Electronic – Buck-converter dynamic output-voltage using digital-potentiometer

Peltier devices work on current, but usually have significant enough resistance so that voltage control is possible.

Peltier devices are one of the few things you do not want to run with pulses, particularly in cooling applications. The cooling effect is proportional to current, but the internal heating due to \$I^2R\$ losses is proportional to the square of the current. Starting at 0, increasing current causes increasing cooling. However, at some point the resistive heating due to more current outweighs the additional cooling power of the higher current. More current beyond this actually therefore causes less overall cooling. The maximum cooling current is one of the parameters that should be supplied by the manufacturer.

While maximum cooling occurs at some specified current, efficiency steadily decreases with increasing current. Therefore you don't want to PWM a peltier cooler between 0 and the maximum cooling current. Driving it at the steady current to produce the same overall cooling is more efficient.

Of course the microcontroller regulating the temperature will still produce PWM pulses. These pulses need to be filtered so that the Peltier device sees relatively smooth current. The general rule of thumb is to try to keep the ripple below 10% of nominal, but of course that is just a tradeoff someone picked. Fortunately, this is usually not a difficult requirement to design to.

Look at the datasheet, if you can't find it, have a look at the place you bought it from, see if they provide any information about the correct way and voltage to drive the Peltier module.

• The easiest way to check if a larger Peltier module will work better than two smaller ones is to check what wattage each small one is rated for and whether the larger one's wattage (50x50mm is usually 60w) is larger than the sum of the two smaller ones.
• If you have not already, add a heatsink, these things get really hot really fast, and you can damage them if you are not careful, if you add a fan to the heatsink, you will get even colder temperatures on the other side.
• I don't know about the size you have, but you need 12v 60w to power a 50x50mm Peltier module, as I mentioned earlier, double check if the voltage and current ratings are corre4ct for your module.
• If I might offer a suggestion, for prototyping, get a bench power supply, that plugs into the wall, if this is too expensive, you can always an old desktop/laptop power supply with a powerful buck-boost converter. This way, you won't have to waste money on batteries.
• It is also worth mentioning that Peltier modules are not very energy efficient, so unfortunately, you probably won't get the kind of cooling that you are hoping for.