Quote:
Originally Posted by ChielScape
also, isnt it the current that determines the Q moved?
and is it the current or the voltage that determines the deltaT?

right well I will answer your questions round the other way...
I hope I don't fudge this for you...this is the easiest way I can answer at the moment.
To start an operating point is defined as the voltage you have chosen to apply to the TEC and the corresponding current value in amps from a performance chart.
Delta t (Dt) is the temperature difference, most often quoted in ÂºC, between the hotside and the coldside.
It depends on 3 things a.) the cooling applied to the hotside b) the load applied to the coldside and to a lesser degree c) the operating point (volts/amps.) At full power (the highest operating point) Dt max applies and this is usually, for most single stage TEC's, in the region of 68ÂºC72ÂºC. As the operating point falls so does the Dt max.
If you increase the load to the coldside without altering the cooling on the hotside the Dt gets lower. If you increase the cooling on the hotside without altering the load on the coldside the Dt also gets lower.
One of the easiest ways to alter the Dt is by altering the hotside cooling.
The lower the Dt the nearer you get to the maximum pump for that operating point.
Bear this mind while i answer the next bit....
Qc is the amount of heat pumped at a set operating point/temperature.
Qc is defined by the following formula  QC = 2N [α I TC  ((I2 Ρ) / (2 G))  κDT G]
what a mouthful !! Let me simplify it.....
Qc is altered by a) the temp of the coldside b) the current at the operating point c) the area of the TEC and finally d) the
Dt
When you are running a TEC you usually have a set load (use the max TDP of the CPU.), a set operating point and of course you can't alter the physical size so basically the first three requirements for Qc are static and don't alter which brings us to the last thing, the Dt.
Ignoring the fact the Dt max alters with the operating point, the DT is affected by the load applied to the coldside and the cooling applied to the hotside.
As I have just said the load to the coldside could be considered static so the only movable thing is the cooling applied to the hotside. Which is why cooling the hotside is so important.
Qcmax is the maximum heat pump obtainable at the maximum operating point (full power.) when the Dt=0.
So when you set a lower operating point there is a reduced maximum pump available which is equal to when the Dt=0 (maximum 100% cooling of the hotside so it equals the coldside.) if by altering the hotside cooling you increase the Dt you will decrease the heat pump downwards from the value determined as maximum by the operating point.
To clarify if your TEC has a Qcmax of 200w and maximum operating point of 16volts/8amps and your chosen operating point is 12volts/6.5amps If for instance the maximum available pump (Qc) at 12v with a Dt of 0ÂºC is 150w...It might be that your Qc at a Dt of 20ÂºC is 135w but if your Dt is 40ÂºC your Qc might only be 95w. You can only reliably see this on performance charts.
EDIT  As in interesting point to note....If you power a TEC, any TEC, at 50% of maximum current if the Dt is 50Âº or more the TEC will pump virtually nothing....5% Qcmax or less.
Edited by zipdogso  4/28/09 at 7:26am