March 15th, 2009

Peltier demonstration

peltier cooling

For quite a time I was interested about the Peltier coolers, and I ended up buying a small 100W cooling capacity Peltier element. Since you all know, time is always an issue, so this component sit for a year in his box, finally I had the time to try it out.

It’s good to know that standalone Peltier modules do not act as coolers, they just transfer heat from one side to another, from the cool side to the hot side. The simplest way of describing: current is pumped into the Peltier module which translates to pumping heat. Since every current carrying component will generate heat and the Peltier isn’t exception either, beside pumping the heat it will also heat itself.

To achieve the cooling effect it is necessary to dissipate the heat from the hot side, if not the module can reach temperatures above 150-200C and get destroyed. The heat dissipation is made with conventional coolers or forced air coolers.

Now lets talk about numbers, the module I used has 100W cooling capacity when powered from 15V and draws 10A, yes it generates
150W heat to transfer 100W, isn’t very efficient at all since at the end you need to dissipate 250W, which is a lot. Most manufacturers specify also the maximum achievable temperature difference between the cold and hot side, this is usually about 65-79C. So even if you manage to maintain the hot side at 35C, the cool side won’t get below -40C, the good news is that you can stack them up and get larger temperature difference, if you can handle the extra amount of heat generated.

I used a cheap CPU cooler, a small power bench supply for the CPU cooler fan, and a PC ATX supply to power the Peliter.

power supplies
After applying to the Peltier some thermally conductive grease I mounted a copper plate to the cooling end.

parts needed

peltier cooler assembled
Then I powered the cpu cooler fan, and started the ATX power, you can also check on of the previous post about how to turn the ATX supply into bench supply.

atx supply start closeup

And the fun began, since my PC supply is quite weak the voltage dropped to 10V and with 5A the Peltier was working at its 1/3 of capacity, yet it was able to freeze the water drops on the copper plate in a few seconds:
peltier freeze

Important to remember when playing with Peltiers:
1. Always check first which is the cool side or hot side by powering for a short time.
2. Don’t use them without cooler attached.
3. Don’t use thermal grease in excess, it will turn into heat insulator.
4. Always check first the thermal connections.
5. Keep the voltage below the specified maximum.
6. Use sealed type Peltiers, to prevent condensation water short circuits.

You probably wonder if they could be used for heating also, the answer is yes, by reversing the polarity the hot side becomes the cool side and vice-versa, remember always keep the hot side below 150C! And what if you cool one side while heating the other without pumping current into it? You are correct, it will generate current, so the effect is reversible, but the generated current is very small, actually this is the Seabeck effect which is used in thermocouples for temperature measurement.

In overall these Peltiers aren’t effective at all, and draw a great amount of current, but the lack of any moving part makes them ideal when small parts or enclosures need to be cooled.

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Peltier demonstration: [more picture]

Stirling Cooler and Stirling Engine

Stirling Cooler and Stirling Engine

The Stirling cycle machine, which can operate as either an engine or a heat pump, has aroused much interest because of its many favorable characteristics. These include:

  • Minimal pollution. In the case of an engine, the exhaust gases are comparatively clean and cool.
  • Silent and practically vibrationless operation in some configurations.
  • Potential for low fuel or energy consumption. The maximum attainable efficiency or COP for any heat engine operating between the same temperature differential.
  • Multi-fuel capability. The energy source may be almost of any form whatever, so long as it is available at a sufficiently high temperature. Stirling engines have been run on solar energy and a variety of liquid and solid fuels. This applies to heat pumping as well by the use of the duplex configuration.
  • In many instances, it is possible to hermetically seal the machine thus eliminating problems arising from dirt ingress. Some of these configurations have demonstrated operating lives exceeding 10 years.
  • Reversible operation allowing the same device to be used as an environmentally friendly wide temperature range refrigerator or heat pump. This feature also introduces the possibilities of regenerative braking.
  • Reasonable specific power (currently between 0.067 kW(e)/kg for higher power engines down to 0.033 kW(e)/kg for lower power engines). As a low capacity heat pump (up to a few hundred Watts), the specific lift is considerably better than other heat pump technologies (30 to 40 W/kg).
  • Favorable torque characteristics for transportation applications. This leads to simpler transmission designs.
  • Mechanical simplicity. In some configurations gas bearings are easily implemented thus avoiding the need for oil lubrication.

Stirling Cooler and Stirling Engine:


MSI usually not very well known for innovations in the Motherboard area of the market has come up with a design that i think it will sure influence other Motherboard manufacturers in the future. Because the race to more efficient and green electronics has started its just a matter of time until all motherboards will use solutions like this one. Talking about the MSI’s Stirling Engine its simple, the CPU drives its own fan. MSI’s Air Power Cooler uses the energy inherent in the expansion of air as it warms up to drive a fan. As the CPU gets hot, it causes air in a piston to expand. That pushes out the piston rod, which turns the fan rotor, pulling air over a heatpipe-fed heatsink. The heatsing helps cool the piston, so the air inside becomes more dense, pulling the piston rod back to its original position.

MSI’s Stirling Engine-based cooler (powereless) in theory

The mechanism is well known and documented as the Stirling Engine and its named after its creator, Scottish engineer Robert Stirling, who described it in 1816, though the principles on which his machine were based were uncovered in the 17th Century.

MSI’s Stirling Engine-based cooler (powereless) in practice on a motherboard

MSI’s version can transfer over 70 per cent of the heat power to motive power, the company claimed, and it doesn’t use a drop of electricity to drive the fan. It’s not totally efficient, which is why it won’t run in perpetuity, but it is kicked into motion simply by the heat generated by the chip.

MSI has built the powerless cooler and placed it on a motherboard, which it’ll demo at the CeBIT show in Hanover, next week.

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