[RFI] HVAC Variable Speed Motors

Hardy Landskov n7rt at cox.net
Sat Apr 10 16:43:09 PDT 2010

Of course now the natural question is the following:
I am going to be in the market for a new heat pump this Summer. Does anyone 
out there have a make/model number of a heat pump that does not use PWM 
73 Hardy N7RT

----- Original Message ----- 
From: "myles landstein" <myles.landstein at gmail.com>
To: "W2RU - Bud Hippisley" <W2RU at frontiernet.net>
Cc: "Rfi" <RFI at contesting.com>
Sent: Saturday, April 10, 2010 2:06 PM
Subject: Re: [RFI] HVAC Variable Speed Motors

> Aside  from  being    in  agreement
> It's  shocking that it would radiate  as  bad  as  20 acre's  WOW--  you 
> would think  something that  bad   would be   illegal   , isn't it??
> as  an  aside  to my  earlier  email,  forgot to mention those 
> magnatek600 controllers  have  also    wiped out    some  tenants 
> cordless phones  and  am/fm radios
> it's  amazing  such a  wide  band   multi band  interference producing 
> device  can  be allowed   to be sold
> They too had  a  'filter kit '  naturally for sale  thou it should be free 
> (guess this can also be a  small profit  center for them )  which was 
> essentially  a    filter  for the    ac  input, however  no interference 
> was  on the  that  point   ironic
> 73's
> On Apr 10, 2010, at 4:28 PM, W2RU - Bud Hippisley wrote:
>> On Apr 10, 2010, at 4:06 PM, kd4e wrote:
>>> Warning:  Many of the new HVAC systems are promoting
>>> variable-speed motors in their design - it is one way
>>> that they increase the "magic" SEER.
>> The York "Affinity 3S" heat pump system has just such a beast in it. 
>> Wherever you see reference in their literature to a "variable speed air 
>> handler", you know you're dealing with a PWM RFI generator.
>> Recently I had occasion to check the RFI environment around a home with 
>> one of these in it.  The installation was between two and three years old 
>> and had been done by a reputable heating/cooling firm.
>> The RF noise from this system totally wiped out my mobile installation 
>> (TS-480 with a simple Hustler mast / resonator antenna) on at least 80, 
>> 40, and 20, both in the driveway and for at least a quarter mile in each 
>> direction on the road in front of the house.  Similarly, it totally 
>> "trashed" reception on my Radio Shack all-wave portable from the 
>> broadcast band up through 160 meters and beyond, and it was audible no 
>> matter where I carried that receiver on the 20-acre property.  By far the 
>> biggest amplitudes were found at the thermostat on an interior wall of 
>> the main floor and on the power / control wiring at the compressor 
>> outdoors, but there was more than enough hash near _all_ the power wiring 
>> in the house to mess up ham radio reception on any antenna on the 
>> property and for some distance beyond.  Interestingly, the air handler 
>> chassis itself, which was located in an attic area one floor above the 
>> thermostat and not more than 25 feet away, was relatively "quiet".
>> We ran four cycles of turning the system on and off to be absolutely 
>> certain that it was the source of the noise.  As the fan powered down 
>> each time, you could hear the PWM waveform change on my mobile rig, just 
>> before the fan shut off each time.
>> Interestingly, the house had two heat pump systems -- the Affinity 3S, 
>> which handled the heating / cooling for a 2-year-old addition, and 
>> another one, pre-PWM, that handled the original (10-year-old) section of 
>> the house.  We cycled the old heat pump, too, and found it to be 
>> absolutely quiet except for a single RF "click" when it turned on, which 
>> had been my experience in the 1980s when I lived in a heat pump home of 
>> my own.
>> We contacted the dealer that installed the Affinity 3S system, and he 
>> knew nothing about RFI from variable speed motors but he said he would 
>> check with York.  I received a call back the very next morning; York 
>> knows all about the RFI problem and has an RFI Kit for their variable 
>> speed units.  Installed by the local dealer, it would have cost around 
>> $250, plus the cost of 8-conductor shielded wire (!) to run between the 
>> hi-tech thermostat and the air handler chassis in the attic.  Of course, 
>> we don't know how effective any retrofit kit might be, since it's clear 
>> to me (who used to design PWM power circuits for a living) that no 
>> particular effort appears to have been made to isolate the high transient 
>> currents in the motor drive circuitry from other circuitry and leads 
>> going in and out of the chassis, or to keep the PWM current loop area 
>> small.
>> Give York credit for instantly responding with information about their 
>> RFI Kit (which, by the way, is a stock item in their Oklahoma facility), 
>> but wouldn't it be nicer if a little more time and pennies had been put 
>> into minimizing the loop areas and doing some other prudent avoidance 
>> engineering in the first place.  Locking the barn after the horse is out 
>> does not usually lead to a fully satisfactory outcome.
>> Bud, W2RU
>> _______________________________________________
>> RFI mailing list
>> RFI at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi 

More information about the RFI mailing list