Hobby electronics question

Brian The Snail · 23 Oct 2012 at 20:35

I'm making a fan for my woodburner. It uses a thermoelectric cooler, AKA TEC, AKA peltier atached to a heat sink to create a temperature difference to generate current to power a small fan.

When I put current into the TEC, one side gets hot and the other gets cold. If I'm putting heat into one side I get current out.

I'm mindful of damaging the TEC by putting too much heat in. Which side should I put against the heat source? The side that gets cold when I put current in or, because I'm getting current out, the hot side?

I'm thining it's the hot side. Advice appreciated.

Regards,
Andy

geuben · 23 Oct 2012 at 20:41

Do you have a part number for the TEC you are using? Some more details would help.

I don't know if TECs are polarised, if not then the side that gets hot will change depending on which way you are applying the current.

To generate most power you want the biggest temperature difference. I would put the hot side against the heat and the heatsink on the cold side.

Putting too much heat in is tricky, without specific details of the TEC, the temperature you will be subjecting it to and the efficiency of your heatsink it's impossible to say what you will do to the TEC.

Brian The Snail · 23 Oct 2012 at 20:55

Thanks for the reply.

The unit is a TEC1-12704. A PDF spec is available here

I've got a massive heatsink to help with the temp diff.

I was experimenting at the weekend and am able to generate about 1.3v which is more than enough for the little motor.

geuben · 23 Oct 2012 at 21:04

The data sheet says it is polarised so you will need to connect it the correct way around.

How hot does the point your going to mount it to get? what is the ambient air temperature in the area the heatsink will be?

Operation or storage module below 100℃

Would indicate that you don't want it getting that hot.

The data sheet isn't great. There is a table with no headings for example.

23JMZ07 · 23 Oct 2012 at 21:09

I personally don't think you could get an adequate difference in temperature between the hot and cold side consistantly and safely for it to work. I could be wrong though.

Brian The Snail · 23 Oct 2012 at 21:10

geuben said:
How hot does the point your going to mount it to get?

Very. Measured with an oven thermometer at 125 C.

geuben said:
what is the ambient air temperature in the area the heatsink will be?

Guessing around 70 C.

geuben said:
The data sheet isn't great. There is a table with no headings for example

There's ebay for you.

Because they are reasonably cheap I may just chance one.

Thanks again.

geuben · 23 Oct 2012 at 21:14

Brian The Snail said:
Very. Measured with an oven thermometer at 125 C.

Guessing around 70 C.

There's ebay for you.

Because they are reasonably cheap I may just chance one.

Thanks again.

I was going to suggest just winging it if it was cheap.

you might want to look at some insulating material between it and the heat. 125 degrees is above what the datasheet would suggest.

Brian The Snail · 23 Oct 2012 at 21:55

Cheers.

trojan698 · 23 Oct 2012 at 22:24

TECs pump heat from one side the to the other. The performance graph should be used to choose one that's appropriate. you need to calculate the heat you're transferring in Watts, and use a TEC that will provide it. Most TECs advertise a temp difference of ~70c but this is not especially relevant, as you're pumping a quantity of energy, not a temperature.

Check the datasheet - it should provide a graph but in my experience most dont.

Do you have any idea of the wattage (in heat) u want to pump? Multiply this by 1.5x to get an efficient (cost) TEC.

Good luck, they a nightmare to figure out, and even the graph and calculations wont provide accurate results.

Edit - Just reread your opening post, and attaching it to a heatsink will hinder the heatsinks operating, and may kill the chip you're cooling as it provides a layer of insulation.

bitslice · 23 Oct 2012 at 22:34

I'd guess if you apply a current through it and side A gets cold and side B hot, then to produce a current using heat then you would have to reverse it and heat side A and cool side B.

Which from the diagram I think the side with the soldered leads should be attached to the stove (suck it and see really

)

The output depends on the temperature differential, so if you could insulate the hot side and vent the cold side to the outside somehow, that would be ideal.

To keep it below 100degC and stop the solder melting off you could boil water and pipe that to the device?

trojan698 · 23 Oct 2012 at 22:41

at very least youd need a heatsink on the hotside of the TEC