[RFI] Sine wave correction for small generators
grants2 at pacbell.net
Sun Nov 1 00:01:27 EDT 2020
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
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
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
> 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
> Has anyone tried this and if so what was your result?
> Ken W7EKB
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> RFI at contesting.com
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