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
circuitry?
73 Hardy N7RT
----- Original Message -----
From: "myles landstein" <myles.landstein@gmail.com>
To: "W2RU - Bud Hippisley" <W2RU@frontiernet.net>
Cc: "Rfi" <RFI@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
>>
>>
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