Topband: Furnace RFI redux

[lmlangenfeld]

If you have been following this thread, you have learned:(1) ECM blower motors 
are beginning to dominate the market. The issue isn't going away, and will 
likely become more prominent as older furnaces start needing replacement.(2) 
ECM motors either will or will not create an RFI problem.(3) At least one 
manufacturer offers its dealers an optional EMI/RFI filter kit, which helps 
reduce (but does not cure) pulsed speed controller interference.(4) Additional 
work by the homeowner may improve things further, but may or may not invite 
warranty issues.In short, there is no concise and consistent answer.  It is, 
like so many other things, highly situational -- the classic YMMV.Thanks to all 
who weighed in -- I very much appreciate it.73,Mark -- WA9ETWSent from my U.S. 
Cellular® Smartphone
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Re: Topband: Furnace RFI

[Anthony Scandurra via Topband]

PDF Resolving Furnace and A/C RFI(Radio Frequency Interference … 


73, Tony K4QE

> On Oct 4, 2019, at 9:15 AM, MrToby  wrote:
> 
> The ARRL has a 2017 presentation on their website titled "Resolving Furnace
> and A/C RFI Problems"
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Re: Topband: Furnace RFI

[ed_richardson]

Mark

 

We installed a top of the line Lennox heating and AC unit 3 years ago. The
PWM motors were a big concern of mine based on reports I had read about
online. Lennox makes an RFI kit that they will provide if requested. There
was no charge for the kit consisting of 2 toroids and an AC line filter.

 

I had the contractor order the kit when they ordered the furnace. On
installation day I asked the technician for the literature that came with
the RFI kit before they left.  I went and scanned the HF bands shortly after
they left and was disappointed to find a number of spurious signals at
discrete frequencies across the 20m - 10m bands.  These signals ranged from
S3-S7. I Couldn't find anything at 6m or above and my noise floor is so high
on 160-80 that I couldn't hear or see anything new.

 

After reviewing the literature that came with the RFI kit, I opened up the
furnace and discovered the technician hadn't installed the items correctly.
I could have fixed them but decided to call the contractor back to avoid any
warranty claim issues.  Once re-installed, the noise level dropped down to
an S1-2 worst case on 17 and 15m.

 

Not being satisfied, I went ahead and added some external 2.4" cores on all
external wires coming and going from the furnace. The end result is a very
usable spectrum with just a small handful of s0 level spurs across 17m.

 

I have been very happy with the furnace and AC units themselves. I just wish
these companies would spend the extra $10 and take care of RFI/EMI right at
the source during design and production.

 

Good luck with your search!

 

Ed VE4EAR

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Re: Topband: Furnace RFI

[MrToby]

The ARRL has a 2017 presentation on their website titled "Resolving Furnace
and A/C RFI Problems"

On Fri, Oct 4, 2019, 7:26 AM  wrote:

> Hello Rob. . .I discussed this very topic with my furnace guy yesterday
> doing annual service on my furnace.  The furnace AC blower motors are
> going
> the way of the abacus.  He said it won't be long before all furnace blower
> motors will be DC.
>
> 73. . .Dave, W0FLS
>
> -Original Message-
> From: Rob Atkinson
> Sent: Friday, October 04, 2019 5:43 AM
> To: topband@contesting.com
> Subject: Re: Topband: Furnace RFI
>
> Went through this about 2 years ago.  Firstly, define "efficient."  If
> you mean over 90%, as in one of those two stage furnaces with PVC
> handling moisture then you are consigned to having to use a variable
> speed DC motor (there are no variable speed AC motors, only speed
> settings you set manually at installation) that will cause RFI because
> it is run on variable duration square wave DC.  You will have to have
> the HVAC contractor install a manufacturer supplied hush kit, or do it
> yourself.  The hush kits are over priced and many contractors are
> unfamiliar with them and RFI.
>
> Or, you can do what I did and get a single stage 80% efficient furnace
> that runs on an AC blower and accept 10% less efficiency and get on
> with life.   Mine is around 80K BTU, not extremely big.   There are
> larger ones, or were.  I went with American Standard, an Ingersol Rand
> brand name.   There are around three companies that make all the
> furnaces; IR is one of them.  I've heard the AC blower furnaces are
> going to be history in a few years after which they'll all be high
> eff. DC because gov't is obsessed with this, but that's another topic.
>
> 73
> Rob
> K5UJ
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> Reflector
>
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Re: Topband: Furnace RFI

[daraymond]

Hello Rob. . .I discussed this very topic with my furnace guy yesterday 
doing annual service on my furnace.  The furnace AC blower motors are going 
the way of the abacus.  He said it won't be long before all furnace blower 
motors will be DC.


73. . .Dave, W0FLS

-Original Message- 
From: Rob Atkinson

Sent: Friday, October 04, 2019 5:43 AM
To: topband@contesting.com
Subject: Re: Topband: Furnace RFI

Went through this about 2 years ago.  Firstly, define "efficient."  If
you mean over 90%, as in one of those two stage furnaces with PVC
handling moisture then you are consigned to having to use a variable
speed DC motor (there are no variable speed AC motors, only speed
settings you set manually at installation) that will cause RFI because
it is run on variable duration square wave DC.  You will have to have
the HVAC contractor install a manufacturer supplied hush kit, or do it
yourself.  The hush kits are over priced and many contractors are
unfamiliar with them and RFI.

Or, you can do what I did and get a single stage 80% efficient furnace
that runs on an AC blower and accept 10% less efficiency and get on
with life.   Mine is around 80K BTU, not extremely big.   There are
larger ones, or were.  I went with American Standard, an Ingersol Rand
brand name.   There are around three companies that make all the
furnaces; IR is one of them.  I've heard the AC blower furnaces are
going to be history in a few years after which they'll all be high
eff. DC because gov't is obsessed with this, but that's another topic.

73
Rob
K5UJ
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Re: Topband: Furnace RFI

[Tim Shoppa]

Some good news/bad news intermingled below :-)

At my house we had two modern air handlers and heat pumps put in about 5
years ago.

They were high-efficiency rated and had Genteq ECM motors. Note that I call
them ECM motors, not DC motors - they have power electronics that take
regular 60Hz AC and electronically commute with semiconductors to make a
variable frequency 3-phase drive. Almost certainly they do go through DC
along the way.

The good news, is that I never noticed any RFI from the ECM motors.
Possibly because of good wiring practices in the units (they always route
AC wiring around in pairs so there is no large loop. I think some
after-market ECM blower installations made poorer choices about AC wire
routing.)

The bad news, is that the ECM motors in my units died early. They have very
poor reliability. In both cases they were under warranty. If you have to
replace an ECM blower motor outside warranty you are looking at $300 for a
used/rebuilt unit and closer to $1000 for a brand new factory module.

The good news is that these ECM blower motors die early so often that they
will almost die in warranty.

Tim N3QE

On Thu, Oct 3, 2019 at 5:42 PM lmlangenfeld  wrote:

> We are in the market for a new high-efficiency furnace, and I note that
> many (if not most) of the current models use variable-speed DC blower
> motors.  I am concerned about the potential for RFI from the speed
> controllers, and wonder if any list members have any recommendations or
> recent experience (good or bad) with such units.Tnx es 73,Mark --
> WA9ETWSent from my U.S. Cellular® Smartphone
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> Reflector
>
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Re: Topband: Furnace RFI

[Rob Atkinson]

Went through this about 2 years ago.  Firstly, define "efficient."  If
you mean over 90%, as in one of those two stage furnaces with PVC
handling moisture then you are consigned to having to use a variable
speed DC motor (there are no variable speed AC motors, only speed
settings you set manually at installation) that will cause RFI because
it is run on variable duration square wave DC.  You will have to have
the HVAC contractor install a manufacturer supplied hush kit, or do it
yourself.  The hush kits are over priced and many contractors are
unfamiliar with them and RFI.

Or, you can do what I did and get a single stage 80% efficient furnace
that runs on an AC blower and accept 10% less efficiency and get on
with life.   Mine is around 80K BTU, not extremely big.   There are
larger ones, or were.  I went with American Standard, an Ingersol Rand
brand name.   There are around three companies that make all the
furnaces; IR is one of them.  I've heard the AC blower furnaces are
going to be history in a few years after which they'll all be high
eff. DC because gov't is obsessed with this, but that's another topic.

73
Rob
K5UJ
_
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