Quote Originally Posted by Scarlet Infidel View Post
Just looked at those graphs, quite interesting. Its a shame none of the models they have match the ones I'm using.

What I'm interested in, is the massive spike in COP at around 1/8 of Imax. Though there's a huge disadvantage of running any lower than this magic point.

Also, at this point you'd only be pumping around 10w per element (on the type of element I'm looking at) so perhaps a slightly higher current is better in that respect (though still at the peak).


For the closest element to mine, for 20w movement at dT of 10c it will require 7w of power. This is a COP of 2.85 with a hot side of around 33c with cheap air cooling.

As I have 10 peltier modules, I'm looking at cooling 200w load with 70w power to ambient (of course this is best case, there are all the thermal interfaces etc). This seems to match nicely to my previous calculations and real world tests.
I think you said you have 12709's - you can take the 12712 curves at http://www.ferrotec.com/products/the...ail.php?id=115 and derate by 25% to get an idea of where you should go. You can do a quick double check looking at 12708 and 12710 curves, you should be right in the middle but unfortunately the nice ferrotec calculator doesn't have those values and the thermal enterprises curves are harder to read.

If your hot side is 35C, you have more options for low voltage. You can't achieve better than 2.0 CoP with a differential over 15C.

If the small sinks you describe are kind of 'OEM Standard' solid aluminum, they probably have .7 to .8 C/W rating. So using your numbers, you would be throwing off 27W per element, and would see around a 20C rise. If the sinks are a little better, like a decent sized copper base aluminum fin, you might get .4 C/W, which gets down to the 10C differential level.

Let's look at the 3.0 and 2.0 CoP points. For your units, the 3.0 point puts you at about 1.8A, which with 10C differential and 35C hot side puts you at about 3.7V per unit, pumping about 20W for 6.6W in. That's similar to what you were thinking. You coulkd do 3 groups of 3 in series off of a 12V supply and hit the voltage pretty well.

If you go to the 2.0 CoP, you need a pretty efficient sink - you can't do that CoP with over 15C differential. You'll need about 2.6A and 5.1V, pumping about 26.5W for 13.25W in. So efficiency starts to roll off but you get more transfer, and you are at a nice standard voltage. You have to unload about 40W per unit. That would raise your hot side to 15C over ambient with a .4 W/C sink.

Taking the 3.0 CoP and using the series power scheme off 12V, 9 units would move 180W with a total heat load of 243W. If that meets your cooling needs (that would drop a 1GPM flow about .6C), you might be fine.

Taking the 2.0 CoP and running off 5V parallel, 10 units would move 265W which is respectable, with a total heat load of 400W. That would drop a 1GPM flow about 1C, and if your heat in is lower than 265W, you should also be able to achieve some nice low temps.