As I have learned from RichW here, the power curve for peltiers is not linear, but quadratic...you cannot simply say, "ok, i'm giving the peltier half the power, and it should be able to pump half the heat"...
quadratic refers to exponential change...
to give you an example, for testing, I hooked up my 172W peltier to my 12V power supply(ATX), and it didn't even warm my hand...suggesting to me to have been pumping maybe 30-50W at maximum...
The 156W peltier, according to logic, would provide approximately 124W of pumping power, ASSUMING, that the power supply can provide the appropriate amperage(minimum 15A in this case, since initial draw is more than constant draw)...
having said that, I actually put my 156W to the test...I hooked it up to my new variable 12-15V power supply which can power up to 32A continuously, and 35A surge...at 12V, the peltier was drawing 12.5A consistantly (150W)...hrmm...interesting
at 15V, the peltier is drawing 15A consistently(225W)...wait a minute...hold the phone...how can this be???...
What this means, (and i've verified with Tedist) is that the advertised Qmax is wattage at "maximum efficiency", hence the "max" subscript...since it has been determined that peltiers run at maximum efficiency under 75-80% of full power, it stands to reason that I would be getting Qmax while only providing 12.5A, 12V...
Basically, because of diminishing returns, any further power I give this peltier above 12V 12.5A, reduces efficiency...yes, it can pump 200+ watts of heat, but it is itself generating so much more heat that would be operating with gross inefficiency...
I decided to test cold side temperatures...I held a bag of ice to one side of the peltier, and a rag to the cold side(once I held the cold side directly, and had to "peel" my hand off of it, because it froze)...I got below zero temps on the cold side at 12V, but when I pumped it up to 15V, the temperature reading began to rise...
keep in mind that my temperature readings were erroneous across the board, because the peltier was not sealed, so the probe was pulling heat from the surroundings...but since it's the same compromise at both voltage, the result is the same...higher than 12V on the 156W peltier reduces efficiency...BUT ONLY if you are providing the appropriate current...you must be aware that if you are running this off of your ATX supply that is running your computer, your 12V line probably only has 8-10A left to share for your peltier, if you are using something like the Enermax 430, which provides 12A of power...this will underpower your peltier, and make it mad at you, heh...it will try to draw the current it needs anyway, and your power supply will suffer from it...
bottom line...remember that Qmax is already advertised at maximum efficiency...I have detailed what that is for the 156W peltier from Tedist...but for the 172W and others, I am not sure, as I have not done proper testing with a 18-24V supply...but I am guessing max efficiency would be around 18V, 10A...
[This message has been edited by Cablepro (edited 02-16-2001).]
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