# How can I tell what amperage a 12V rated electrical device will run at 5V?

I am buying a TEC 12706, a thermoelectric Peltier.

It's rating is: 15.4V 6A (maximum voltage and amperage). I want to run this Peltier at 5V and was wondering how I would convert this data to see what amperage the cooler would draw at 5V.

The only reason I ask this is because before I used ratios to convert (15.4/6 = 12/X) and it didn't work out. For example, I bought a Peltier rated at 6V 2A and it ran at 5V 2.2A and I bought a Peltier rated at 12V 5A that ran at 5V 1.3A. Clearly I am converting somewhere wrong, so any help is appreciated.

• Voltage and current and temperature difference are the variables. You need current AND temperature difference to solve for voltage. – Whit3rd Jan 22 '18 at 9:31
• I'm afraid it gets worse than that. Peltiers are non-ohmic devices. There is a constant voltage source in each peltier, which is determined by the materials that make up the plates. In short...Quantum Physics. – Aron Jan 22 '18 at 10:17
• Possible duplicate of Confusing Peltier Power Draw – winny Jan 22 '18 at 16:00

From the datasheet: The table in the datasheet specifies the module resistance to be 1.9 to 2.3 Ohms. it gives a ball park figure. I say ball park figure because the current cannot be predicted exactly, as it depends on the temperature difference between the plates too.

The graph assumes one has constant current source. In OP case, i assume it is constant voltage source. Still, for a rough estimate, the graph serves good.

The voltage difference generated as the effect of conductor with two different end is termed as Seebeck effect. it is similar to back EMF generated while driving a motor.

This generated voltage is directly proportional to the temperature difference between two ends. Such open circuit voltage is equal to the product of Seebeck coefficient and the temperature difference. Hence, thus higher the temperature difference, more will be the voltage generated. The Seebeck coefficient of metals are mentioned wrt platinum as standard second junction.

This voltage hence tries to reduce the current drawn by the Peltier (Lenz law) when the temperature difference is higher. Since the graph is presented for constant current source, one can see that higher the temperature difference, the voltage needed to maintain the given current is more.

• Umar, you need to account for the constant voltage source of the Seebeck effect. – Aron Jan 22 '18 at 10:22
• This answer completely ignored the Seebeck effect, without which there is no Peltier. – Aron Jan 23 '18 at 2:27
• @aron added info on Seebeck. – User323693 Jan 23 '18 at 7:23