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Author Topic: Lennox HVAC EMI-RFI  (Read 21590 times)
QRP4U2
Member

Posts: 124




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« Reply #15 on: February 28, 2013, 03:04:36 PM »

Check ot this discussion as well:

http://amfone.net/Amforum/index.php?topic=29720.25

Phil - AC0OB
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AC0OB - A Place Where Thermionic Emitters Rule!
VE3EDY
Member

Posts: 3




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« Reply #16 on: May 24, 2013, 02:07:07 PM »

EMI Eliminated 100 %.

Please see  the article I wrote  in 2013 January Issue of QST.

Technical Correspondence :

Heating Ventalation Air Conditioning (HVAC) EMI Generation.
 
Larry,Ve3edy
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K3LRH
Member

Posts: 60




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« Reply #17 on: February 05, 2014, 09:13:19 AM »

.........I have the same problem with a YORK AFFINITY heat pump.  S9+20 on 20M, 17M and less on other bands.  The RFI  seems to be coming from the OUTSIDE FAN unit.  Currently, the supplier is in contact with YORK.  Of course, they have "never seen anything like this before" with the YORK AFFINITY units.  The tech guy said that the fan motor is an ECM type, so we'll see what happens.  I posted this in case other ops have had issues with their YORK units. I suspect that the motors are probably of GE origin.  Update will follow.

73
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WB4SPT
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Posts: 150




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« Reply #18 on: February 09, 2014, 06:16:57 PM »

Correction to my previous post, I did have harmful emissions from my Trane furnace with the variable speed induction motor on 20meters on the heat cycle.  I ended up putting a bead on each of the phases of the induction motor, AT the PCB area.  You do need to pull the three contacts out of the molex like connector to accomplish this.  Each bead took 2 turns of motor wire, and the results are great.  Further work of using a corcom at the AC inlet and beads on the thermostat wiring did little else.  It was key to attack the noise source close to the PCB, before the motor wires radiate to other wires.  I also pulled the motor wires out of the bundling, braided them together and made an effort to keep them away from other wiring.  It worked.
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KD0REQ
Member

Posts: 972




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« Reply #19 on: February 10, 2014, 10:04:44 AM »

a split bead over that entire harness at the PCB might have done it, too.  ten bucks a unit to thoroughly suppress these control boards at the factory, and nobody does it...
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WD9DMP
Member

Posts: 2




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« Reply #20 on: March 16, 2014, 09:59:34 AM »

Regarding the interference issue from furnace air handlers' ECM motors, I recently solved a similar issue.

I installed a GE Evergreen IM ECM retrofit motor in my older furnace for reduction of motor noise and more efficient constant-on fan operation. It works great for that application.

However, I found that there was some interference being generated to a VLF (5KHz - 50 KHZ) lightning detection system I have installed. I installed common-mode ferrite chokes on the thermostat wiring and motor power leads, but the EMI persisted.

The problem turned out to be harmonic distortion being introduced into the AC power lines. This is caused by the non-sinusoidal current draw by the ECM motor. The DC power supply of the motor pulls power from the AC line in two sets of pulses at each AC peak, rather than in a smooth sinusoidal manner, as with a conventional PSC motor. The current bursts were causing EM spikes to be radiated by the power line and picked up by the ferrite antennas of the system.

GE send me a very large choke to put in line with the motor hot lead. This smoothed out the current pulses and essentially cured the issue.

See this really great white paper on ECM motor harmonic distortion:

http://www.danfoss.com/NR/rdonlyres/37FCE24B-29AD-4842-8112-3C4B6DD0C183/0/HarmonicDistortionoftheACPowerLine.pdf

I also put together a report with pictures for GE in exchange for the free choke.

http://projectmf.homelinux.com/station_pics/Harmonic_Distortion_EMI_v1.1.pdf

Regards,

Don
« Last Edit: March 16, 2014, 10:02:52 AM by WD9DMP » Logged
WD9DMP
Member

Posts: 2




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« Reply #21 on: March 17, 2014, 06:04:02 AM »

I took some additional oscilloscope measurements that verified the effectiveness of the choke in attenuating the noise. New link:

http://projectmf.homelinux.com/station_pics/Harmonic_Distortion_EMI.pdf

Don
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KD0REQ
Member

Posts: 972




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« Reply #22 on: March 18, 2014, 05:31:31 PM »

Xerox had that issue with copiers in the 70s.  put a lot of EMI on the power line in the commercial building my first employer had a radio production studio in.  on request, the Xerox rep would come out and put a big old choke in the power line, solved the problem.

one of the TV engineers had a continuing issue with a big old TT70 2-inch quad VTR in the studio.  when it started recording badly, took him a week to find out it was throwing huge spikes into the line because the 50,000 uF filter capacitors in the power supply were dry.  the motors were servomotors, gen-1 huge things, driven by pulses.  he went through every spare board in the place, plus all the working ones in the main studio down in Fargo, before he finally put the scope on the power supply.  he even asked me, the lowly news guy, what I thought it looked like.
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VE3HUT
Member

Posts: 1




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« Reply #23 on: April 04, 2014, 01:29:27 PM »

Lennox has an EMI Filter Kit (Part # 604552-01) which can be obtained through a Lennox certified HVAC installer.  The kit consists of an EMI FIlter and two ferrites.  The filter goes in between the supply voltage and the IFC control board.  The ferrites are installed on the thermostat wire and on the input wire from the supply junction box.

Call Lennox and tell them that this kit does the trick!

VE3HUT
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N2FKW
Member

Posts: 1




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« Reply #24 on: April 15, 2014, 10:23:20 AM »

As others have noted this is a known problem with newer high efficiency Lennox furnaces. In my case I also noticed the correlation between the Furnace running and the terrible RFI. At first I thought that it might be the variable speed DC motor driving the blower. Further investigation (listening with a handheld AM portable radio while the furnace went through its cycle) revealed that the real culprit was the variable speed DC motor driving the "inducer" which brings in combustion air from outdoors. After consulting with the dealer which installed the unit and waiting for a few weeks, a Lennox factory engineer showed up at my house with both a "filtering kit" (ferrite beads and a AC line filter) plus a new controller board for the furnace. After a few hours the install was done and the RFI was completely gone - all at no cost to me.

Now my only "local" RFI problems are confined to faulty sodium vapor street lights that cycle on and off through the night. Finding them requires driving/walking around and noticing the cycling lights with both your eyes and and with the handheld AM portable radio. Note the pole number(s) and location of the offender and report them to your local electric utility (via phone or website). I've had good luck with my utility (National Grid) replacing the faulty units in just a few days.

73s from N2FKW
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