OFF THE GRID

When I lived on the farm; beyond normal household appliances I had a wood burning stove for cooking and heating, a PTO powered generator for when there was no wind, and a windmill for hydro and water when there was wind, but not much in solar power. Most of the time I lived on the grid, but when the power was out for weeks during the ice storm that hit Ontario and Quebec or the blackout that hit the whole east coast, other than a couple added chores my life did not change we even had a windmill in the field to water the cattle.

I grow crops and raised livestock as well as I am a good hunter, gatherer, and fisherman, I can get my meals from the wilderness when I need too.

I live in town now the bylaws don’t allow me to install a windmill or a wood burning stove so I have a propane barbeque with extra tanks for cooking when the hydro is out. $200.oo

I have a Coalman 3750 portable generator and two jerry cans of gas to run the refrigerator and freezer in the summer and the furnace in the winter. In the winter I can put the refrigerator and freezer outside in the cold. I could not build one for the $175.oo this one cost me. For the generator fuel, additive will make the gas last a year in storage.

I have flashlights that don’t need batteries the little one you pump to charge up, the larger one you shake to charge up. 12 of them at $2.oo each I can’t build them that cheaply.

This 400 watt power inverter is strong enough to run my satellite and TV, it cost me $25.oo easier and cheaper to buy than to build. A friend of mine got a 1000 watt inverter for $10.oo.

Other than the solar array I built the other 12 volt 2 watt cost me $20.oo for the pair. I use these to charge batteries.

Other than solar arrays I build power packs, this portable power pack I built from components I retrieved from the garbage it consists of a 12 volt 10 watt hour deep charge battery and a 200 watt inverter all of which I got from the garbage. This power pack combined with my laptop can keep me connected to the internet all evening while it charges and runs off my solar cells during the day.

Due to a lightning strike I lost a lot of work that was not on the net, the lightning strike fried my computer and the backup connected to it. So I have been redoing a lot of my work now I regularly copy my work on CD disks.

I was inspired to design this modified sine wave generator by thirteen, two thousand watt, industrial power inverter circuit boards; I bought for ten dollars. I took one circuit board apart to reverse engineer how it worked, and it did not have a signal generator. They are four-bank push pull mosfet driven inverters, beyond the difficulty of building a four bank sine wave driver I know the optocouplers on the circuit board cannot handle a sign wave driver, so I designed a modified sine wave signal generator.

Pure sine wave inverters are best, however they are expensive to buy or build. Modified sine wave inverters will power some equipment square wave inverters will not, and cost about the same as square wave inverters to build or buy.

This final circuit just needs a couple tweaks on the battery monitor and fan control circuits.

I should be able to build a 120 240 volt 22,000 watt power supply to power my home with circuits left over.

I am already building a circuit board for the modified sine wave signal so I don’t want to modify the Inverter boards. Finding connecting leads has been a pain. These I salvaged from old computers.

There is a lot you need to know to completely design an inverter this is just the basics to help you build your own.

Unless you can acquire a custom made transformer your circuit design is ruled by the transformer available to you, if the primary winding is not center taped you are limited to an AB driver. The only transformer you can play with is a center tap primary, if the primary winding is center taped then you can use an A, B, C, and AB inverter driver and it can be supplied with 12 or 24 volts and 6 or 12 volts you can’t play with the watts.

If the primary winding is 1000 watts run max then your inverter is limited to 1000 watts run max and about 1500 watts startup surges.

The transistors and mosfets should be watts doubled, take an IRF640 it is 200 volts 16 amps and 136 watts. That is 200 volts at 0.68 amps to 8.5 volts at 16 amps not 200 volts at 16 amps. An IRF640 will get hot at 12 volts 11 amps constant running doubling the transistors and mosfets will keep them from overheating at full wattage use.

Optoisolators protect the signal circuit from feedback and power surges; they send the signal from the signal generator by light in one direction to the transistor bank.

These three 50 Hz inverter circuit designs are easy to build and the signal circuit is accurate to 1%.

This circuit can be broken down to seven components.

1. Power Supply
2. Voltage Regulator
3. Timer
4. Signal Converter
5. Optoisolation
6. Inverter Transistor Bank
7. Transformer
There can be more components when you add charging and low battery circuits.

These circuits are 24 volts center grounded and AB type inverter; 12 volts center taped primary winding B type inverter, and 12 volt AB type inverter.

Voltage regulator components
1-LM7805
3-1N4002 diodes
1-220uF 16v
1-1uF 16v
1-1uF 6v
1-LED
1-1 k&

Timer Components
1-NE555
1-12 k&
Use 1-24 k& for 60 CY or 1-30 k& for 50 CY or 1-39 k& for 40 CY
1-0.1 uF
1-10 nF
Any multivibrator with a 240 Hz output for 60 cycles, 200 Hz for 50 cycle, and 160 Hz for 40 cycles will due for the timer circuit. The duty cycle is not important as the first JK flip flop converts the signal to 50% duty cycle and ½ the hurts’.

Signal Converter Components
1-SN74LS73
1-SN74LS08
2 to 4-1.5 k&

From the And gate output resistors to the rest of the Inverter circuit the value of the active components depends on the power supply and the inverter transformer.

If you have a digital analyser the internal signals should look like this, however if you don’t have a digital analyser slowing down the frequency and using LEDs can enable you to see the signals.

I hope this will help others build Inverters.