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Re: [RFI] HVAC Variable Speed Motors

To: W2RU - Bud Hippisley <W2RU@frontiernet.net>
Subject: Re: [RFI] HVAC Variable Speed Motors
From: myles landstein <myles.landstein@gmail.com>
Date: Sat, 10 Apr 2010 17:06:03 -0400
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
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

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
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