[RFI] Multi-Stage High Efficiency Air Conditioner Units

[Grant Saviers]

I have a Carrier heat pump, but it is two speed, not variable speed. 
The HVAC engineer (who is the best I've ever met) said, "in our climate 
it's not worth the extra complexity & cost for the small EER 
improvement."  No RFI for me.

Grant KZ1W
Redmond, WA

PS Kwh are cheap here.

On 2/17/2020 19:10, 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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