Peltier How-to

Background:

The "Peltier Effect", basically, is the movement of heat to the opposite ends of the joint of two different conductors. It was discovered in 1834 but hasn't been practical until some electrically conductive materials were produced which were poor heat conductors (bismuth telluride). By doping bismuth telluride, the direction of the heat flow can be determined, so it is possible to create a criss-cross pattern of N and P doped bismuth telluride which carry the heat in the same direction even though the direction of the current is changing with the path of the conductor.

A few misconceptions:

  • "Peltiers cool stuff!" Actually, the inverse isn't true either. Peltiers do two things at the same time: 1) move heat from one side to the other, and 2) generates heat. Peltiers generate heat because they are electrically resistive elements. They generate the amount of heat equal to the amount of energy they are consuming (V * A = Watts consumed).
  • "A laptop is a great application for a Peltier!" Maybe if draining your batteries in 30 seconds is OK. Peltiers take a lot of current, so don't use them in applications which don't have an adiquate amount of power available.

    • Applications:

    Applications usually are for those areas which need a temperature differential in a tight space. Large area cooling is *not* a good use. A great application is to accelerate heat transfer from a chip to the heatsink.

    Using a Peltier to Help Cool a Chip:

    The idea of using a Peltier to cool a chip works by putting the Peltier between the chip and heatsink. The Peltier will help move the heat more efficiently from the chip to the heatsink where it can be disapated. This is the proper and safe way to do it:
  • What you need: A peltier of the same area (or slightly larger) than the face of the chip you want to cool, heat-sink compound, and a very flat edge (like a razor blade).
  • Remove the device which contains the chip you want to cool from the PC (mainboard, video card, whatever)
  • Remove the heatsink from the chip carefully, and make sure the face of the chip and heatsink are clean and very flat/smooth
  • Apply a small amount of heat-sink compound using the razor-blade (or other smooth edge) in a uniform and very thin coat onto the heatsink, chip, and Peltier. The idea is to have as little heatsink compound but to also minimize the amount of air. Air is a heat insolator, but heatsink compound is as well, so you want to minimize both. (PS- Don't get heatsink compound in your eye, and wash it off your hands after you use it! It also is messy on clothes and other surfaces, so clean it off any surfaces especially any conductive contacts.)
  • Sandwich together the Peltier being very careful to note which direction it is oriented. Remember one face cools while the other heats! Also make sure that some pressure is being applied to hold the sandwich together, but not too much pressure that the Peltier (which is usually constructed with ceramic faces) might break! If you use screws, be very careful that you don't over-tighten!
  • Test the Peltier by giving it power WHILE THE DEVICE IS UNPOWERED! I.e., power the peltier but not the component being cooled. Note which gets cold and hot. Make sure the heatsink get warm and the chip gets cold. Also power the Peltier only as much as you need. For example, apply 5V to a 12V Peltier for starters. Also be very careful to note how much current the Peltier draws and make sure your power supply can cope!
  • Use lots of fans on the heatsink(s) to dissapate the heat. And don't use the device without power applied to the Peltier! Remember a Peltier is a heat insolator, so without power it TRAPS HEAT! Lastly, check to make sure the chip being cooled doesn't get too cold and start condensing water! Water + electronics = bad If water is condensing, then lower the voltage supply or put a resister in series with the Peltier (of adiquate wattage). On the other side, make sure the heatsink isn't getting too hot to be dangerous.
    • Resources:
  • Melcor -- This is where I got my Peltiers. They probably have the most informative web site regarding the products they sell, but their service was not as curtious (on the phone) or prompt (delivery took several weeks) as it could be.
  • Advanced Thermoelectic Products -- Great info on installing and using Peltiers effectively. Supplier of large and small Peltier modules. I'm not sure if they accept small quantity orders.
  • Teca -- Another Peltier maker. The theory page is interesting, but there isn't much else of use there.

    • Written and copyright (C) by Philip Edelbrock, 1999.