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Recently I ordered a Peltier unit online and received it yesterday. Naturally, I was very excited to play with it. When I first turned it on, One side got hot, an another very cold. I had read that I should attach a heat sink to the hot side of the unit. So straight away, I attached a heat sink and a fan to the hot side (The fan is pulling air out).

I also added a heat sink to the cool side. However, both sides started getting very hot. I have tried reversing the polarity, changing the fan to push, and used voltages from 4 to 12. After nothing worked, I removed the heat sink on the cold side, But still, both side remain stubborn and insist on getting painstakingly hot.

Anyone got Any Ideas as to what's wrong?

Also, If it helps, at 12v the unit is using roughly 2A...

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    \$\begingroup\$ It might help if you post the part number or spec of the part you have - I suspect you've damaged it by exceeding its rating or using it incorrectly. \$\endgroup\$
    – John U
    Commented Nov 15, 2013 at 12:05
  • \$\begingroup\$ Does the peltier element still work when it is used alone? \$\endgroup\$
    – posipiet
    Commented Nov 15, 2013 at 13:01
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    \$\begingroup\$ So what exactly is the problem? What you've described is exactly what a Peltier plate does. \$\endgroup\$
    – Matt Young
    Commented Nov 15, 2013 at 13:35
  • \$\begingroup\$ Hot side heatsink efficient enough to pull the heat away? \$\endgroup\$
    – dext0rb
    Commented Nov 15, 2013 at 17:34
  • \$\begingroup\$ I'm pretty sure if you overheat a peltier device, it just turns into a heater (the PN junctions diffuse too much, and stop being PN junctions). If you let it get too hot, it might have damaged it. \$\endgroup\$
    – Connor Wolf
    Commented Feb 20, 2017 at 22:46

4 Answers 4

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A peltier element is, in this order:

1.) a heater

2.) a thermal shortcut

3.) a thermal transfer unit

What happens is this: When you turn it on, the whole unit starts to heat up. But one side is somewhat cooler than the other. At first, one side feels warm, one side feels cold. Then the whole unit becomes hot because it is a heater primarily. The small difference of maybe 10 degrees between sides is not noticeable when one is 60C and the other is 70C. Source: [1]: http://quick-cool.de/peltierelemente/fragen-zu-peltierelementen.htm "FAQ Peltier German"

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    \$\begingroup\$ Thanks! So, Does that just mean that I need a much stronger heat sink/fan for the hot side? Also, Should I bother putting a heat sink on the colder side, or just leave it be? \$\endgroup\$
    – Sasha
    Commented Nov 15, 2013 at 23:12
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    \$\begingroup\$ Yes, you need an appropriate big cooler on the hot side, as bit as possible and sensible. Depending on what you are cooling, you may or may not need a fan on the cold side. \$\endgroup\$
    – posipiet
    Commented Nov 18, 2013 at 10:47
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A peltier junction creates a differential in temperature. Within certain limits cool side will be 10°C - 20°C lower than the hot side. It's a relative cold, not an absolute one. Discard your anthropomorphic definition of cold and hot.

So, calculate accordingly, if you keep the hot side appropriately cooled then the cool side will be whatever your differential is below that. If the hot side is boiling hot the cool side is going to be near boiling hot too.

Use thermal paste along with your heatsink for better results.

Don't expect magic, you're still increasing the entropy in the universe. You're not going to get free cold.

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  • \$\begingroup\$ "Free cold" made me chuckle :) \$\endgroup\$
    – EasyOhm
    Commented Oct 1, 2018 at 3:24
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You are not getting the "proper" hot side cold enough. Most units are on the order of 12v @ 6A which is 72W, emitting a huge boatload of heat. Put a massive heatsink on it (repurpose one from an old CPU) and submerge the fins in a bowl of ice water. If this doesn't make your cold side frosty cold, you have ruined the Peltier unit.

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There are three things that can get the cold side of a Peltier Plate hot: 1- The most likely cause is the wrong current feed. Check the manufacturer's specifications for the correct voltage-amperes. When the power is just too high, both sides will warm up. You can even burn it. It's not just voltage. Amperes are also critical on this. 2- Heat transfer. If you are using metal pieces to hold the heat-sinks together, they could be transferring heat from the hot to the cold side. 3- Hot side not ventilated enough. This is the most unlikely, but still possible. You may want to tunnel the air-flow trough the heat-sink.

I hope this helps.

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