DC Electronic Load for peltier element

[pilsebob]

hello.
I am working on a peltier generator for my cabin. In wintertime there is little sun to charge the 12 volt batterybank. I know that peltiers produses very little power so it will be a small triclecharge when I got the woodstove going.

I have gotten a lot of different peltier elements to find the best for my use but testing has been hard. I have gotten a stable heat rig going but need to messure the power prodused. I was thinking of bying a Electronic Load (with computer interface for logging). I wonder if this will do the trick and if anyone could recommend a good alround Electronic Load that's not to expensive.   

best regards
Pilse

[pilsebob]

I have seen the EEVblog ep 281 with the BK Precision 8500 and it looks very nice.
I would ofcorse use the DC load on other projects but 1000 dollars is a bit much.

[mcinque]

Probably the Array 3710A is the most cheaper, more of this it's reliable and more serviceable than the others, but I've heard that the software is not so good.

You can try to buy a Chinese Version of the popular Maynuo M971x on aliexpress (the chinese version is the 9710 while the export is the 9711), but Maynuo has explained me that that version is only for the internal chinese market because they "have a high repair rate" and since they are in the same country they can manage the warranty. Buying that model overseas means cheaper price but no warranty.

[ConKbot]

Ive used the 8500 at work and it is a nice piece of equipment, and you certainly could use it to test the peltiers.  IIRC there are chinese OEM versions available for less, perhaps someone else knows more about it.   There are tons of peltiers for pretty cheap on ebay, and of large size too.  You'd definitely want a DC/DC converter to get the maximum amount of power out of the peltiers, and not just heat one side, cool the other and whack it across your battery. You can use the DC load to find your maximum power point, and a cheap thermocouple meter to measure the temperatures of the 2 sides of the pelts, and you should be able to get data which is meaningful.

[Psi]

I know that peltiers produses very little power

If you have enough of a temp difference they can produce a usable amount of power, especially if you have lots of them.



A nice hot wood stove on one side of the peltier and a cold winters day outside on the other should work.
The hard part is getting those two temp extremes close enough together at the peltier without one effecting the other.
Blocks of aluminum spacers inside polystyrene cutouts work ok.

[pilsebob]

Thanks mcinque, ConKbot and Psi for the answers.

The Maynuo M9711 looks very like the BK Precision 8500 (both on the outside and at a glans on the inside but at only half the price). Very interesting product.
The Array 3710A "looks" a bit cheaper on the outside but I will do some exploring on this as well.

Jupp I will need DC-DC converter.
I tried putting the peltier elements in series but it did not work very well.
I hope do do some investigation on that as well when I get a better load.

[mcinque]

The Maynuo M9711 looks very like the BK Precision 8500 (both on the outside and at a glans on the inside but at only half the price).

Consider that both were designed by the same engineer who has founded Maynuo (you can find the same design in the Itech also); keep in mind that the M9711 has 4 data fields at the same time on the lcd, the BK only 2.

If you want to reduce more the price maybe you could take in consideration the BK 8540 (there is also an Itech version) but it's horrible to program by the front panel.

[Phaedrus]

I use an 8514 and two 8540s at work, they're quite reasonable loaders, very reliable. The 8540s are the cheapest BK Precision sells, and if you can do without computer logging they're cheapest way to get a load. Otherwise the 8500 is your best bet.


The Maynuos are the same thing at a lower cost, so if those are available feel free to pick them up instead.

[David Hess]

Why not keep it simple and just use a load resistance and measure the voltage or current?  How complicated does a thermoelectric generator need to be?

[ConKbot]

Why not keep it simple and just use a load resistance and measure the voltage or current?  How complicated does a thermoelectric generator need to be?

Different TEGs will have different maximum power points.  One may like to put out 100mA @ 5V, another may put out 83mA @6v,  giving you the same power from each.  But if you let the first rise to 6v, the current could drop to 75mA.  While you can use a rheostat and a DMM and lots of fiddling by hand. Just whacking a power resistor on the output and measuring the voltage could give you a misleading result.

Doing more than a little power supply work, an electronic load becomes very handy very quickly.   I needed to check some 5v output dc-dc converters at work once. Rather than fiddling with resistors to check the voltage at different loadings, I hook up my e-load, dial it in to constant current, and sweep it from 0% to 110% loading, and monitor the voltage with my DMM over the whole range.  Took about 1 minute per converter to check them out. 

[David Hess]

Why not keep it simple and just use a load resistance and measure the voltage or current?  How complicated does a thermoelectric generator need to be?

Different TEGs will have different maximum power points.  One may like to put out 100mA @ 5V, another may put out 83mA @6v,  giving you the same power from each.  But if you let the first rise to 6v, the current could drop to 75mA.  While you can use a rheostat and a DMM and lots of fiddling by hand. Just whacking a power resistor on the output and measuring the voltage could give you a misleading result.

Doing more than a little power supply work, an electronic load becomes very handy very quickly.   I needed to check some 5v output dc-dc converters at work once. Rather than fiddling with resistors to check the voltage at different loadings, I hook up my e-load, dial it in to constant current, and sweep it from 0% to 110% loading, and monitor the voltage with my DMM over the whole range.  Took about 1 minute per converter to check them out.

I do the same thing when testing regulators over their output range but a standard electronic load is not going to find the maximum power point without automation and that point is going to change at different output powers anyway.  Build one of the simple (analog!) maximum power point converters and attach the output to a resistor.