Minimum voltage input for thermoelectric unit

Question

Context: I am trying to make a drink cooler with a thermoelectric unit (peltier unit). I want to supply the minimum amount of energy as possible to the peltier unit. Now on my peltier unit, it says "15V" (and 68W). I am not sure whether it is recommended, minimum or maximum.

I would have probably just tried to find a batter that can provide 15V but there were two discoveries that I made which suggest I could possibly get away with providing less voltage power supply.

1. I read somewhere that peltier units in general can handle between 3 and 15 volts.
2. I bought a drink cooler using a peltier unit and it is charged by a USB (5V).

Questions:

1. Are peltier units capable of taking varying amounts of voltage without hindering its quality or damage it?
2. If so, how would I go about finding what it needs as a minimum voltage input?
3. Does all my above questions not matter because if I lower my voltage, the peltier will draw more current to meet the power rating (68W)?
4. Does the power rating of 68W mean, "I need that power as a minimum all the time!"

Answer 1

Without a datasheet, I'd assume that 15 volts is the maximum voltage that should be used, and that, at that voltage, the device will draw 68 watts. If you supply a lower voltage, the Peltier device willl draw less current and less than 68 watts.

Answer 2

15V is the maximum, so is 68W. In general the peltier gets more efficient with lower voltage/current, and between 8 and 11 volts is the sweet spot. You of course get less total cooling at lower power inputs, but the efficiency of heat transfer goes up and you have less heat to dissipate. I could not find the graph that relates these, but it is complex since the voltage, current, watts, total cooling, total heat output, Th and Tc and efficiency are all related. As an aside, make sure you deliver smooth power as peltier does not like ripple or being controlled by PWM.