Hand tools and fabrication machines
This time I will explain two of the simplest ways to make a 12V to 220V inverter, one with transistors and the other with Mosfet. Most often this type of inverters are made from parts of old PC power supplies.
At the end of the video you can follow the detailed way of making these inverters through many pictures. And now let's focus on the main purpose of this video to test the real capabilities of these devices.
The first test device is made with MJE13007 type transistors. These are NPN Bipolar Power Transistors which are designed for Switching Power Supply Applications.
For the consumer, I used an LED lamp with a power of 8 and 10 watts. We can trace the shape of the output signal before the output rectifier on the oscilloscope. In this case, the DC output voltage is about 240 Volts, and the current is about 8 milliamperes. With a small increase in the power of the consumer, the output voltage drops sharply. These are approximately the limit possibilities of this type of converter.
Next we will test an inverter made with IRF3205 mosfets. The circuit diagram is a bit more complicated, but the features are therefore better.
The DC output voltage is also around 240V and remains above 200V even with a load of 50 to 70 milliamps (10-15 watts). During long-term load, the mosfets remain cool.
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The most difficult part in making the inverters is to find out the correct terminals of the switching transformer. Here are some tips on how to do that. One side of the transformer always has only two active terminals and in our case it is always the secondary winding on which the high voltage is induced. On the primary (other) side there are usually more active leads. There is usually one thicker longer wire which always represents the middle lead. We can determine the other two terminals experimentally, and these are usually either the two middle terminals, or the two terminals at one end.
Based on the previous tests, follows a short conclusion. A common positive feature for both devices is that they use a minimal number of components, are extremely simple to build, require no setup, and almost always work immediately after assembly.
There are more negative sides
- Consumption at idle (no load) in both cases is very high.
- The output signal in these simplest versions is rectangular and high frequency and is not compatible with consumers who are dependent on these components.
- Claims that these inverters can provide 100 watts of power with just two transistors and more than 3000 watts with 12 or more transistors are fantasy.
With a 12V input according to Ohm's Law, in order to get 3000 watts at the output, we need 250 Amperes of current, and all this in case the efficiency of the circuit is 100 percent, which means there are no losses or heating.
The first device with 13007 transistors has almost no use value, except for a simple presentation of how switching devices work. At a load of only a few milliamps, the output voltage drops drastically, so that only a LED lamp of a maximum of 3 Watts can be powered.
The second inverter made with Mosfets is a bit more complicated and generally represents a ZVS driver circuit with several omitted components, since the supply voltage is limited to 12V. At the output, at a voltage greater than 200V, it can deliver a solid 10 watts (about 50 milliamperes) constantly, and in this case the total consumption of the circuit is about 18 watts. After rectifying and filtering the output voltage, this source is quite sufficient to supply the anode voltage for the EL84 Tube Amplifier. After rectifying and filtering the output voltage, this source is quite sufficient to supply the anode voltage for the EL84 Tube Amplifier.
However, if you need such an inverter, it is best to make one with an integrated circuit that is made specifically for this purpose, because in that case the output voltage is stable, often with a sinusoidal shape, and the efficiency is very high.
After all, the price of such inverters (which are very compact by the way) with an output power of about 50 Watts is lower than 5 dollars, so except for educational purposes or for pleasure, it is unprofitable to make such devices ourselves. One such inverter is presented in the picture above