Fabrication of semiconductor thermoelectric power generation device

　　Solar photovoltaic power generation requires sunlight and an open sunny space, while wind power generation requires continuous wind and an installation site. Semiconductor temperature difference power generation is not restricted by weather and site, and is increasingly stimulating people's new green desires. The author uses the inlet and outlet water of the honeycomb coal water heater as the temperature difference source to make a semiconductor temperature difference power generation device. The principle block diagram is shown in the figure above.

　　Semiconductor thermoelectric power generation is a solid-state energy conversion method that converts temperature difference energy (heat energy) into electrical energy. The power generation device has no chemical reaction and mechanical movement, no noise, no pollution, no wear, and a long life. Its core component is the semiconductor thermocouple module (because it is mostly used for refrigeration, it is also called semiconductor cooling sheet, which is mostly available in the electronic component market). Connect its two lead wires to the voltage or current block of the multimeter, and conduct body temperature to one side of it to form a temperature difference between the two sides. The pointer will deflect, and the real thermoelectric power generation will be presented in front of you. However, the current thermoelectric conversion efficiency of semiconductor thermocouple modules is low. Studies in recent years have shown that the maximum is less than 5%, which is the biggest obstacle to the practical application of semiconductor thermoelectric power generation.

　　The first thing to do when making a semiconductor thermoelectric power generation device is to choose a temperature difference source. The temperature difference sources available to a family are very limited, but there is a lot to say about them.

　　The first is the cooking temperature difference, burning natural gas, liquefied petroleum gas, coal, biogas, etc. to produce high temperature; the second is the air conditioning and heating temperature difference; the third is the ground temperature difference, the temperature difference between the courtyard well water, stream water and the surface; the fourth is the solar temperature difference, using solar water heaters and solar cookers to obtain heat; the fifth is the temperature difference between ice and snow in winter and indoor and underground, etc. However, the use must meet the requirements of convenient access, economy, sustainability and sufficient energy. Experiments show that for each 1 degree Celsius temperature difference provided by the current common semiconductor temperature difference power generation module, a voltage of about 0.03V can be generated accordingly. It can be seen that there is no practical value if the temperature difference is small. The reason why I chose the inlet and outlet water of the honeycomb coal water heater as the temperature difference source is that the fire is not extinguished day and night, and the temperature difference between the hot water of the stove and the inlet water (tap water) is large, more than 60 degrees Celsius in summer and more than 90 degrees Celsius in winter, and it is relatively stable. At the same time, the pressure of tap water solves the problem of energy lossless transmission. As long as family members use hot water to wash vegetables, dishes, hands, faces, and baths, they can get the ideal temperature difference. It is particularly important to emphasize that the semiconductor thermocouple module is a good heat conductor. If there is no transmission of high and low temperature energy on both sides, the temperature difference cannot be maintained. No matter how good the insulation is, it is useless to make the temperatures on both sides of the module close. This is the root cause of many failure cases. This power generation device uses "passing water", and the energy consumption is considered to be zero. At the same time, the cooling of hot water is not very obvious. The middle picture is a schematic diagram of the structure of the device.

The production points are as follows:

　　1. Production of medium conduit and high and low temperature difference surface.
Thread the two ends of two aluminum tubes with a diameter of 30.5mm and a length of 1000mm so that they can be connected to the cold and hot water pipes of the honeycomb coal water heater through the flexible joint when in use. After processing according to the shape of the cross section in Figure 2, they are welded together with aluminum bars with a width of 60mm, a thickness of 3mm and a length of 1000mm. The welding should be sufficient and thick. The cold and hot end conduction surfaces of the aluminum bar and the semiconductor temperature difference power generation module should be flat and smooth. Then try to arrange the semiconductor temperature difference power generation modules to be installed at intervals between the cold and hot conduction surfaces (the author used a total of 10 pieces), and then drill holes on the edge of the aluminum plate for two fastening bolts on each side of each module. Use an insulating plate to make a groove of suitable size, use an air conditioning insulation sleeve as the insulation material, cut it open and put it on the hot (water) medium conduit, and then fix the insulating plate groove; the cold (water) medium conduit does not need insulation.

　　2. Test, selection and assembly of semiconductor temperature difference power generation modules
Semiconductor temperature difference modules provided by regular manufacturers generally have performance indicators. Don't let the values ​​of more than ten volts and tens of amperes on them make you smile. Those are their power consumption indicators for cooling and heating. They can be very low-energy in power generation. The author has tested the power generation performance of the same batch of products. The no-load voltage is 3.4V and 2.7V, and the no-load current is 1.6A and 0.7A. Only by using those that are particularly sensitive to temperature differences can it be possible to DIY a more ideal power generation device. The specific test method is: use an aluminum heat sink removed from a high-power audio as a cold source (heat dissipation), turn the electric iron to the low temperature gear as a heat source, and use a multimeter to test it. Note that you should pause after testing one piece, let the aluminum heat sink cool down, and then test the next piece, otherwise it will be inaccurate. The next step is to grasp the consistency of the module thickness. Take off the slightly thinner and thicker ones, otherwise the entire component cannot be installed tightly. After completing these tasks, you can proceed with the assembly of the temperature difference power generation module components. Apply a thin layer of thermal grease evenly on both sides of the module, and tighten the four fastening bolts one by one. The module is installed when it is clamped and cannot be moved.

　　3. Connection of power generation module components.
Connect the temperature difference power generation device to the cold and hot water pipelines, and the mechanical assembly is completed. The next step is to detect the power generation working state of the power generation module monomer to see if there is any voltage and current that is obviously low. If most of them are not clamped by the fastening bolts, measures need to be taken to solve them, otherwise they will become loads in parallel and become current "bottleneck" in series. The forward and reverse resistance of the semiconductor temperature difference power generation module is very low. And the difference is not too large, only a few ohms to more than ten ohms when the temperature difference is 10 degrees Celsius. At this time, it is difficult to match the load, and the power generation efficiency is extremely low, but it rises rapidly to the dry ohm level as the temperature difference increases. Due to the installation orientation, the red and black leads do not represent the actual positive and negative. While detecting the working state of the monomer power generation, the positive and negative poles are also clarified. The connection can be made in parallel or series according to the load situation. The total power of the semiconductor power generation module assembly is not equal to the simple addition of the monomer power, but will be much smaller than it, especially in parallel. The author connected all 10 monomer power generation modules in series. When hot water is used at a small flow rate, the open circuit voltage is 13.93V and the open circuit current is 345mA (it is summer, the tap water temperature will drop by 20 to 25 degrees Celsius in winter, and the temperature difference will increase by 15 to 20 degrees Celsius. The power is much greater than in summer): when hot water is stopped, the open circuit voltage is 6.23V and the open circuit current is 7mA.

　　4. Production of control circuit.
This power generation device can directly drive a 9V DC small fan or 50 LED lights in summer, but it can only be synchronized with hot water. If you want to expand the power supply range and use electricity flexibly, you need to configure a control circuit and a battery. The control circuit used by the author is based on the schematic diagram of a charging controller on the "Electronics News". I will not copy it here out of respect for the designer's work. In order to satisfy readers who are interested in this, the author has also made a simple and practical control circuit, see the figure below.

　　The voltage-stabilized charging control circuit is composed of a three-terminal programmable integrated circuit TLA31 and a transistor C2500. This circuit is suitable for a wide range of input voltage changes, and the output voltage is adjustable and has a high stability accuracy. Among them, R2 and R3 are adjustment resistors for the TL431 reference voltage Vref. Changing their resistance values ​​can adjust the output voltage. During debugging, the author took R2=16.81kΩ and R3=12.05kΩ, and the output voltage was stable at 7V, and it could withstand a large change in input voltage from 9V to 20V (or even higher, not measured). The transistor requires a withstand voltage of 30V, a current greater than 0.5A, and hFE120 or above. D1 is an isolation diode, and there is a voltage drop of about 0.5V when connected to the circuit, which should be taken into account when setting the output voltage value. This circuit has a high charging efficiency for 6V lead-acid batteries. When it is close to full, it will switch to trickle charging until the current is zero, and overcharging will not occur. If the output voltage is adjusted to 4.2V, a 3.6V mobile phone battery can be quickly charged. The over-discharge protection of the battery is provided by the inverter (undervoltage alarm), which will not be elaborated here.