[RFI] Multi-Stage High Efficiency Air Conditioner Units

[K9MA]

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 at sdellington.us