Thermoelectric Generation

This project explores using a TEG (Thermoelectric Generation) module to create electricity. The module used came with a small fan as it was a replacement kit for a wood stove top fan. Having the fan was useful as small motors can work with less volts than a small light. Using different heat and cold sources will be explored and it is hoped a TEG can be used to power a light while camping.

Fireplace Fan Generator

Aluminum Drink bottle

Heat paste adhesive

Empty beverage can - for the aluminum sheet

Tape

Crocodile clip leads

Digital Infrared Thermometer

A Thermoelectric Generation chip (TEG) chip uses the flow of heat from one of its sides to the other to create electricity. Heating one side can be done by placing the chip on a heat source such as frying pan. The other side needs a heat sink to make it cooler than the hot side. Attaching the TEG chip on the bottom of an aluminum bottle filled with cold water should make for a good heat sink.

1. Heat paste adhesive was used to fix the TEG to the bottom of an aluminum water bottle.
2. An aluminum disk was cut from an empty aluminum can and glued on top of the TEG using heat paste adhesive.
3. The fan which came with the TEG was attached to the bottle using some black tape. How fast it rotates will indicate how much power is being made.

Not all TEGs are created equal: There are different types of TEG chips available for purchase at different prices, many will fail if heated to more than 125c. One of the issues is normal solder used to attach the wires melts at about 180c. So read the specifications of the TEG you are about to buy. The TEG I brought was for use on a wood stove top and so I figured it could withstand higher temperatures. While its specs didn't have a TEG identifier, they said the TEG had as maximum heat resistance of 200c.

Fire:

How hot a small campfire gets was tested by placing an aluminum bar over the flames and measuring its temperature with a thermometer gun. The temperature varied a lot, from 300c to 500c. I concluded it would not make for be a good heat source as it couldn't be easily controlled and could easily cause the TEG to overheat causing the soldered connections to melt and for the TEG to fail.

Kitchen Stove:

A frypan was placed on my kitchen stove and the heat measured using the thermometer gun. I could vary the heat by turning the gas up or down and it was constant. An ideal heat source for testing the TEG module.

Observations:

The aluminum water bottle with attached TEG was filled with cold water and placed on the frypan. When the temperature reached 185c the fan was spinning very fast and moving some air, unfortunately it stopped after only a couple of seconds. My hypothesis being the water in the bottle immediately next to the bottom of the aluminum bottle had heated up and so it was no longer acting as a heat sink which in turn meant there was no longer heat flow within the TEG.

Fresh tap water was put into the bottle and placed on the frying pan. The stove ring was set to its lowest heat setting. It was observed:

1. The fan would just start to spin at 0.3Volts when the pan had reached 60c.
2. An attached garden light LED required 0.7 volts to come on, this was achieved at a temperature of 110c.
3. After about 30 seconds the light went out, after shaking the bottle of water (to mix the water) the light came back on.
4. At a temperature of 120c, the TEG produced 0.9 volts, however the cold side appeared to warm up quite quickly as the TEG stopped working after a few seconds.
5. After 20min of experimenting, the water in the water in the bottle was measured to be 40c.

If the hot side is at 110c and the water in the bottle is 40c, this means the TEG need a 70c temperature difference between hot side and cold side to generate enough to power the garden light LED and fan.

These observations lead to a copy of conclusions:

1. A steady, measurable heat source is required.
2. A constant heat sink is required.

As the TEG works by the temperature difference between its two sides, performance can be improved by making the cold side colder using iced water. A jug of water was placed in the freezer for an hour and a half until it started to freeze, the water was then poured into the aluminum bottle. The base of the bottle was then placed on a frying pan heated to 180c. The fan spun very well and was also able to light a garden light LED (which contains a voltage booster). I measured the power generate at the temperature of 180c, to be over 2 volts, and about 200mA. But it only ran for about 40 seconds before stopping.

Press for a good fit:

I applied some downward pressure on the bottle to make a good connection between it and the TEG. The fan began to spin again. The previously applied heat paste had come away, so pressure was required to ensure a good connection for heat transfer.

The temperature was eased back to 135c. At1 volt both the fan and LED ran well. The fan was removed and the LED shone brighter. The volts also increased. With the fan and LED removed the (non-load) reading was 2 volts. This is a reminder that just taking a volt reading when no work is being done can overestimate the power being generated.

Connecting a Torch:

A small single AAA battery powered torch (with battery removed) was connected to the TEG with some crocodile clips. The light lite up and by keeping the temperature at 125 -135c shone for 35 minutes. The temperature of the water was then measured to be 35c.

Going Colder:

Adding salt to water lowers its freezing point. Meaning it can still be a liquid at a lower temperature. 300gm was mixed with 1-liter of water and placed in the freezer overnight. The -13c water was poured into the aluminum drink bottle and placed on the frying pan. The anticipated increase in voltage didn't occur. Pressure had to be applied to make a good contact between bottle and TEG and keep it working. I found at 125c temp gave 1 volt and ran the LED torch steadily. The water had reached 12c after 14 minutes, 26c after 30 mins and 32c at 40 mins. Even at 0.8volts the LED touch ran steadily but after 40 minute and at 0.7 volts it went out.

The plan now is to use an LED torch with the TEG and fill the bottle with ice water. When camping ice water can be obtained from the bottom of an Esky. A suppressed thought is: 'wouldn't it be better to just fit an AA battery to the torch for light? - Moving right along.

As ice water helped to spin the fan, I tried ice water for the cold and body heat for the hot. Ice water was again poured into the aluminum bottle and the base of the aluminum bottle placed on my leg for heat. The fan started to turn slowly - demonstrating that electricity can be generated using body heat.

As it is the temperature difference between the two sides of the TEG which makes the electricity, I experimented by making the cold side constantly cold by using a block of ice. Ice is a great constant cold source as it won't increase in temperature above 0c.

I placed the base of the bottle on a block of ice for the cold source, for the heat source I filled up the aluminum bottle filled with boiling water. The fan turned. I measured the voltage generated to be about 1.5 volts and Amps at 150mA. The advantage of focusing on the cold source for the heat differential is the TEG won't overheat. 15 minutes past before the fan and garden light stopped.

If 10 of these TEGS were sandwiched between a couple of sheets of aluminum, connected with a voltage booster it seems possible that 5 volts and 300mA could be generated. This might be enough to slowly charge a phone. The heat source could come from a hot water bottle placed on the top of the sandwiched TEGs.

An even colder source would be dry ice as it is much colder than ice made from water. It would be interesting to see if dry ice causes the fan to spin at room temperature.

Hot water and ice worked, so how about hot water, and an ice cold can of beer?

The idea would be to have an empty can filled with hot water sandwiched to a full can of cold beer with the TEG between them. This would heat one side of the TEG and cool the other. I found more research is required to make this work successfully. The main hurdle being the round surface of a full beer can doesn't make good contact with the flat surface of a TEG.

As the TEG had come loose, it was reattached to the base of the water bottle using some recently purchased heat paste adhesive. A newly purchased aluminum heat sink with fins was attached underneath as this would be more robust than the thin aluminum sheet previously used. It would also assist in the uniform heating of the hot side when I small flame was used as a heat source. After applying the thermal paste, a weight was applied on top of the parts to help get a good bond.

The newly attached heat sink was placed on a frying pan and stove but didn't absorb enough heat (as the fins limited contact with the frying pan's surface) to power the attached torch. When a camping stove was tried, the opposite problem resulted, it heated very quickly becoming too hot, resulting in the wires detaching and destroying the TEG.

When I tried to remove the broken TEG from the bottom of the aluminum drink bottle, I found it was securely attached and while trying to pry it off it chipped. It is fair to say when heat paste adhesive is used to attach a heat sink to a TEG expect it to be attached permanently and trying to remove it will likely cause damage.

The non-working TEG was opened up and it was observer there were 126 pairs of connectors.

The fan which came with the TEG was moved to my desk and connected to a 5volt USB power supply. With the higher power it provides excellent air flow and will help to circulate the heat within the room. I had found the power obtained from the TEG wasn't enough for it to spin fast enough to circulate the air. If you have a TEG powered stove top fan, you might find you get better heat circulation by connecting it to a 5-volts USB supply.

Some 'Tea Light' candles had been tried as a heat source for the TEG but didn't give enough heat. Then it occurred to me; 'but they do give good light'. So, for my next camping trip the choice will be between powering an LED torch with a TEG module or using a few Tea Candles for lightening.