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Forum Index : Electronics : Perfect Toroidal for the OZ Inverter ??

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Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 02:19pm 01 Jan 2017
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Have only just found this thread, there are a few different issues raised here, so I will toss in my two cents worth.

The first question raised was what is the perfect toroid ?
Only half joking when I would have to say free ones !!
As the cost of really large brand new toroidal cores will probably give you a heart attack.

What is the most efficient ?
Now that can have different meanings depending on how you measure efficiency.
Does it mean absolutely minimal zero load standby current ?
Or does it mean best power efficiency running absolutely flat out at full Kilowatts ?
The design approaches to those would need to be be just about exactly opposite.

Deep in my heart I feel there is probably a practical upper power limit to the popular and excellent Oz type of inverter. You can go on adding more mosfets and more or larger toroids, but it starts to get really difficult to get perfect current sharing between the mosfets. And rewinding toroids that are nearly as big as yourself can become a challenge.

Suggestions have been made to split the loads and drive them from individual inverters, or adding grid tie inverters to supplement a main central battery driven inverter. This has the advantage of spreading the risk of losing all power if a single very large inverter has a dramatic failure.
You could reconfigure your loads or plug in a spare standby unit and get things going again pretty quickly.

Briefly mentioned was a mysterious device referred to as a Trace inverter. I have never seen a genuine Trace inverter, but the operating principle is not only interesting, it has some very great advantages of robustness efficiency and reliability. And it really needs no filtering on the output.

Its a very old idea, and not widely known about. Its been around long before the age of mosfets and microprocessors and PWM.
My own home made inverter that is running right now operates on the exact same principle and generates a pure sinewave of many small steps.
Twenty seven steps peak to peak in my inverter, shortly to be replaced with an eighty one step higher powered version.

I did it that way initially just for fun, but it has been so very easy to get going, so trouble free, incredibly robust, and it can be scaled up to any size very easily.
I would not now ever even consider building another PWM inverter, unless it was really small, say 1Kw or less.

Back charging using a main inverter transformer is often used in a UPS where you never need to run both the charger and the inverter together. It can be adapted for grid tie, and is really the same thing. But it does require some pretty sophisticated software and is not worth the complication unless you plan to manufacture, where saving a couple of parts can be important for cost saving.

For home brew, forget back charging. Just build a simple inverter and a separate simple battery charger. Far fewer problems to overcome, and you can upgrade or make changes to either much more easily.
Cheers,  Tony.
 
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