[R-390] High Electrical hash noise level

Tue Mar 29 12:16:20 EDT 2011

Curt
I did a little scanning on the net for info on Pulse Width Modulation  and you are probably correct about the use of a PWM drive.  I still haven't heard from Trane or the Dealer but from my very limited knowledge of PWM and what I found on the net, it appears what Trane is using is a Direct Torque Control PWM controller on their fan inducer motor.  From what I read, this type of PWM is directly related to Delta PWM that generates a full spectrum noise (no particular harmonics) sawtooth wave shaped into an AC voltage sine wave format within certain limits and is used to drive AC motors.  This would explain the hash all over the spectrum.

Also, you can actually hear the pitch of the noise change (which I would think would be the changing of the sine wave format) as, from what I would guess, is the controller calculating the changes for the characteristics of the motor voltage to match the fan's load prior to the main furnace blower turning on. 

You know, this is actually kind of like an ignition noise problem from the days when we had contact point ignition systems that generated interference in our car AM radios.  A viable solution to this might be in my 1964 ARRL Radio handbook!  If I remember correctly it was basically 1.) bypass every wire in sight, 2.) shield every wire in sight, and 3.) thoroughly ground the shields.

Which, when you think about the age of the R390A is sort of actually appropriate in an ironic sort of way....

And, of course, the simplest solution is just turn off the furnace when I have my radio equipment on the air!  ; - )

-- Steve, K7PZN 
"Think Quickly, Speak Slowly, Work Diligently, Live Simply"

--- On Tue, 3/29/11, Curt Nixon <cptcurt at flash.net> wrote:

From: Curt Nixon <cptcurt at flash.net>
Subject: Re: [R-390] High Electrical hash noise level
To: 
Cc: r-390 at mailman.qth.net
Date: Tuesday, March 29, 2011, 6:31 AM

What the heck kind of motor for a blower does that?

I haven't seen alot, but the ones I have seen are small 1/30HP reactance 
limited, induction motors that run at 3000 RPM direct drive to the draft 
inducing blower..usually a centrifugal or squirrel cage type.

Has trane gone techno and put in a brushless motor that requires a 
switching PWM drive or similar?  Surely no brushes.  But if it is a 
drive type PWM or vectored-flux motor, it could be the drive making the 
noise, not the motor.

Unless the motor just has some resonant condition where the windings 
radiate at the switch freq or harmonic.

Very curious.

Curt

Steve Toth wrote:
> Al
> I believe you are correct and this could be defined as a factory defect for the furnace.  Contacting the ARRL is a good idea - I hadn't thought of that.
>  
> I was able to find quite a few threads on the internet by searching on "radio interference Trane furnace", so you're probably correct about the strength of the claim also.
>
> I just think it's kind of crazy to have one of the most sensitive receivers ever designed, if not the most sensitive, and have it knocked completely deaf by a "eco-friendly" design flaw in a furnace.
>
>
>
>
>
>
>
> -- Steve, K7PZN 
> "Think Quickly, Speak Slowly, Work Diligently, Live Simply"
>
> --- On Mon, 3/28/11, Al Parker <anchor at ec.rr.com> wrote:
>
>
> From: Al Parker <anchor at ec.rr.com>
> Subject: Re: [R-390] High Electrical hash noise level
> To: "Steve Toth" <stoth47 at yahoo.com>, r-390 at mailman.qth.net
> Date: Monday, March 28, 2011, 2:02 PM
>
>
> Hi Steve, et al,
>     I sympathize with your dilemma.  But, isn't it so that the manufacturer of a device must comply with FCC rules regarding interference, particularly to a licensed service such as amateur radio?  A similar, but more widespread, problem has occurred with BPL.
>     If you don't get relief from the dealer/mfgr, alert the ARRL, their tech. group might have some ideas, and their legal group has been involved in this sort of thing.  You should not have to buy any special filters, etc., to be able to use your equipment.  If there is widespread evidence showing a known and ongoing problem, I think you've got some strong grounds to stand on.
> 73,
>
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
> "There is nothing -- absolutely nothing -- half so much
> worth doing as simply messing about in boats"
> Ratty, to Mole
>
> On 3/28/2011 4:26 PM, Steve Toth wrote:
>   
>> Bob et al,
>> Here's the latest:  I did some digging on the internet.  Turns out this problem has been around since 2006 with Trane and American Standard Hi-Efficiency furnaces.  The source is the fan inducer motor - they went to a new design of the motor they used.  It generates strong RFI (S9 levels) from the broadcast band all the way up through VHF and UHF - wipes out AM radios, TVs, routers, etc.
>>
>> Trane is apparently aware of the problem.  They have a shielded cabling kit that can replace the inducer motor wiring harness which acts like an antenna.
>>
>> I called the servicing dealer and the "technical expert" phone rep I talked to was clueless.  After I told her the exact problem, the source of the problem and the factory fix for the problem (with part numbers) - with her taking notes - she put me on hold.  She came back online after talking to someone to tell me "yes, there was a wiring kit that they could install but it may or may not eliminate the problem."
>>
>>     
>>> From what I researched, it appears that the shielded harness sometimes solves the problem and sometimes does not.  But from what I could tell from the posts I read, it looks like it really depends on what kind of RF ground is installed on the shielded harness and furnace and how complete the shielding is on the inducer harness that determines how effective the fix is.  If the installation of the shielded harness works the noise level has been reported to drop to minimal levels.  Right now the furnace has an electrical ground but no RF ground, so it appears I'm going to have to install one.
>>>       
>> The dealer service manager is supposed to call me back and let me know what they can do for me.
>>
>>
>> -- Steve, K7PZN
>> "Think Quickly, Speak Slowly, Work Diligently, Live Simply"
>>
>>     
>
>
>
>       
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