Just about every modern appliance with motors uses a variable speed
drive of this sort. Washers, refrigerators, furnaces, etc. It's
basically a switching supply. It can be made RFI quiet, if it's designed
and built right.
73,
Scott K9MA
On 2/17/2020 21:10, Kim Elmore wrote:
It seems that I may have used the wrong terminology, as the latest
approach to this is "variable speed compressor," where the compressor
speed is varied. Looking briefly into this, I found that some
companies tout that they do this with an inverter. apparently, AC
input is rectified, possibly filtered, then converted to variable
frequency AC, which is used to control the compressor speed. Depending
on how that's done, it sounds like it could either be RFI-silent, or a
catastrophic screamer.
I have a bid on a Carrier system -- does anyone have experience with
variable-speed Carrier units? Does anyone have contacts at Carrier
that I could talk to about any RFI associated the units that have been
specified in the bid and what measures might need to be taken?
Kim N5OP
On 2/9/2020 7:09 AM, Paul Christensen wrote:
"I put a pair of small pie wound chokes in series with the + and return
lines at the box's keying jack and that fixed the problem."
That often works fine on control circuits but for audio circuits and
other
circuits that require maintaining signal waveform integrity, I now use
common-mode chokes and abandoned differential-mode filtering that uses
Pi-section L and bypass C components. For example, pass a square
wave, or
any other fast, complex waveform through a Pi-section choke and
observe the
result. Even when properly terminated, large overshoot spikes and
ringing
results.
By contrast, a CM choke does not affect differential mode signaling as
there's no differential series L due to inductance cancellation. A
CM choke
yields 2*L on common-mode currents, or twice the inductance of a single
winding.
We also need to be mindful of series resistance when using simple series
chokes in power supplies and high-power audio output circuits. We can
mostly ignore that with CM chokes except for the added wiring resistance
required with each turn through a core.
Paul, W9AC
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Scott K9MA
k9ma@sdellington.us
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