SINUS INVERTER PROJECT

[sinus trouble]

Hello Necks!

Whilst this is not directly related to radio as such? I have been experimenting with DIY inverter circuits!

I would not find them to be the most efficient solution in most applications? They could come in handy!

So lets get started!

What is an Inverter? Well it will convert a relatively low DC voltage into high Mains AC voltage! Thats it!

These things are all over the internet ranging from high quality Pro systems to the Nasty unstable junk that will probably end up damaging your equipment!

I decided to go for something which would be simple, stable and have a reasonable waveform!

As this is an ongoing project? I plan to add filtering and protection circuits along the way!

Once i have finalised some component values? I will also design a PCB! But heres what i have so far!

[sinus trouble]

Inverter proto.png

[sinus trouble]

So the circuit above consists of a 4060 IC which is driven by a 3.2768Mhz crystal! (I only had a 3.2Mhz crystal to hand for testing but close enough)

The 4060 then divides the crystal frequency by 16384 to give out 200Hz

This is then fed into a 4013 IC which further divides the 200Hz into two 50Hz pulses!

The following stages will be the Power FETs which i havent completed yet but should work in theory?

The waveform is not great for now! But is rock solid on frequency!

Measurements below!

[sinus trouble]

Inverter Timebase.PNG

[sinus trouble]

As mentioned above! I did not have the correct crystal for the test!

But the frequency held solid @ 48.85Hz which is pretty close to the 50Hz target!

[Albert H]

The problem you'll have is that you're feeding your transformer with square waves. This will cause all sorts of nastiness in the waveform coming out of the high voltage side, and will have a very poor power factor and many appliances don't like squarewave "mains".

You need to synthesise a (more or less) sinewave at the primary side. If you look at the circuit of the old NRG Pro IV stereo coder, have a look at the 19 kHz "sinewave" generator that's around the 4067. With some trivial smoothing after it, that circuit gives a very pure sinewave. You could easily adapt that (or develop something along the same lines) for your inverter.

[sinus trouble]

The problem you'll have is that you're feeding your transformer with square waves. This will cause all sorts of nastiness in the waveform coming out of the high voltage side, and will have a very poor power factor and many appliances don't like squarewave "mains".

I completely agree Albert!

There will be certain appliances that will not be suitable for use with this type of Inverter!

This is also not to be confused with an expensive commercial Inverter which may use "Pulse Width modulation" or other techniques to simulate a sine wave!

The DIY Inverters on the Internet i have witnessed are horribly unstable! Once loaded they go haywire!!

The waveform on my experimental version is rich in harmonics ofcourse! However, The step up transformer (Comming soon) inherently resonates @ 50Hz which should eliminate some of the nastiness!

With additional output filtering? The 50Hz should be a bit cleaner in theory?

I also plan to add feedback to maintain the output voltage to an acceptable level!

[Medley2k]

Nice work Mr Sinus.

[sinus trouble]

You need to synthesise a (more or less) sinewave at the primary side. If you look at the circuit of the old NRG Pro IV stereo coder, have a look at the 19 kHz "sinewave" generator that's around the 4067. With some trivial smoothing after it, that circuit gives a very pure sinewave. You could easily adapt that (or develop something along the same lines) for your inverter.

That is very interesting Albert!

My knowledge of the NRG PRO 4 Stereo Coder is limited to say the least? But defo worth looking into!

Anyways! Im gonna add some power FETs and a transformer to this prototype for now and see what happens?

If the lights flicker and you dont hear from me? Ive gone up in smoke!

[sinus trouble]

Nice work Mr Sinus.

Cheers Geez!

It may look a bit confusing so far? But all will become clear once i add the extra stages!

[sinus trouble]

So i have been doing some more testing and here is what i found!

I mounted the Proto PCB with a pair of FETs onto a metal plate which would create a mechanical structure and also add a bit of heat sinking for the FETs

Picture below!

[sinus trouble]

Inverter Proto 2.png

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Also added a toroidal Transformer to step up the voltage to 230V

Picture below!

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Inverter Transformer.png

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As you can see, The setup is very basic with no protection at all!

I would not recommend attempting anything like this without a controlled environment!!! Heavy currents are present if things go wrong! Not to mention the high voltages involved!

I did run into some problems! The FET gates are very sensitive and are prone to switching on unintentionally!!

After adding a couple of 22K resistors from gate to ground, The FETs were held low until triggered! This eliminated surge currents!

Overall it worked as expected! Idle current was approx 500mA @ 24V

[radium98]

wonderful .....cool

[sinus trouble]

Been a busy week!

Finally got round to working on the Inverter again!

I wanted to put the Inverter under some load and see how it performed? Starting with some simple appliances!

Firstly my soldering irons (15 and 25 Watt) A desktop fan (40 Watt) and finally a Desktop lamp (60 Watt)

All worked great! Frequency stayed on point! Voltage did slump slightly? But i have been a bit conservative with the supply voltage and current during testing!

I added a trailing 13 Amp socket to ease connectivity which also had space for me to integrate an output filter!

Pics below!

[sinus trouble]

Mains Filter.png

[sinus trouble]

The output filter consists of a 50uH inductor (Beside the earth terminal)

And a 330nF Cap in series with a 100 Ohm resistor across the Live and Neutral!

The inductor is not ideal as it needs to be much larger? But is ok for testing!

The filter needs a bit of tweaking? Yet it performs pretty well so far!

[radium98]

nice ....