[Elecraft] OT A/C RFI

[Chuck, AE4CW]

Variable speed drives on HVAC units are indeed prone to RFI generation.  Five years ago I ordered a second TRANE HVAC for my home...identical model to the first EXCEPT the VDS was 3/4HP on the first and 1HP on the second.  The first TRANE unit was and is dead quiet...no VSD interference visible on a very sensitive panadapter from 500KHz to 54MHz.  The second unit turned out to be a prodigious RFI producer.  As the installer and TRANE were of no help whatsoever, I contacted the company and engineer who designed the motors (who also happened to be a ham), and here is what I learned:
1) the 3/4HP motor is known to be quiet.
2) the 1HP motor is problematic and RFI is difficult to control.
3) after installing some manufacturer provided filters and personally supplied chokes and capacitors on the 1HP motor, the INSIDE HVAC unit is now quiet. NOTE: Every wire that leaves the enclosure must be filtered.
4) HOWEVER, there was ANOTHER RFI generator in the system.  It turned out to be the cooling fan motor on the OUTSIDE compressor/condenser unit.  This motor was wired to run at a fixed speed and was chosen by TRANE as it is slightly more efficient than the tradition induction motor.

So, yes, choose VSD's for your HVAC system with great caution.  I personally like the variable air flow and increased efficiency, but they can come at a substantial cost in RFI.  While turning the beam around the neighborhood I can easily see multiple VSD dive noise signatures which are usually a burst of very closely spaced carriers (a few hertz apart) spaced about 18KHz apart.
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Chuck, AE4CW

-----Original Message-----
From: Clay Autery [mailto:KY5G at montac.com] 
Sent: Wednesday, July 19, 2017 10:53:AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] OT A/C RFI

Hmmmm....  Jim...  I have a variable speed down-hole pump on my water well...  reckon that could cause RFI via the AC wiring?
The down-hole pump is 220VDC on dedicated circuit, and shack is on a separate dedicated circuit from same service with separate sub-panel.

______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

On 7/18/2017 10:40 PM, Jim Brown wrote:
> On 7/18/2017 6:02 PM, Erik Basilier wrote:
>> Need to replace my A/C, and worried about getting an RFI generator.
>>
>> A few years ago I saw some advice about taming a new unit, and maybe 
>> even getting instructions from the manufacturer.
>
> Dave Cole has given you excellent advice, and you should follow it 
> carefully. I'll add this additional caution. The "upgrade" in HVAC 
> systems (heating, ventilating, air conditioning) is a variable speed 
> motor. The controllers for these motors are notorious for bad RFI, so 
> by all means, do NOT buy that option.
>
> 73, Jim K9YC