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[Articles Home]  [Add Article]  

RFI Mitigation in Rheem RGFG High Efficiency Furnace

from Don Kiser, AC2EV on June 30, 2014
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RFI Mitigation in Rheem RGFG High Efficiency Furnace

Through innovation and modern design techniques today’s home furnaces contain a multitude of electronics and technology. Gone are the days of a single phase 110 motor, a few relays, and thermal switches. Today’s furnaces use on board computers that utilize high speed data networks, continuously variable gas valves and 3-phase motors all of which are suspect to produce RFI. In this document I will show you the methods I used to locate and mitigate the main source of RFI in my furnace.

Legal
I am not a HVAC installer your situation may vary from mine. Your first action should be to contact your installer and have them contact the manufacturer to see if they offer a RFI kit to suppress the noise. If you find that you want to do it yourself, you agree to hold me harmless. I take no liability for any information you find here. Always use good engineering practices and common sense. Do not defeat any safety mechanisms in your furnace.

My Experience
When I first experienced this issue I immediately contacted my installer. They were responsive at first but I found my concerns soon fell on deaf ears with both my installer and the furnace manufacturer.

It was only after I contacted the manufacturer of the suspect devices that I was able to get useful information. However, you should always start with your installer and escalate from there. The OEM manufacturer typically does not have the resources to assist the homeowner. They make and sell the motor they don’t know how their customers (furnace manufacturer) will use them.

In my case, Rheem used a 3-phase motor on a single phase furnace. This implementation was not the responsibility of the motor manufacturer.

You may find that the part numbers on the devices do not match the manufacturer’s part numbers so be very careful in making assumptions as to what device you have.

What is RFI
Radio Frequency Interference (RFI) is radiated or conducted electrical energy that causes undesirable effect on nearby equipment.

Conducted RFI is typically in the 10 kHz to 30 MHz (160-6 meters). Radiated RFI is in the 30 MHz to 10 GHz (VHF and above).

Reading Material
Some helpful links you may or may not have read. Don’t worry there won’t be a test.

http://audiosystemsgroup.com/RFI-Ham.pdf
http://www.nccc.cc/pdf/ferrites_rfi-nccc.pdf
https://www.osha.gov/SLTC/radiofrequencyradiation/electromagnetic_fieldmemo/electromagnetic.html
http://www.arrl.org/radio-frequency-interference-rfi
http://www.nsarc.ca/hf/rfi_rev_a.pdf

RFI Suppressing Tools

Ferrite EMI Supression Cores: Fair-rite Mix 31
Mouser PN 623-0431164181
Mouser PN 623-2631102002

Power Line Filters
Corcom PN 20AYO1 – 20 Amp 3 phase WYE
Corcom PN 20EP6 – 20 Amp Single Phase

RFI Sources
There are many potential sources for RFI in a modern day furnace; the likeliest culprits involve the modulation of data or electric signals of which there are many. In my furnace these boiled down to the following possibilities:

1. Rheem RHC-TST412MDMS Communicating Thermostat
2. White Rodger 36J27-503 Modulating Gas Valve
3. Gentec (Owned by Regal-Beloit America) ECM 3.0 1/2HP 120/240V Variable Speed Blower Motor
1. Fasco (Owned by Regal-Beloit America) 70920285 3-phase Inducer

RFI suppressing methods
Locating the source of the noise can be the most difficult thing. I use the divide and conquer method. Start at the main panel in your home and begin turning off the breakers until you locate the one that reduces the RFI of interest. You may find that you have several RFI sources in your home.

With regards to locating what exactly in the furnace is the causing the RFI, this will be an exercise in trial-and-error. Maybe you’ll get lucky and fix it the first time or maybe like me, you’ll end up trying several things to find the one that works best.

At this point I must stress good engineering techniques and commonsense are necessary. It is very important to think about what you are doing and what may happen. Hypothetically speaking, one should not simply disconnect the power to the draft inducer when the furnace is running as this could cause the furnace to lose draft and result in a flame rollout. Flame rollout could cause the thermal fuses to trip. Some thermal fuses are one time use and can be expensive to replace. Otheres are resettable. Depending on your furnace, you may be able to disconnect the draft sensor which should disable the igniter loop and gas valve. Be safe, refer to the legal disclaimer.

These are guidelines, not absolutes, so feel free to experiment:

Place the power line filter closest to the control end to reduce the antenna effect of the wiring to the device.

Twist the wires from the filter to the motor. This will help to balance the electromagnetic fields and reduce RFI.

Ferrite chokes on individual wires to reduce noise. Remember the choking impedance increases by the square of the turns. At HF this will require on the order of 5 turns or more. The more turns the better. Get a bigger ferrite if needed or use several in series.

Use shielded where possible. Try grounding the shield at one end leaving the other shield un-connected or connect both ends. Try terminating the shield to the chassis vs the ground wire.

My RFI
Below is a picture of the RFI from my furnace. The lower part of the image is when the furnace was running. The middle part is when I flipped the main power on the furnace from on to off. I think we can all agree that something in the furnace was generating RFI.


Figure 1 40m RFI

This noise covered just about the entire 40 meter band and could be heard all the way up to 20 meters. At first I suspected the main blower motor, a Genteq variable speed blower. To test this, I simply started up the furnace then pulled the power connector off the blower. Result: The noise level was unaffected.

Next on the list was the gas valve. This also proved to not be the culprit. At this point I was out of ideas as I unaware the draft inducer was 3-phase and still waiting on word back from my installer.

I then reached out to the manufacturer of the motors. A few days later, I received an email from a very nice guy who turned out to be a fellow ham. I provided him the pertinent information on the motor and a few days later he replied with what he found. It turns out the draft inducer was actually a 3-phase motor. We surmised that the furnace was generating a 3-phase signal to run it. As such the signal was probably full of harmonics.

I looked again at the schematic on the furnace panel and found the inducer control board. Like everything else in the furnace it was unshielded and the motor control wires were in the same bundle as everything else.

So, I turned on the furnace and looked at my Panadapter. The noise was there. I held my breath and disconnected the power to the motor. I then saw the Panadapter go black. I found the culprit. Now I had to figure out how to make it quiet.

I picked up a 3-phase line filter, molex pins, a couple molex connectors and some shielded 4-conductor wire from various sources on the internet. Once I had all the parts I proceeded to make a plan.

Next to the OEM cable assembly I found an unused hole that was capped. I removed the cap and found a suitable cable gland.

Note: Having a high efficiency furnace means there is isolation between the combustion side and circulation side. You must ensure that you maintain this isolation otherwise you run the risk of allowing Carbon Monoxide into your home.

After installing the cable gland I ran 4-conductor shielded through the gland and attached the Molex connectors on each end. Routing of the wire depends on your furnace. Take care to avoid the sharp edges of the furnace metal. Some molex pins are better than others. I found that the female molex pins I purchased were not manufactured to the highest tolerance. I had to use a small awl or screwdriver to open up the male molex ends so that they make contact in the female sockets. A bad connection could cause erratic operation and even more RFI.

Originally I had wired this through a 3-phase power line filter but found that this caused the inducer control board to fault and not drive the inducer motor. This was evidenced by a red blinking LED on the inducer control board.

With the 4-conducter wire in place and the furnace back together I turned the power back on and started the furnace. The RFI from the furnace was gone. Problem solved. Now on to tackling the next RFI source.

Pictures


Figure 2 Cable Gland


Figure 3 Watch those sharp edges


Braid the power wires to balance the currents and reduce noise and antenna effect
Figure 4 Inducer power connector


Shield and ground are attached. Try it without shield too (at one end). One way may work better
Figure 5 New 4 conductor shielded


Figure 6 3-phase filter


Figure 7 Inducer Motor


Figure 8 New wiring, old connector abandoned in background


Figure 9 Inducer Control Board, new connector on left side

Member Comments:
This article has expired. No more comments may be added.
 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by W8AAZ on June 30, 2014 Mail this to a friend!
This is sadly probably typical in 2014. With any object powered by electricity that you bring into your home now, it's a toss-up whether your rig will hear it. No longer appears to be any preemptive testing or enforcement of FCC rules, at least not in cheap imported items. With fewer people getting over the air broadcasts, maybe they can get away with it without stirring complaints or having the consumer realize what is the problem.
 
Caution  
by DL8OV on June 30, 2014 Mail this to a friend!
The secret of being a good engineer is to know your limits (and of course know when to walk away). Gas appliances such as furnaces are one case where extreme caution should be exercised, the engineers who work on them are (or should be) certified to carry out the work.

An induced fault in the ventilation path such as disturbing a fan connection may result in carbon monoxide generation, a gas which can be deadly.

A loose or punctured gas fitting or pipe could create a gas leak.

Alterations to your furnace could void your home insurance and/or upset your local fire department.

Whilst I applaud the RFI hunting skills of the article author a far better way to achieve this task would be to call out a furnace engineer, to work with them in the elimination of the problem, and to let the furnace engineer safety test the furnace before it is put back into operation.

http://www.dailymail.co.uk/news/article-2327039/Newark-blast-Was-fatal-explosion-caused-father-trying-fit-new-central-heating.html

Peter DL8OV

 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by AI2IA on June 30, 2014 Mail this to a friend!
I admire Don, AC2EV, for posting this article. It is already evoking very interesting comments. He at the very least, brings a problem to the surface and by doing so gives others an opportunity to add comments that enrich the information. This is the kind of article that should appear most often on eHam.net. It gives us a lot to think about, and I am sure that by the end of the thread, and I hope that it is a long one, there will be collected advice and useful opinions not only applicable to this problem, but also for general use in other similar problems.
Thanks for the article, Don.
Vy 73,
de Ray, ai2ia
end of message
 
RE: RFI Mitigation in Motor driven appliances...  
by AF6AU on June 30, 2014 Mail this to a friend!
This issue with (it seems all)3 phase variable speed motors, used with an on-board integrated variable frequency drive, is becoming more commonplace. As you experienced, the newer furnaces, but also washing machines and clothes driers as well. My 4 year old front loading whirpool clothes washer has the very same thing, and uses single phase power, to charge an electrolytic capacitor, that discharges through a 3 phase variable frequency drive that allows variable drum speeds, controllable acceleration, and drum reversing for this front loader. When it's running, the RF it makes is a 'Zipping" sound on 20 meters and below, that changes pitch and cycles on-off every 5-10 seconds or so, as the drum turns, stops, reverses, etc. I used salvaged toriod rings from computer power supplies around the motor leads at both ends, and 3 of those clip-on ferrites that you use to get with computer monitors on the power cord. Since a washing machine is pretty well enclosed in metal, I optimised the metal grounding with a handful of star lockwashers on every screw I found. I cut the noise from S-12 down to S-3 or so.

My next RFI nemisis is AT&T U-Verse television, networked over the telephone lines. Their carriers begin in the lower HF band, around 3MHz and you find the buzzing peaks all over the HF band at S-7 to S-13+.

I got rid of AT&T U-verse TV, but still have their internet. Have Hughes/Direct-TV Satellite now. That helped that a lot, but I still get some noise from the rear neighbor's AT&T Uverse @S4-5. Calls to AT&T brought out the service truck and a new balun and ferrite lumps over the in-house CATV lines for the neighbor's. Improved, but not gone. Funny how the RFI goes down a little more with each subscriber lost to the satellite guys.... Keep up those U-Verse price increases AT&T.

73
AF6AU
 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by WB0OEW on June 30, 2014 Mail this to a friend!
I would like to make sure I understand that last step.

You found RFI was reduced by disconnecting the draft inducer motor. You then surmised the radiation was occurring because the wires to the motor were unshielded and bundled with other lines. Your solution was to separate these wires from the bundle and run them in a separate shielded cable. No ferrites were required. Is this correct?

Thanks.
 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by K1FPV on June 30, 2014 Mail this to a friend!

"I got rid of AT&T U-verse TV, but still have their internet. Have Hughes/Direct-TV Satellite now. That helped that a lot, but I still get some noise from the rear neighbor's AT&T Uverse @S4-5. Calls to AT&T brought out the service truck and a new balun and ferrite lumps over the in-house CATV lines for the neighbor's. Improved, but not gone. Funny how the RFI goes down a little more with each subscriber lost to the satellite guys.... Keep up those U-Verse price increases AT&T.

73
AF6AU"

Hi Jon,

Didn't know if you were aware of it or not, but I'm pretty sure I saw on the news a short time ago that AT&T bought DirecTV from Hughes. I was quite unhappy with DirecTV but must admit, I love Dish Network since I dropped DirecTV. Being a retired broadcast engineer, I saw that DirecTV was compressing the video too much and have much sharper video with Dish Network.

Regarding RFI, I had a similar situation with my Rheem hot water tank. I had to build up my own RFI choke for the 120VAC line coming into it and also had to use clamp-on RF chokes on the thermostat control wire at the tank.

My situation wasn't apparently as severe as the authors RFI case.

Bill
K1FPV
 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by KC9YTJ on June 30, 2014 Mail this to a friend!
I'd love to see the schematic for that furnace. What leads you to believe that the motor is actually a three-phase motor?

Split-phase, two-speed, I'd believe (I think the draft inducer on my Carrier furnace is a two-speed, FWIW). But using three-phase for a motor that small makes no sense. The cost of such a thing (and the three-phase converter you'd need in the circuit to power it) would have the bean counters at Rheem tearing their hair out.
 
RE: RFI Mitigation in Motor driven appliances...  
by NV5E on June 30, 2014 Mail this to a friend!
AF6AU,had the same problem with U-verse here when they ran an ethernet cable from the modem to the box at the TV. Replacing it with a shield CAT-6 cable completely eliminated the problem. Bought new cables for my neighbors too. I can still pick up (weakly) the signature U-verse interference from a condo complex a few blocks away when I point the beam at them. Not strong enough to bother me though.
 
RE: RFI Mitigation 3 phase and TV, a reply  
by AF6AU on July 1, 2014 Mail this to a friend!
I know, the focus is appliances (primarily the heating system), but RFI comes from all sorts of sources, so I had to mention U-verse...

Did not mean to create a rabbit trail thread.. Please forgive me. I will answer replies.

Yes I know AT&T bought direct, no changes (yet) so sticking there for now.

I failed to mention, the neighborhood has twisted pair copper for the wired telephone service and U-verse. Not Fiberoptic. I never hear issues in newer fiberoptic neighborhoods.

BTW my QTH CATV system is wired with double shield RG6. I replaced it all with straight no-break runs to a central location in the garage, looking for cures. The RFI was heavy on the shield. Ferrites, new system balun, new Telco drop/fuse/terminal box, new grounds, all helped some, but RFI coupled to the AC lines, and the conventional telephone lines too.

Direct's installation even re-used some of the old RG6 run, no issues. Just different frequencies, and different equipment.

This QTH is a typical single home medium dense neighborhood. You should hear the bands here on Christmas Day with all the new R/C toys and fresh batteries.... OMG!!!

I use a Sangean ATS-803 portable shortwave receiver as a sniffer. Handy thing...

Back to the article main topic, single phase to 3 phase drives, commonly noisy as I found. However look beyond the HVAC/Heater. These drives are propagating, the washing machine, clothes dryer, exercise treadmill, maybe the vacuum cleaner as well. I would expect dish washers as well in time.

It's RFI war out there...

JML
AF6AU
 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by VA7CPC on July 2, 2014 Mail this to a friend!
[quote] . . .
I admire Don, AC2EV, for posting this article. . . . . . . This is the kind of article that should appear most often on eHam.net. It gives us a lot to think about, and I am sure that by the end of the thread, and I hope that it is a long one, there will be collected advice and useful opinions not only applicable to this problem, but also for general use in other similar problems.
Thanks for the article, Don. [/quote]

+1 !

. Charles
 
RE: RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by K9COX on July 3, 2014 Mail this to a friend!
Don't think of it as a three phase AC motor, but as a brushless DC motor http://en.wikipedia.org/wiki/Brushless_DC_electric_motor
 
RE: RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by K9MHZ on July 3, 2014 Mail this to a friend!
>>>>by AF6AU on June 30, 2014 This issue with (it seems all)3 phase variable speed motors, used with an on-board integrated variable frequency drive, is becoming more commonplace. As you experienced, the newer furnaces, but also washing machines and clothes driers as well. My 4 year old front loading whirpool clothes washer has the very same thing<<<<



Yep, same deal here. PITA, and they don't care.
 
RE: RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by WA1RNE on July 3, 2014 Mail this to a friend!
by KC9YTJ on June 30, 2014

I'd love to see the schematic for that furnace. What leads you to believe that the motor is actually a three-phase motor?

>> I believe the Fasco Draft Inducer does in fact use a 3 phase motor. Everything I'm able to tell from the manufacturers web site and others, the motor assembly is fed with a 3 phase input, likely supplied by a 3 phase inverter within the furnace. An on-board 3 phase controller is built into the motor which is replaceable.

This scheme takes advantage of a more powerful motor along with a lower current 3 phase inverter to control it.


...WA1RNE
 
RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by W5JO on July 9, 2014 Mail this to a friend!
Imagine the frustration of someone who does not have the ability or equipment to do this job. Also the author didn't really cover what a manufacturer's tech people will do. They will hang up when they find you are a home owner and not a dealer. Also the FCC is no help at all.

If the system is new then doing modifications can void the warranty. Should you be considering a new air handler, I suggest you find out which causes problems and which do not by having the sales group prove and guarantee no interference before buying. Then specify you will retain 10% of the contract money until you have verified it does not cause RFI.
 
RE: RFI Mitigation in Rheem RGFG High Efficiency Furnace  
by KD0RNA on July 10, 2014 Mail this to a friend!
I'm a HVAC installer and service tech three phase motors with A/C to D/C inverters are becoming quite common in the industry,and the have been known to cause RF problems.
Thanks and 73
 
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