TEC V and A question

[eX&TriC]

If you take a 24V TEC 12A and put
12V on it does it then use 6A or still 12A??

24V 12A = 100% VA
12V 12A = 50% VA
12V 6 A = 25% VA

I want to use a drift 0.8 172W on 12V and
cool a GF4 with it. I need 80W effective cooling
on 40 x 40 mm. I already used to the search to
find out that it would give me 86W but I thought
that there was a linear correlation between V en A
with TEC's. But it seems to be very strange that
with 25% power consumption I would get still 50%
cooling power... Or is this an example of the fact that
tec are in efficient @ high A...

greetz and thnx

[Miss_Man]

It uses roughly 6A at 12v.
Yes, you get around 50%, actually I think more like 40%, cooling as its efficiency increases until around 18V where it drops off and does not provide much more cooling with increased voltage.

[eX&TriC]

so with 25% powerconsumption 72VA I get +-50%
coolingpower ...

if 18V is the most effective then cooling would be higher
than 40% at 12V no?

[Miss_Man]

I dont have the graph with me, but lets say you get about the remaining 10% of the 172w after 18v. That means you have 90% of it at 18v, and bearing in mind cooling improves a lot during the 14-18V stage, which can make up about 30%, that makes 12v ~ 40% quite believable.

[Brad]

pelts are more efficient at lower voltages, but of course the more voltage you put through the more cooling you will get. At 12v at 172w will give you around 43w of cooling, but this isn't aa really accurate figure, anywhere up to 50w could be accurate.

you'd be better to get a 156w 15v pelt and run it at 12v

[eX&TriC]

"At 12v at 172w will give you around 43w of cooling..."

I'm confused ??

the 172W is the most efficient at 18V but at 12V i would only get
40W. I thought the COP went up

"Low power consumption - While this may seem oxymoronic for a thermoelectric (TE) system, my goal was to minimize power consumption. This was realized through the use of a high-wattage TE operated at (0.5)Vmax (12V, in this case; thermoelectrics have higher COP (coefficient of performance) at lower voltages, which equates to higher efficiency). In fact, the Melcor 'CP 1.4-127-045L' (Imax=8.5, Qmax=72, Vmax=15.4) operating at 12.0V, compared to the Drift-0.8 operating at the same voltage, will have inferior performance and at the same time consuming more power." from http://mozcom.com/~ronnieg/system/pelt.html


Please would anyone confirm 100% sure what happens
if you run a 172W @ 12V

....24V...172W....12A

A).12V...86W....12A
B).12V...86W....6A
C).12V...43W....6A

tnx

[Miss_Man]

A is out because the Amperage drops linearly from Vmax as V goes down. B is also out because 12 x 6 is only 72 and thats the power it consumes, and since pelts are definitely not so efficient, the figure 86w is too far off.
It would be like what Brad has said, somewhere ~ 50w, since it consumes around 72w of electricity at 12v.

[eX&TriC]

you can feel that there is something inconsistent here.

if you run a peltier 172W at 18V you get the best performance
if you run a peltier 172W at 12V you only get ~50W ??

12V= 2/3 of 18V
so you would only get 1.5 times 50W = 75W at 18V ???

the COP goes UP if if the voltage goes DOWN (TEC are more efficient at low voltages) so you gain cooling ability relative to
the amount of power used and not the other way around...


this guy used a tec 12V 6A 75W as load for 3 pelts 172W in a T at
8V......134W/3 = 44.66W
10V....185.1W/3= 61.66W
12V....242W/3= 80.66W
13V....306.9W/3 = 102.3W

from http://homepage2.nifty.com/masamoto/DATA10.html
is in japanese but babelfish will translate it

[Brad]

I didn't say anything exact hehe. but 40w - 50w is approximately right

[Miss_Man]

No, its a curve you know, you can't just exponentially calculate that way. 1 more V can get you a lot more cooling when you're at 12V then when you're at 18V, if you get what I'm saying. Its a lot easier if I could link you to the graph, but I can't remember where I saw it.

[eX&TriC]

I know what you mean.

I know now that TECs are relatively more efficienant at low voltages. So if you raise the voltage the amount of watt gained is decreasing or you got a curve like the black one:
What you are saying if you only get 40W is that the blue curves apply to the TEC
so that a little gain in voltage in the low part 2-3 gives you a
smaller raise in W than from 12-13V Which you are denying later
in you post saying "1 more V can get you a lot more cooling when you're at 12V then when you're at 18V" So the black curve applies and you can never have +-50W (2/7 of 172W) at half voltage 12 (1/2 of 24V)



My confusion comes from the fact that

If you drop the V in half you also lower the A so you only
get one quarter of the watt wich would be on the blue curve.
just like Y=X^2 with x>0 But how do you explain the fact that
tec are more effective at low voltages and that 75% is the
best ratio.

I hate this I need TO KNOW

[Brad]

lets say a 172w pelt is running at full voltage, it uses 278w, and can remove 172w. Lets say it's running at 12v, it uses 69.5w, and can remove 50w of heat. which is more efficient?

75% isn't the best ratio, it's just a good combination between cooling and power use