# Peltier Module/TEG specs explainantion

I am looking for a Peltier module/TEG to power wearables and I'm not quite sure what specs I need or should be looking at. To be honest I am not quite sure what some of the specs even me. Essentially body heat should be used to power the device.I am most interested in what the following specs mean:

Qmax @ Th
Delta Tmax @ Th

Also, the operating temperature in the specs, does it refer to the temperature that the device will perform optimally, or does it refer to the temperature that is required for the device to operate?

QMax is the max amount of power it can pump at a specific average temperature across the device.

Delta T Max is the difference in temperature it will generate/need at the QMax condition.

However those numbers are just marketing numbers so you can compare unit to unit. The device can actually operate over a wide range on temperatures but the efficiency changes with average temperature.

It's complicated. You need to look at the charts on the data sheet.

• So what would be some ideal specs if I'm looking to power something using body heat?
– ALUW
May 6, 2017 at 17:09
• @ALUW they seldom give you the electrical generation specs. You would need to get some and see. But with only around 10C TD from body to air, you wont get much out of one. In the middle of winter with -40C on the outside you would get more, but the wearer would not be too comfortable. May 6, 2017 at 17:14

Unless you have quite extraordinarily low power requirements, you can forget body power. Let us reason together.

The surface area of the average human is in the range of about 1.5 to 2 square meters. Let's go with 1.5. Resting metabolism is about 100 watts, although a lot of this is lost to exhalation. Now let's assume that you have a TEG with dimensions of 50 x 50 mm, for an area of .0025 square meters. Then the power available for each TEG is (roughly) .0025 x 100 / 1.5, or something like .167 watts. And that assumes that the outside surface is at absolute zero. Now assume 10% efficiency in the TEG (a very optimistic number) and you have an upper limit of about 17 mW per TEG.

Is that a reasonable starting point? Not hardly. See here for experimental data. With a 20 C temperature differential, which seems like a pretty good maximum for other than Arctic environments, efficiencies of less than 1% are recorded. So 1.5 mW seems a much more reasonable SWAG (Scientific Wild-Ass Guess). This is, of course, per TEG, so if you want to walk around looking like an armadillo you might get up to the 100 mW range.