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DC to AC Converter Diagram

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solis365

New Member
What you want is called an inverter. A quick google search for "inverter" schematic yielded several results. I found a VERY VERY basic version of one here:
12Vdc - 120Vac Inverter
The circuit diagram is attached.

This will not produce a sine wave, it will produce a "modified" sine wave, which is going to look more like a square wave. Note on the website it states that you should not run inductive loads (such as motors) from this circuit. It will only do 300W of power with a good enough transformer and heatsinked transistors.

If you want something closer to a sine wave then you will need a more complicated circuit.
 

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audioguru

Well-Known Member
Most Helpful Member
What you want is called an inverter. A quick google search for "inverter" schematic yielded several results. I found a VERY VERY basic version of one here:
12Vdc - 120Vac Inverter
The circuit diagram is attached.
The circuit is a piece of garbage that does not work:
1) Its capacitors are with backwards polarity and explode.
2) Its transistors have avalanche breakdown of their reverse-biased emitter-base junctions that causes extremely high current pulses in the capacitors and explodes them even if their polarity is corrected. Most of the low power from the transistors is wasted.

It will only do 300W of power with a good enough transformer and heatsinked transistors.
No.
The transistors have a very low base current (67mA) so the max output power is about 35W at a low voltage.
If the 2N3055 transistors have 3.3A of base current so that their collector current is 10A each then the output power will be 120W at a low voltage.
The transistors will have 15A which is their max allowed collector current if the base current is 7A but the output power will be only 180W. Where will the 7A of base current come from?
 

phoenox

New Member
Audioguru, you say this circuit is a piece of garbage because of the specific transistor and the capacitor polarity.

Do you think the basic idea of making an inverter using an astable mulivibrator is workable if one was to pick proper transistors (power mosfets?) and wire the caps properly?

Also, does anybody know the purpose of the resistors in series with the flyback diode?
 

audioguru

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NPN silicon transistors have avalanche breakdown when their base is 5V to 7V negative to their emitter. Then the supply for a simple multivibrator should not exceed 5V. In the garbage inverter circuit the base voltage is trying to be almost -23V!
Diodes in series with the bases or emitters will prevent avalanche breakdown.

A square-wave inverter needs an oscillator like a CD4047 that has a perfectly symmetrical dual-polarity output because it has a frequency divider. The oscillator can drive transistors or opamps that are used as Mosfet drivers and then Mosfets drive the transformer.

It is not difficult to convert the square-wave inverter to a modified sine-wave (actually a modified square-wave) inverter. Then voltage regulation and low battery cutoff circuits can be added.

The resistors in series with the diodes absorb the flyback voltage produced by the transformer when it has no load. They waste lots of power.
 

Saad_ak72

New Member
Grid Tie Inverter

Hello everybody. I am new here. I am a final year student of electrical engineering of Electrical and Mechanical Engineering College, NUST Pakistan. I am making a grid tie inverter which will take the energy from solar panels, convert it into electrical energy, and pump it back into our main utility grid thus making our utility meter spin backwards or atleast slow it down. Can you please give me tips on how to go about doing this ?
 

audioguru

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Making an inverter to convert 24VDC to 240VAC at 50Hz and with no current is simple.
But most inverters have a fairly high amount of output current. You forgot to say how much output current or power you need .
You also forgot to say what waveform you want.
 

haroonrashid

New Member
Hi Saad, sorry I am late, just would like to ask you, have you done with the grid tie inverter successfuly?

Hello everybody. I am new here. I am a final year student of electrical engineering of Electrical and Mechanical Engineering College, NUST Pakistan. I am making a grid tie inverter which will take the energy from solar panels, convert it into electrical energy, and pump it back into our main utility grid thus making our utility meter spin backwards or atleast slow it down. Can you please give me tips on how to go about doing this ?
 

audioguru

Well-Known Member
Most Helpful Member
In our part of the world, we must use a circuit that is certified to work properly.
It must be in sync with the grid frequency and it must be able to be turned off by the electrical utility when they do repairs on the transmission lines and transformers.
 
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