There is some really imortant information I didn't see covered: the relationships of
Imax, Qmax, and Vmax when a voltage lower than the
TEC's specified Vmax is used as the input. I haven't seen a TEC with a Vmax above
12V but yet *less* than 14.7. Thus, they will all be running *at least* 18% lower voltage than their manufacturer specified Vmax when the PC's ATX PSU is employed. In this example, 24% lower voltage:
Example TEC, IMB Products model# inb127-1.4-1.05
Imax 8.6A
Qmax 84W
Vmax 15.7V
DTmax 69C
ATX PSU 12V
So...
Question #1
If one runs the TEC at 12V instead of 15.7V, does the current (Imax) go up or down as a result? Standard electrical theory would lead me to believe Imax would increase to maintain Qmax, given a decrease in Vmax (V * A = W). However, I don't know enough about the design and behavior or TECs, thus the reason for the quesiton. I.e. will a 12v input in this example make:
Imax = (12/15.7) * 8.6 = 6.57 Amps?
Or will it increase to 11.25 Amps? (since the TEC's total draw is apparently 15.7V * 8.6A = 135W, due to the TEC's inefficiency)
Question #2
With the 12V ATX PSU input will:
Qmax = (12/15.7) * 84 = 64.2 Watts?
Or will it stay at 84 Watts?
Question #3
If the GPU thermal output at full boogie is 50W (this is probably way too low an estimate for the top end nVidia and ATI GPUs--68xx/78xx, x18xx/x19xx, but probably about right for 66xx/FX59xx/9800/x800/etc), then will:
Delta T = (1-(50/64)) * 69 = 15.09 degrees C?
Or will it be 27.92C, if Qmax stays at 84W?
Assuming Qmax does decrease when using a 12V input, at an ambient case temp of 25C, the cold side of this TEC, assuming a 100% efficient water or air cooling system, would be 10C (or 50F). Anyone know a ballbark figure as to what % higher the GPU core temp typically is compared to the TEC cold side plate?
In my personal setup, my current loaded GPU temp on my FX5900 is in the high 50C range (maybe low 60s), and mid 40s idle. So, I could expect what, 20-25C under load now, or will core temp not be that much higher than the cold plate? That's a pretty decent drop, but still not anywhere near freezing, which I would think would be an absolute requirement for major overclocking, which is my goal in building my TEC.
Even though it would cost me a new higher amp 12V rail ATX PSU, I'm really hoping the answer to Qs 1 & 2 are that higher amps will be drawn and an 84 watt Qmax maintained, because this would yield a Delta T of 27.92, an additional 13C drop, which will give me a cold side temp of -3C assuming 100% cooling efficiency (not likely, but maybe close).
If lowering the voltage lowers all these other parameters, I guess I'll just have to drop some cash on a dedicated variable voltage PSU, although I'd really really like to avoid it, as I'm designing an air cooled, *compact* (compared to liquid that is) solution to mount directly to the card. Once my Qs are answered (hopefully accurately, and swiftly), I can order my parts and get to work.
It should be a fun process, probably time consuming, potentially fruitless. However, I've not read of *anyone* doing an air cooled pelt for GPUs. I like being unique, and "doing what *they* say can't be done".
Besides, quickly evacuating a paltry 185-220 watts with air over fins shouldn't be too difficult.
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