This Peltier cooler just emerged from a pile o’ stuff on the Electronics Workbench, so I combined it with a scrap CPU heatsink (using plain old water as “thermal grease”) and fired it up to get some quick numbers for future reference.
It draws 3 A (the bench supply’s current limit) at 5 V. The cold side got down to 19 °F with the hot side at 75 °F: ΔT = 56 °F.
That’s with zero thermal load, other than whatever arrives from plain old air and those two plastic clamps. It looks like a nice one, so it’s maybe 10% efficient and could pump a watt, barely enough to cool a simple circuit.
Freezes a drop of water just fine, though.
The I-V curve is nearly bar-straight over the first five volts: call it 620 mΩ. The thing would draw 7.5 A at 12 V, call it 90 W, and could pump maybe a whopping 9 W from the cold side.
Actually getting good numbers would require some serious work that I’m not up for. In particular, everything has a serious temperature coefficient, so nothing would be the way it looks. I have doubts about the efficiency guesstimate; I’d like to actually measure that sometime.
But it confirms my opinion of Peltier coolers between hundred-watt CPUs and water-cooled heatsinks: pure delusion.
The Smell of Molten Projects in the Morning 
Wait, people are mounting Peltier elements on top of their CPUs? I’ve never seen that. :P
In the privacy of their own basements, they’re up to no good…
My buddy Eks gave me a bag of ancient Peltier coolers with some penciled notations that indicate the nominal cooling capacity is a bit under half the input power. The data sheets suggest that’s with no temperature differential across the elements, which isn’t particularly useful.
I could gang ’em up to cool the basement and heat the hot box disinsector, I suppose…
You are thinking about it backwards :-) Peltier coolers make better Peltier heaters than coolers; they put out more heat than they take in as electricity!
– Steve
*facepalm*
Of course! Why didn’t I think of that?
If I clamp a dozen of ’em in series, I can build a smelter…
Looking through Wikipedia it seems that it’s known as a Peltier element or module in most languages, rather than a Peltier cooler (although I suppose light cooling is its most typical use, at any rate :P).
Yeah, when you need heating, you have plenty of cheaper and more effective ways to get it done…
Bah, humbug! Efficiency is for the weak. :P