Quote Originally Posted by bds71 View Post
OK - some things are becoming clearer, but some things just aren't quite clicking - hope i don't sound like a broken record here (especially on the last part) - eventually, i'll just click the "i-believe" button and that will be that....but for now, i want to take another stab at it....




you lost me - current follows voltage: by decreasing voltage, you will decrease current. whether you reduce UMax with a PWM, or by putting 2 TEC's in series, or simply by putting a resistor/potentiometer in front of the TEC the current should decrease proportionately with the voltage??



increasing QMax is a good thing, yes??



this does not compute: 35*20=700; UMax=403 w/dT=67. dT is reached at UMax, not PMax?? question: if i applied 24V@17A (ie:~400W - UMax) would i hit QMax? <confused>



decreasing input voltage decreases dT. increasing cold side decreases dT. all things being equal, i don't think the TEC can distinguish between the two methods so CoP should be the same regardless how its done?



at idle, the situation would be as you state - the radiator would be adding heat to the system (assuming TECs would normally operate below ambient). but at load you have more heat coming from the sources than you do being input from ambient air cooling of the rads (ie: the amount of heat being generated by all the sources - in my case 2x OC GPUs and an OC CPU) would bring a normal water loop above ambient. at **that** point the TECs are adding to the efficiency of the cooling loop to maintain ambient - ie: the radiator is no longer adding heat to the system, but hepling to take heat out of the system. once you reach equalibrium (ambient) the radiator no longer acts as a heat source. at that point it creates a base-line for the TEC to hit. and with the low dT you can easily maintain the hotside within 2-5C of ambient.

i think your scenario assumes that the TECs would be able to **hold** subambient even under load (which is what we all strive to accomplish). in that case, yes - the rad would be adding heat to the loop. (sorry, i'm just working through this as i type this lol)....let me get back on this...more to follow - feel free to comment on previous remarks!!

note: if anyone else wants to chime in on the discussion (keep bashing to a minimum please) please do!!


you lost me - current follows voltage: by decreasing voltage, you will decrease current. whether you reduce UMax with a PWM, or by putting 2 TEC's in series, or simply by putting a resistor/potentiometer in front of the TEC the current should decrease proportionately with the voltage??

right lets use this tec as an example
243 Qmax
15.2 Umax
26 Imax
Pmax is therefore 395watts

if you apply Umax(15.2) then amps will Be Imax (26) and Pmax will be consumed (395)

50% PWM Current while applying Umax will be 15.2v * 13amps so consumed power is 197.5watt

If you apply 50% of Umax or 7.6v then amps is 11.19 so watt used is 85watts



If you bin the extra complexities of a TEC right now and just use ohms law for a given resistance then the same is true

Resistance of 5 ohms with 12 volts = 2.4 amps and therefore wattage is 28.8 watts

if we then 50%pwm (only allow it to draw 1/2 the current it wants to draw) the current or apply 1/2 of it we get 5 ohms 12v and 1/2 of 2.4amps (1.2) so wattage is 14.4watts

However if we apply 1/2 the volts 6 to a 5ohms resistance we get 1.2amps for a wattage of 7.2watts


SOO no matter what you do you should always apply the lowest input voltage as possible for maximum COPs




increasing QMax is a good thing, yes??

YES