[RFI] Multi-Stage High Efficiency Air Conditioner Units

[Kim Elmore]

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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-- 

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)

/"A great second violinist plays second fiddle to no one." //– Robert C. 
Marsh, Chicago Sun-Times./