Peltier elements or free electricity from a fire

Recommendation points

• Thermoelectric module design
• We collect TEM for 5 V
• Energy furnace

With the help of simple devices, you can use the heat loss from heating air or liquids. In this article, we will show you how to use the waste energy of stoves, boilers and open fires by converting it into a small direct current electric current..

Any chemical process takes place with the release of various kinds of energy. Such a powerful source as combustion has been used at all times. It can be called the primary source of heat and light. Almost all substances on Earth burn, while emitting heat and light in different quantities. Converting thermal energy into electrical energy is not difficult if you have a working steam turbine at hand, similar to those installed at the CHP. This is a bulky and complex device, which is unlikely to find a place in the boiler room of a country house. We will try to benefit from the heat generated by stove heating or water heating.

The Peltier effect is the phenomenon of temperature difference when thermocouples of two different types of conductors (p-type and n-type) interact when a direct current passes through them. The Seebeck effect is a consequence of the Peltier effect, when an electric current is generated when one of the thermocouples is heated. We will not describe in detail the thermodynamics of the process – this information, which is difficult to understand, can be easily found in the reference literature. We are interested in the result and options for its practical use..

Thermoelectric module design

Thermoelectric module (TEM) consists of a plurality of thermocouples interconnected by a copper plate. The thermocouple field is glued between two ceramic plates. It is possible to assemble such a module only in the factory. But it will be possible to assemble several TEMs for your own needs at home. Peltier-Seebeck elements are freely available in specialized stores (and websites) selling technological equipment.

We collect TEM for 5 V

What you need:

• Peltier module TEC1-12705 (40×40) – 2 pcs .;
• step-up converter of constant voltage EK-1674;
• duralumin sheet 3 mm thick;
• water tank with a perfectly flat bottom (bucket);
• hot glue;
• soldering iron.

We cut out two identical plates from a sheet of duralumin, a little more than two modules lying side by side. We fix the plates on the modules on both sides with hot melt glue. We fix (hot melt) the resulting “sandwich” to the bottom of the bucket. Such a design can already be put on fire, but we will get useless 1.5 V at the output. To improve the characteristics, we need a step-up converter, which we solder into the circuit. It will increase the voltage to 5 V, which is already enough to charge a mobile phone..

Attention! The converter has dimensions of 1.5×1.5 cm.In the absence of professional skills, entrust the soldering to a specialist.

The temperature difference in our design is obtained by heating one side (from a furnace or flame) and cooling the other (water in a ladle). Of course, the larger the difference, the more efficient the module will work. Therefore, to operate in the microgenerator mode, a relatively low water temperature in the ladle is required (it is better to replace it periodically). To generate the coveted 5 V, it is enough to put the structure on a glass with a burning candle.

By proportionally combining more modules, we get a more efficient power generation system. Accordingly, increasing the structure, we proportionally increase the heat exchanger. In this case, the surface to be cooled must be completely covered with a container of water (the simplest and most affordable option).

Everything is so simple that immediately there is a desire to assemble more modules into one system and generate 220 V from the fire. And then connect an oil heater or air conditioner. Such a simple system has its drawbacks, and the main one is low efficiency. Usually this figure does not exceed 5%. This leads to a relatively low current strength of 0.5 – 0.8 A and a very low power – up to 4 W.

For a pump or incandescent lamp, this is negligible, but quite sufficient for:

• charging batteries up to motorcycle (in options proportional to the requirements);
• operation of light-emitting diode (LED) lamps;
• radio receiver.

In winter, the system, placed on a heat source located outside, will work as efficiently as possible..

The cost of materials for the assembly of a 5 V thermoelectric microgenerator:

Name	Price, rub.	Note
Peltier module TEC1-12705 (40×40) * – 2 pcs..	600	Price for 2 pcs.
DC voltage boost converter EK-1674	320
Duralumin	300	Sheet for bucket version
Hot melt glue Radial	150	2 ml
Ladle	one hundred	New
Total for materials	1470

* – this item model was selected for price reasons. The range of TEMs from supplier companies is quite wide, which allows you to choose more productive (up to 8 V) models (they are significantly more expensive).

Factory products of this design are just beginning to appear on sale. Serial production is carried out in small batches, and the range is small. The cost of such a “bucket” starts from 2500 rubles.

A factory thermogenerator is a device based on the Peltier-Seebeck effect that can be fixed directly to a heated surface. From the design described above, it is distinguished by the factory design (which means reliability), the absence of a liquid heat exchanger (instead of it – fins for air cooling) and a higher price.

A standard “travel” thermogenerator has the following characteristics:

Voltage	13.5V
Current strength	0.16 A
Power	2.2 watts
Weight	1.6-2 kg
Armored cable	Yes
overheat protection	Yes
Set of standard connectors	Yes
Dimensions (approx)	150x150x200 mm
Price	From 7000 rub.

As you can see from the table, factory reliability and utility are not cheap. However, it cannot be said that it is functionally superior to the homemade version with a bucket. An impressive 13.5 volts will speed up cell phone charging, but you will need to carry 2 kg of weight with you on the hike, which is an unaffordable luxury (given the size of the device). And, of course, the price makes you think. For this amount, you can collect not a “thermal bucket”, but a “thermal pan” and calmly charge your laptop. And one more nuance – the device still requires fixing on a metal plate in case of using an open fire.

In general, this is a pleasant and convenient addition for those who have no problems with money and free space in the trunk..

Energy furnace

To date, an energy furnace is the apotheosis of using TEM in everyday life. This is a factory product, in fact, a stove-stove for any type of solid fuel with an integrated thermoelectric module. Ideal for hunting lodges, summer cottages, remote wintering grounds and in general any kind of life away from civilization. Designed for autonomous use (without peripheral heat sinks), has only a hearth and chimney. Provides food preparation. The most powerful Peltier-Seebeck elements are installed on this furnace..

Energy furnace characteristics:

output power	25-50 W
Output voltage	12 in
Firebox volume	30-60 liters
Weight	30-60 kg
Thermal power	4-6 kW
Stabilizer	Yes
Factory connectors	Yes
overheat protection	Yes
Price	RUB 23,000–40,000.

Although the oven is portable, it is certainly the “heavyweight weight class” among household appliances. However, the range of tasks of the energy furnace is quite wide – it can even charge car batteries, illuminate entire rooms with LED lamps. She will find a place in the expeditionary wagon train and in the hunting all-terrain vehicle, in the technical room and in the country. In other words, in this case, we always have a heat source with us, it remains to find fuel.

In its niche, the energy furnace is irreplaceable, although the service life declared by the manufacturer – 10 years is a little alarming. It should be noted that, as in the thermogenerator, there is the possibility of preventive (or emergency) replacement of all parts up to the body.

Thermoelectric modules are extremely interesting objects. In addition to the methods of application described, they are also used for water and air conditioning. In this case, a direct current is supplied to the same element and it works “in the opposite direction” – it cools the air. This technology is successfully applied in automobile air conditioners and water coolers, in the automotive industry and in the manufacture of microprocessors. We will describe these devices in the next article..