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Re: [RFI] Sine wave correction for small generators

To: "Kenneth G. Gordon" <kgordon2006@frontier.com>, RFI@contesting.com
Subject: Re: [RFI] Sine wave correction for small generators
From: Grant Saviers <grants2@pacbell.net>
Date: Sat, 31 Oct 2020 21:01:27 -0700
List-post: <mailto:rfi@contesting.com>
Is your gen an inverter type? At 7.5kw a bit unusual for a residence. Then the inverter types use a multi KHz inverter frequency and produce a reasonable sine wave (some near perfect). OTOH, cheap DC to AC "modified sine wave" inverters do have the stepped wave you have heard about. "Pure sine wave" use a multi KHz frequency so more closely approximate sine. Both can have bad RFI.

You might have a standard AC generator, which can have a high distortion output when they skimped on the iron & copper. I've seen awful. It might have a spec. Worth a look on a scope.

Making a standard isolation transformer a tuned circuit may be possible, but it might create a large circulating current. The classic passive regulating technology is a ferroresonant transformer. The primary magnetic circuit is modulated by a secondary resonant winding and capacitor.

There are alternative designs depending on the goals for the output. We used 100% passive ferroresonant power supplies for many years at DEC for transistor logic computer DC supplies, about +/-10% line+load regulation which was designed into the R, S, K & B logic families. When TTL came along then active regulated supplies were necessary. For an industrial/lab/realtime computer, ferroresonant was a great technology for noise isolation, increased line dropout resistance, and great reliability.

The Sola "Constavolt" is a classic passive AC line regulator, available on ebay to a several hundred VA capacity.

see also https://www.generaltransformer.com/ferroresonant-transformers

Grant KZ1W

On 10/31/2020 20:06, Kenneth G. Gordon wrote:
I am considering adding a 60 Hz "tuned circuit" in line after my emergency 7500 
watt
generator. Although I have not yet looked at the wave-form of the output, from 
what I read, it
is essentially a "stepped" representation of a sine wave, which is, in my 
opinion, very dirty.

I have two, very heavy, 115-to-115 VAC, 15 amp transformers (they weigh at 
least 50 lbs
each).

I am considering paralleling enough capacitors on the inputs and outputs of the 
two
transformers to result in 60 Hz tuned circuits in an attempt to smooth out the 
"stepped" 60 Hz
waveform.

Has anyone tried this and if so what was your result?

Ken W7EKB
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