For quite a time I was interested about the Peltier coolers, and I ended up buying a small 100W cooling capacity Peltier element. Since you all know, time is always an issue, so this component sit for a year in his box, finally I had the time to try it out.
It’s good to know that standalone Peltier modules do not act as coolers, they just transfer heat from one side to another, from the cool side to the hot side. The simplest way of describing: current is pumped into the Peltier module which translates to pumping heat. Since every current carrying component will generate heat and the Peltier isn’t exception either, beside pumping the heat it will also heat itself.
To achieve the cooling effect it is necessary to dissipate the heat from the hot side, if not the module can reach temperatures above 150-200C and get destroyed. The heat dissipation is made with conventional coolers or forced air coolers.
Now lets talk about numbers, the module I used has 100W cooling capacity when powered from 15V and draws 10A, yes it generates
150W heat to transfer 100W, isn’t very efficient at all since at the end you need to dissipate 250W, which is a lot. Most manufacturers specify also the maximum achievable temperature difference between the cold and hot side, this is usually about 65-79C. So even if you manage to maintain the hot side at 35C, the cool side won’t get below -40C, the good news is that you can stack them up and get larger temperature difference, if you can handle the extra amount of heat generated.
I used a cheap CPU cooler, a small power bench supply for the CPU cooler fan, and a PC ATX supply to power the Peliter.
Then I powered the cpu cooler fan, and started the ATX power, you can also check on of the previous post about how to turn the ATX supply into bench supply.
And the fun began, since my PC supply is quite weak the voltage dropped to 10V and with 5A the Peltier was working at its 1/3 of capacity, yet it was able to freeze the water drops on the copper plate in a few seconds:
Important to remember when playing with Peltiers:
1. Always check first which is the cool side or hot side by powering for a short time.
2. Don’t use them without cooler attached.
3. Don’t use thermal grease in excess, it will turn into heat insulator.
4. Always check first the thermal connections.
5. Keep the voltage below the specified maximum.
6. Use sealed type Peltiers, to prevent condensation water short circuits.
You probably wonder if they could be used for heating also, the answer is yes, by reversing the polarity the hot side becomes the cool side and vice-versa, remember always keep the hot side below 150C! And what if you cool one side while heating the other without pumping current into it? You are correct, it will generate current, so the effect is reversible, but the generated current is very small, actually this is the Seabeck effect which is used in thermocouples for temperature measurement.
In overall these Peltiers aren’t effective at all, and draw a great amount of current, but the lack of any moving part makes them ideal when small parts or enclosures need to be cooled.
Peltier demonstration: [more picture]