[RFI] Rheem AC RFI

Sun Sep 6 11:55:04 EDT 2020

One good example of RFI engineering:

I replaced my rotary 3 phase converter (American Power 20HP) with a 
solid state Phase Perfect.  The PP has 20HP/64a continuous output and a 
10sec surge rating of ~120 amps/phase, needed for starting a 10HP large 
lathe/heavy load spindle, which the AP rotary could not do.

Obviously, I was a bit concerned about RFI from the PP, but since I'm 
either on the radio or in the shop turning off the PP was an alternative.

Well, not necessary.  So far I've not detected any RFI with the PP on 
all the time.  Also, it's audio quiet and has about 80w standby load, so 
I always have 3p on, very convenient, no noise RF or AF (one lathe's 24v 
control transformer buzz is louder).

Grant KZ1W

On 9/5/2020 15:38, Karin Johnson wrote:
> I know that.  I have a lot of experience with these things.
> 
> 50 year career in this type of design.  Lumped constant filters are not
> 
> Missing, just seem to not be that effective in knocking down very LARGE
> 
> Current spikes from high voltage high current inverter. Working outdoors
> 
> In Florida this time of year is no picnic with the heat and humidity.
> 
> I don???t want to drag out the expensive test equipment into the field just
> 
> Yet.
> 
>   
> 
> Tom Mills:
> 
> Yes that could also be an issue.  I had to do that with the old system.
> 
> It used a conventional capacitor start motor for the compressor.  These
> 
> Are sealed units.  The new system uses 3 phase inverter driven compressor
> 
> Motor also sealed unit.  The ECM motor in my old system was pretty quiet
> 
> But being the picky person I am, I decided to add the additional filtering
> 
> Right at the air handler blower motor, and also added shielding for the
> 
> Thermostat connection from the air handler to the thermostat just below
> 
> It in the house.
> 
> The longer run out to the compressor used un-shielded wiring and I put
> 
> A type 31 toroid there just as a safety measure.  Overkill is wonderful.
> 
> No noise with the old system.
> 
>   
> 
> Now with the new so called ???state of the art??? system the noise sources
> 
> Are much different.  Eventually I will get this solved.  Just takes a bit
> 
> Of time.  Especially since I know where the source is.
> 
>   
> 
> Karin Anne Johnson  P.E.  K3UU
> 
> Palm Harbor, FL
> 
>   
> 
>    _____
> 
> From: David Eckhardt [mailto:davearea51a at gmail.com]
> Sent: Saturday, September 05, 2020 3:57 PM
> To: Karin Johnson
> Cc: Rfi List
> Subject: Re: [RFI] Rheem AC RFI
> 
>   
> 
> You don't look at the 6.5 kHz, specifically!  Look for the noise on
> 40-meters or wherever the problem is occurring.  Once you find that noise,
> look for tyne spacing of 6.5 kHz which should be characteristic of the
> advertised switching frequency.  This is typical of switchers.  From
> experience as an EMC/RFI engineer, when a common mode choke is left out of
> the AC line input (a common practice from China and other CM's), I usually
> see a large hump of broadband noise between 40 and 70 MHz.  Looking at that
> closer, I usually am able to pick out the switching frequency by observing
> the tyne spacing.  Do the same for your interference.  First find the
> broadband noise at the same frequency you are receiving it on the spectrum
> analyzer.  Then look closer-in where the noise is strongest to observe the
> tyne spacing.  You will likely need narrower RBW and span to view the tynes
> once you find the noise at frequency.
> 
>   
> 
> Dave - W??LEV
> 
>   
> 
> On Sat, Sep 5, 2020 at 6:41 PM Karin Johnson <karinann at tampabay.rr.com>
> wrote:
> 
> David:
> 
> Thank you for the reply.
> 
> My spectrum analyzer is a Tektronix 7L12.  Although the lower
> 
> Frequency limit is DC, it is difficult to resolve meaningful signals
> 
> At very low frequencies due to the Zero marker leak thru masking
> 
> Any signals.
> 
> I will say that at HF frequencies above 3 MHz below 8 MHz is where most
> 
> Of the RFI is showing up.  Using the spectrum analyzer in  zero span mode
> 
> There is a very complex switching waveform which is hard to separate out
> 
> any 6500 Hz components.  Viewing the spectrum it occupies the above
> frequency
> 
> range.  Below about 3 MHz there is very little energy showing.  The AM
> broadcast
> 
> Band is not affected at all.
> 
> Using some basic DF techniques I am pretty sure that the source is the
> inverter
> 
> driving the compressor motor.
> 
> Just to clarify.  The COMPRESSOR motor is a three phase motor as shown in
> the
> 
> Rheem documentation.  It is not self contained ECM motor, nor is it a
> capacitor
> 
> Start type motor.  It is truly a three phase motor.  I have not had the
> external
> 
> Metal surrounding all of the outside electronics off just yet, as I don't
> want to
> 
> Go too far down the rabbit hole with regard to voiding any warranty.
> 
> I thought posting to this list might show another user with similar issues
> with a
> 
> similar unit.  I suspect there will be several solutions applied in the
> final accounting
> 
> to solve this issue.
> 
> Right now the installers used the original un-shielded control wiring from
> the inside
> 
> Thermostat to the outside electronics.  One part of the solution may be
> having to
> 
> Replace the un-shielded control wiring with shielded control wiring.
> 
> This system is sort of a state of the art control system, as it uses what
> Rheem calls
> 
> ECONET.  The thermostat does not send a solid control signal generated by a
> closed
> 
> Or open relay in the thermostat.  It uses a binary data stream coming from
> the Thermostat
> 
> to the outside compressor unit and also the Air handler in the attic.  Sort
> of like a CAN bus
> 
> communication system.  I'm not sure what the protocol and physical layer
> component are.
> 
> 
> 
> I am speculating at this point, but this may be as simple as re-routing some
> of the internal
> 
> Wiring in the outside unit to prevent coupling of the high power switching
> components from
> 
> being coupled on to low voltage wiring.  One cannot simply put a low pass
> filter on the data
> 
> Lines coming from the thermostat as it would kill the waveform logic high
> and low.
> 
> Common mode choke would be good here.   When they installed the new unit
> they
> 
> Took off a common mode choke I had installed on the old thermostat control
> wiring at the
> 
> outside unit.  The installers did not leave enough slack in the control
> cable to install another
> 
> Choke.
> 
> Plus one other horrible thought.  If the high voltage inverter switching
> signals are coupling to
> 
> The actual high side and low side Freon copper piping that presents a
> difficult problem to solve.
> 
> Right now I'm just familiarizing myself with the system components.  So that
> I can drag
> 
> The scope and current probes outside and do some more measurements.
> 
> 
> 
> Karin Anne Johnson  P.E. K3UU
> 
> Palm Harbor, FL
> 
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
> 
> 
> 