it may not be long until it is inadequate. then theres the heat to consider from the psu, an enermax is about 70% efficient, so that 172W load would in it's self create another 80W or so of heat on top of what is being created by the power usage of the other components.

[Colin]

For a 172 watt pelt a seperate 24 volt PSU is a must. Most switching PSUs have a trim pot to adjust voltage down to around 22 volts. The better HAM radio PSUs will allow for more adjustment. The 172 watt pelts I have played with had a sweet spot of 20 volts.

With 120 watts of heat, I think two 120 watt pelts would be a better choice. 120 watts from your Bird will be tough for a single 172 watt pelt to handle.

[Phil]

I don't think peltiers are really a good choice for cooling todays chips, it was ok when chips only threw out like 30-50W and then an 80W peltier on top would mean you only had to cool 110-120W, but with todays oc'd tbirds throwing out more than 100W and then with a 170W pelt thats 270W of heat that the waterblock must cool. I think using a chilled medium such as a vapo chill or chilled water is a better option.

[dimmreaper]

Originally posted by Phil
I don't think peltiers are really a good choice for cooling todays chips, it was ok when chips only threw out like 30-50W and then an 80W peltier on top would mean you only had to cool 110-120W, but with todays oc'd tbirds throwing out more than 100W and then with a 170W pelt thats 270W of heat that the waterblock must cool. I think using a chilled medium such as a vapo chill or chilled water is a better option.

Actually Phil, your math is off a bit here mate.

The heatsink/waterblock does not just have to cool Qmax+CPUheat

The heatsink/waterblock has to cool the Qmax+the ammount of electricity the peltier uses, as all of the electrical current it uses is converted to heat in the peltier process.

So a 172W peltier requires you to get rid of 449.98W when running at full Vmax and Imax!!!!!!!!!!

[Rob Cork]

Hehe, yep, thought it'd wouldn't work :rolleyes:

Cheers for the info people - I'll have to come up with some other way of cooling my tbird, or just be happy with what I've got. Maybe I'll start thinking about changing my waterblock now - still got the original Maze here from DD, maybe the Maze-2 or Swiftech MCW462 would help... hmmm :)

*EDIT* Does anyone know how to calculate the Wattage my T-bird is chucking out at 1680 (12x140) and 2.11V? I have the original version of Radiate but it doesn't go high enough, so I'm just sort of guestimating. I have Radiate II but I get an error message when I try a Web Update to get the processors.dat and coolers.dat files :(

[Phil]

I have radiate 2 and I work it out as 125.6W in that, it crashes my computer when I try the web update :)

[Rob Cork]

Originally posted by Phil
I have radiate 2 and I work it out as 125.6W in that, it crashes my computer when I try the web update :)
Yep, I found this formula in that article on cooling at amdmb.com and used it to calculate it myself:

CPU POWER = POWER AT STOCK SPEED x (CPU MHZ / STOCK MHZ) X (VCORE / STOCK VCORE)squared

I make it 126.9 with that. Cool - 127W and still only 21C above ambient - nice :)