Quote:
Originally posted by Butcher:
you'll probably need to heatsink the transistors, they'll have to sink any power the pelt doesn't get, so at 12V from 24V you drop 12V over thr transistors, at 7 amps that's 84W on the transistors...
70C is the approximate target for thast sort of electronics so a HSF with a rating of say 0.7C/W would do on the transistors, that's fairly hefty if passively cooled but something with a fan it's similar to a low spec cpu cooler.
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OK, let me see if I've got this straight. An electronics genius, I'm not. I'm assuming a relatively linear relationship between the voltage the peltier sees, and the amperage it draws. Probably not the best of all assumptions, but in the absence of curves, it's all I have.
If my controlling voltage to the transistors yields about a 6v output, then I've got the following to deal with:
Peltier (11.3A @ 24.6V) wants about 3amps (more or less).
That means there is a drop of 18volts x 3 amps across the transistors, 54W of heat I need to get rid of.
If, on the other hand, my controlling voltage allows 22V to pass:
Peltier wants @ 10.5 amps, therefore, the drop across the transistors is 2V x 10.5 amps, 21W.
I need keeping in line on this, as it's counterintuative to me that the heat dissipated in the transistors will start low, go high in their "sort of on"/linear response state, and then drop again when they're saturated.
So far, my calculations suggest that the peltier will be running at about 12-15V on a normal basis.
Thanks for your help, Butcher