Maker Pro
Maker Pro

Calculating temps using a Peltier

D

dan

Jan 1, 1970
0
I'm trying to calculate some things here, and I'm wondering if I got
it correct. To figure out the hotside of the peltier, here's what i've
been using...

Th = Tamb + (C/Watt)(Qc+Pin)

Th = Hot side
Tamb = Ambient temperature
C/Watt = Thermal resistance of heatsink
Qc = Load (in watts) on cold side
Pin = Watts peltier is using

To get the C/Watt i'm using

deltaT = DeviceTemp - Tamb
C/Watt = deltaT / Qc

deltaT = Temp difference
DeviceTemp = Temp of the device to be cooled

So to get the C/Watt, let's say I've got a device outputting 70 watts
of heat, with a temp of 46.1c and an ambient temperature of 29.4c.
I'd do:

deltaT = DeviceTemp - Tamb
C/Watt = deltaT / Qc

deltaT = 46.1 - 29.4
deltaT = 16.7
C/Watt = 16.7 / 70
C/Watt = 0.238

Correct?
Now that I got the C/Watt, I can do the calculations to get the Th.
Using the same values from above, and using the 169 watt peltier from
http://www.dangerden.com/mall/Pelts/peltiers.asp as an example....

Th = Tamb + (C/Watt)(Qc+Pin)
Th = 29.4 + (0.238)(70 + 169)
Th = 29.4 + (0.238)(239)
Th = 29.4 + (56.882)
Th = 86.282c

So the hotside of the peltier would end up being 86.282c (all
calculations are done in celsious). Right?

Now, to get the cold side, I've read about looking up the
specifications for the peltier. And looking for a permorance graph of
some sort from the peltier manurfacturer to show the cold side temp at
a certain hotside temp. But then I ran across this formula for getting
it..

deltaT = (1 - (heat load/max cooling power))*max temp difference

heat load = CPU's heat output in watts
max cooling power = Maximum peltier rating in watts
max temp = Peltier's maximum temperature rating, in degrees C.

so i guess it would be
deltaT = (1 - (Qc/Qmax))*deltaT max

Using the 169 peltier from that page as an example and using above
values (70 watts output from device) I do...

deltaT = (1 - (70/169))*69
deltaT = (1 - (0.414))69
deltaT = (0.586)69
deltaT = 40.434c

40.434c would be the deltaT the pelt would be using at that current
temperature. So to get the cold side temp, all I do is subtract 40.434
from 86.282 (gotten from above) to get 45.848c, the temp of the cold
side of the peltier. Correct? Sorry for this being such a long post,
just trying to figure this out... Thanks for any help.
 
Top