And again and again and again and again,...........WHERE IS THE FCC? ? ? ?
? ? ! ! !! !! !! !!!
Dave - WØLEV
On Mon, Jul 25, 2022 at 4:40 PM Karin Johnson <karinann@tampabay.rr.com>
wrote:
> Hello Group:
> Given the recent discussion about HVAC systems and RFI, I am writing this
> to
> chime in on an issue that I haven't seen on this reflector. I have had a
> brief discussion with another ham that has the same type of system,
> manufactured by the same vendor. His experience is similar to mine. He
> went a step further than I did and placed many type 31 toroids on the 240
> volt power feeding the compressor, but did not see any decrease in RFI.
> Now to the details.
> About two years ago I had to replace my HVAC system. I wound up having a
> Rheem model RP1748AJVCA unit installed. This system uses a 3 phase motor in
> the outside compressor unit. The 3 phase motor is driven by an inverter
> that is housed in the outside unit enclosure. It is bonded to the
> enclosure
> via its mounting mechanism. The control interface from the thermostat and
> air handler is via RS-485 two wire communication which is routed along with
> the 24VAC power voltage for the outside electronics. Suffice to say this
> is
> an evil system with regard to RFI. The initial installation did not have
> the thermostat/control wiring replaced with shielded type. I had the
> installer come back and replace the wiring with shielded type wiring. This
> helped a bit with the RFI. I also installed type 31 toroids on the control
> wiring at the compressor and also at the air handler. This simple solution
> knocked the RFI down about only 6 dB. Note the RFI is most pronounced from
> about 4 MHz to 18 MHz. The remaining RFI is caused by the inverter running
> the 3 phase compressor. The noise floor increase due to the RFI is about
> 20
> dB, between the compressor being off and the compressor being on.
> Some time ago I believe I had posted a Google Drive link to some
> documentation I developed showing the spectrum analyzer plots taken with
> the
> system off and the system on. I might note that the power feeding the
> compressor inverter control board does have some internal filtering, by
> using toroids of unknown characteristics to me. Along with a substantial
> filter board, which appears to be a common mode filter mounted inside the
> metal enclosure of the outside compressor unit.
>
> My intent of this post is to simply inform folks to be aware of newer HVAC
> systems that use 3 phase inverters to drive the compressor motor.
> I have done a bit of design work to implement a possible solution to the
> RFI
> but its cost is prohibitive at this point in time. I would also have to
> dis-assemble the filtering boards and components on the outside compressor
> unit. Probably voiding the warranty.
>
> So in conclusion, folks, please do your homework and due diligence to
> investigate what type of technology the new HVAC system is going to use.
>
> Regards,
> Karin Anne Johnson P.E. K3UU
> Palm Harbor, Florida
>
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
--
*Dave - WØLEV*
*Just Let Darwin Work*
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|