Peltier device... regulating temperature

Further note: the yellow wires are marked "KA" and "KB" on the PCB.

I've drawn out the circuit, KA-KB appears to be the path between -ve and the element when the switch is in the "hot" position, so I guess it's a cutout switch to prevent it getting too warm. The only other components are a couple of LEDs with limiting resistors, and a bridge rectifier to ensure the polarity of the fan is always correct.

Since I'm only interested in cooling I could probably get rid of the PCB and hardwire the fan, peltier device and thermostat... or break the circuit on the cold side of the switch and place the thermostat inline.

That's assuming it's OK to use a thermostat.... :)

The fan in this thing is so noisy that I'm not sure a thermostat is going to be of much use. At 22C ambient the interior of the fridge is about 6 - 7C, which means that even on a reasonably mild day it would be running continously.

The fridge is under my desk, after a couple of hours of sitting at the computer my ears are actually hurting because of the noise......

I presume the fan itself is a vital part of cooling, to keep the temperature on the warm side as low as possible.

um I did a search with google on peltier controller and found this

have a nice day

Also, the peltier device inside the fridge has 4 wires - red&black, plus two yellow. Any ideas what the latter two may be used for, perhaps an internal thermostat?

Thanks in advance...

Peltier fridges are sadly very inefficient and cant really cool all that well. The peltier elements that are usually used are at the best only around

50% efficient and have a maximum temperature differance between the hot and cold side of the element of about 40D max. This means that you have to keep the hot side as close to ambient as you possibly can,and the small fans that usually come with the fridges are too small to do this properly. Its unlikley that if you fit a thermostat, it will ever switch off as the peltier element simply wont be able to pull enuf heat out of the fridge even on a mild day.

The only way Ive found to get any performance out of these fridges is to add more peltoer elements , usually 4 are needed and water cool them using water cooling kits made for cooling CPUs in PCs. Does work, but is expensive, you are much better getting a real portable fridge with a compressor.

Some friends experimented with one and found it would not cool a can of beer to a drinkable temperature.

Friday

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The fridge I have will chill a drink quite nicely (ice also forms near the peltier device), but the fan is so noisy that it hurts my ears. I tried replacing the fan on the back of the case with a smaller a low noise PC case fan bolted "CPU style" to the heatsink and surprisingly it still managed to cool to about 9C with the ambient in the low 20s. The only problem is that there's a fair bit of radiant heat coming from the back which I am not entirely comfortable with.

So it seems that even without moving a shitload of air through the case it can still cool. Some ideas I've come up with...

1) Fixed speed control of the original fan, so that it's still moving enough air to cool the heatsink sufficiently, but not enough to make uncomfortable noise. (Even something basic like feeding it 5V instead of 12V) 2) Temperature based speed control of the original fan... the hotter the heatsink, the faster it turns. 3) Multiple smaller but quieter fans bolted to the heatsink, with one running constantly and the second only switched in when the heatsink gets too warm. Perhaps PWM on the additional fan to reduce the possibility of a rapid temperature change. 4) Digital temperature sensors on the heatsink and inside the fridge with an AVR controlling the speed of the fan(s)

I know that ultimately the fridge itself is quite inefficient, but it was a present and I want to make use of it. :)

Bolt a second to the back of the first. The second will make the first more efficient.