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[CQ-Contest] Power Inverters

Subject: [CQ-Contest] Power Inverters
From: W8JI@contesting.com (Tom Rauch)
Date: Wed Jan 10 06:18:48 2001
Hi Bob,

 > At 07:11 1/9/01 -0800, Bill Turner, W7TI wrote:
 >  >I am told that to run a computer properly, you need a true sine wave
 >  output >inverter.
 > =======================>
 > If it is determined that a sine wave is needed,
 > but the inverter puts out a square wave......
 > Feed the inverter's output into a transformer, such as a 1:1 isolation
 > type. The output from the transformer will be a sine wave.
 > Square waves fed into a transformer are transformed into sine waves when
 > they exit the opposite winding due to hysterisis effect. Bob

I wish that were true, it would make life easier for all of us.
Unfortunately it isn't.

"Rounding" square waves requires the harmonics be removed, and
that requires the "transformer" have restricted frequency response.
It would require a low-value shunting capacitance, and most
inverters would not like that.

Most don't like reactive loads of any kind.

You can sometimes get away with a series choke, and a shunt
capacitor, followed by another series inductor. This forms a low-
pass filter with a series inductor at the start and end, but then you
run into all sorts of load impedance vs voltage problems! It also
acts like a transmission line or impedance matching system.

It's no simple task to convert a square wave to a sine wave in an
application like this. If it was, you'd see dozens of devices on the
market or else you'd see very few square wave inverters.

73, Tom W8JI

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