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THE AM BULLETIN BOARD => Technical Forum => Topic started by: Ed-VA3ES on November 27, 2008, 11:27:28 AM



Title: Furnace blower RF hash
Post by: Ed-VA3ES on November 27, 2008, 11:27:28 AM
OK you HVAC gurus, I need help on this one!

I recently installed a new Trane furnace. It’s a XV95 series (XV95TUH2B060A9V3VA).  One of the blowers (or both) is causing RF hash on most bands. It’s particularly bad on 160 and 80, and  covers up to at least 25 Mhz.    It uses an "ECM" DC motor.

Any of you HVAC gurus (hello, W1ATR?)  know where to start?  I suspect I should bypass and filter the blower motors with  .1 caps and ferrites, but would like some expert opinion.  I have the Installation manual.


Title: Re: Furnace blower RF hash
Post by: KM1H on November 27, 2008, 02:35:11 PM
Go forced hot water ;D

Ive had to do a lot of bypassing and brute force filtering here but not with a furnace. I did put a MOV inside the furnace controller to kill the turn on spike.

Carl
KM1H


Title: Re: Furnace blower RF hash
Post by: Bill, KD0HG on November 27, 2008, 04:19:41 PM
I'd start by clamping ferrites over the motor power leads.
Bypass caps may not be necessary.

There *might* be radiation from the motor's driveshaft, but I don't know how one might handle it.


Title: Re: Furnace blower RF hash
Post by: kb3ouk on November 27, 2008, 04:22:39 PM
I asked my dad, he says the ECM motors will change speed to adjust the air output, so most likely their is a computer of some kind in there controling the motor. That could be where your noise problem is coming from.
Shelby KB3OUK


Title: Re: Furnace blower RF hash
Post by: ka3zlr on November 27, 2008, 04:36:44 PM
Not trying to be a smarty here but why not isolate yer receivers from any line hash, and filter the supply at that point...it's alot easier... :)...or filter the supply to the offending device, but new things come with warranty...to break in might compromise this...


Title: Re: Furnace blower RF hash
Post by: W3RSW on November 27, 2008, 04:41:01 PM
Almost always go for the garbage source, particularly if it's accessible, single and identified. That way every future rig that comes in the house is covered.  I'm trying to think of an exception to such a potentially easy RFI elimination.


Title: Re: Furnace blower RF hash
Post by: W1ATR on November 27, 2008, 05:46:30 PM
In short, yeah, yer boned. But despite the Tryptophan nulling my synapses, we can whale on this one for a bit.

Your on the right track with the bypass caps and ferrites, but don't bother with the motor leads. Get your filtering done at the power in right after the kill switch. It's not actually the motor that's making the racket, it's the dc driver board that controls the motors' speed that's dumping it's love back into L1 and L2 and radiating throughout the house, mainly right to your RX's.

I wouldn't bother with the snapover ferrites if the sig your seeing is really strong. Go to some nice fat donuts, (I forget what mix works best right now, tryptophan amnesia), and get some .1's to ground on L1 and L2.

Making sure your radio room isn't on the same buss bar as the furnace may knock it down a bit, but there's still L2 to deal with. An iso tranny might help a bit in the shack as well.

Just treat it like you were dealing with a switching power suckply and don't do anything that changes the sine going in or the smoke may leave that motor controller. (That sucker isn't cheap.)

More to come in a bit.


Title: Re: Furnace blower RF hash
Post by: WBear2GCR on November 28, 2008, 12:07:47 AM

Check to see if anything is actually grounded. Ground it.  That includes the body of the big unit, and the body of the motor thingie...Then see...

            _-_-bear


Title: Re: Furnace blower RF hash
Post by: steve_qix on November 28, 2008, 07:01:46 AM
I have an Energy Kinetics System 2000 - Generates LOTS of hash when in use - mostly if not all from the burner itself, although there is a computer involved as well.

Oh, is this gas or oil?   Mine is oil.

I put MAJOR filtering on all lines in and out, but didn't acutally modify the unit in any way.  There was hash on everything - the thermostat wiring and AC wiring.

So, series chokes and bypass caps in all the lines really knocked it down.  I never found direct radiation from the unit itself to be an issue - the emissions were radiating from the lines going in and out.

I also have the same trouble with computer power supplies - the RF conducted into the AC line from the power supplies is generally the problem on HF.  I have modified a number of power supplies with series RF chokes and bypass caps on the LINE side of the supply (to prevent RF from getting OUT).

Generally I enjoy an interference-free environment, however from time to time a new piece of equipment will show up in the house that needs the "treatment".

It is rather amazing how much RF hash this stuff produces !  One of the worst offenders was a d-link wireless router/switch.  I couldn't fix that one (the RF was on the LAN cables), so I got a different unit.

Regards,

Steve




Title: Re: Furnace blower RF hash
Post by: Ed-VA3ES on November 28, 2008, 09:29:01 AM
All good information.  The furnace is natural gas.

Jared, I assume you mean the AC mains in, by "L1 and L2"?    I'll start by filtering the AC in, and see what transpires.  According to Steve, QIX, I may need to bypass and filter various control lines and leads. 

What fun!   ::)


Title: Re: Furnace blower RF hash
Post by: WA1GFZ on November 28, 2008, 05:55:19 PM
Steve
wind the lan cables around torroids as common mode choke. At work we found many differential line drivers do not have exactly 50 % duty cycle.
This causes phase offsets and lots of radiation. We needed around XL=500 ohms common mode to quench this noise.


Title: Re: Furnace blower RF hash
Post by: W3RSW on November 29, 2008, 09:31:00 PM
I have a Samsung plasma hdtv which really generates hash on all sw freqs.
The most obnoxious harmonics are about every 242 KHz, "S9 to S9+5"

Has anyone sucessfully RFI'd these beasts?  It came with clamp on ferrites, etc. but they don't seem to do much. 

Seems like the RFI is right out of the screen. 


Title: Re: Furnace blower RF hash
Post by: WA1GFZ on November 30, 2008, 11:38:29 AM
Try putting metal window screen in front of the display and see if anything changes. You may have to ground it. Then run really fast after you tell the family about your fix.


Title: Re: Furnace blower RF hash
Post by: W3RSW on November 30, 2008, 04:34:03 PM
think I'll try grounding the case first  ;D (after checking continuity with the green wire, heh, heh.)

Just turning the beast off clears up entire worlds of HF.


Title: Re: Furnace blower RF hash
Post by: WA1GFZ on November 30, 2008, 05:29:08 PM
I do a little work on motor controllers. We have 1 running about 1/3 megawatt. I gave a choice. Build a three phase EMI filter the size of the controller or run the motor leads down BX. They found this nice vinyl coated BX. A little machine work at each end to terminate the shield and no more radiation off the motor leads.


Title: Re: Furnace blower RF hash, solved?
Post by: Ed-VA3ES on December 27, 2008, 08:02:56 AM
Eureka!   I received an interesting and timely email from Jim, W8WRP,  describing in detail his fix for his own  Trane XV95 furnace!   Jim has provided detailed instructions  on how he solved his problem, with diagrams, pictures, and a copy of a maintenance bulletin that Trane put out  on just this RFI problem.  I've compiled the material into a document that I'm going to hand to the furnace installation people for their info and files.  I'll be implementing this fix as soon as I can clear some  warranty issues with the heating company.

Basically the fix entails the installation of an AC mains line filter on the variable speed inducer,   a shielded and beaded thermostat control cable, a grounded gas feed pipe and some other fixes.

Should anyone want this info, just PM or email me.   

Thanks Jim!


Title: Re: Furnace blower RF hash
Post by: WA1GFZ on December 27, 2008, 08:11:03 AM
A variable speed motor is a trip to quiet down. The best way is a big common mode choke on the input power leads. Take a hunk of romex or heavy machine drop and wrap it through a big core and tie in series with the power including the safety ground. I have a similar problem at work with a 1/3 mega-watt motor controller. Motor leads the best thing to do is shield them well. I would use BX cable


Title: Re: Furnace blower RF hash
Post by: Ed-VA3ES on December 27, 2008, 08:16:30 AM
If the fix as Jim presented it isn't enough,  then  what you've suggested is what I will do.   The existing feed is unshielded romex to the furnace.   We will see what transpires, but I may have to lay in some big  fat cores, and  some BX.


A variable speed motor is a trip to quiet down. The best way is a big common mode choke on the input power leads. Take a hunk of romex or heavy machine drop and wrap it through a big core and tie in series with the power including the safety ground. I have a similar problem at work with a 1/3 mega-watt motor controller. Motor leads the best thing to do is shield them well. I would use BX cable /quote]


Title: Re: Furnace blower RF hash
Post by: WA1GFZ on December 27, 2008, 08:38:23 AM
BX between the controller and motor only. Many motor controllers rely on the motor winding inductance to control current so not a good idea adding stuff between the motor and controller. Our system is closed loop with position feedback so messing with the loop may have caused problems for the controller.


Title: Re: Furnace blower RF hash
Post by: ka3zlr on December 27, 2008, 08:40:41 AM
One of the biggest reasons I bought this house...Hot Water base board heat...man it's great ....No forced air anything only in the summer for air...


Title: Re: Furnace blower RF hash
Post by: Ed-VA3ES on December 27, 2008, 12:23:48 PM
You're confusing me.   Shielded BX from panel to furnace?   In one post you recommend a choke in the motor leads from the controller,
Quote
The best way is a big common mode choke on the input power leads. Take a hunk of romex or heavy machine drop and wrap it through a big core and tie in series with the power including the safety ground.
  Then in another post you tell me not to:
Quote
BX between the controller and motor only. Many motor controllers rely on the motor winding inductance to control current so not a good idea adding stuff between the motor and controller.

What to do?



BX between the controller and motor only. Many motor controllers rely on the motor winding inductance to control current so not a good idea adding stuff between the motor and controller. Our system is closed loop with position feedback so messing with the loop may have caused problems for the controller.


Title: Re: Furnace blower RF hash
Post by: WA1GFZ on December 27, 2008, 12:35:41 PM
Just don't put BX in the common mode choke Everything else can be BX.
The BX will limit radiation off the power leads back to the panel if you want to go throught the trouble. Heck you could even put a common mode choke inside the panel before it hits the BX. BX between the controller and motor well grounded at each end. I would think it is a free running PWM driving the variable speed motor. The output is a series of square waves and the inductance of the motor makes the current a triangle. Either way plenty of noise.


Title: Re: Furnace blower RF hash
Post by: KD3CN on February 11, 2009, 08:35:17 AM

Is this hash problem common to the heating systems with variable speed fans, ro the exception???

You may have guessed it - my heatpump has crapped out, and I'm shopping for a new one.  The old one had a single speed fan with no rf noise.  The shack is about 15 ft from the air handler.

I'm looking at Carrier and Lennox.  All but the bottom-of-the-line models have variable speed fans.

If this is an uncommon problem I'll take my chances and deal with the noise if it shows up.

Thanks for any advice/experience!

Karl


Title: Re: Furnace blower RF hash
Post by: Jim, W5JO on February 11, 2009, 09:41:08 AM

Is this hash problem common to the heating systems with variable speed fans, ro the exception???

You may have guessed it - my heatpump has crapped out, and I'm shopping for a new one.  The old one had a single speed fan with no rf noise.  The shack is about 15 ft from the air handler.

I'm looking at Carrier and Lennox.  All but the bottom-of-the-line models have variable speed fans.

If this is an uncommon problem I'll take my chances and deal with the noise if it shows up.

Thanks for any advice/experience!

Karl

It seems to be.  I have a Heil heatpump with variable speed air handler and have the same noise.  International Comfort Products has not been cooperative at all with information or help, so this thread is timely information for me.  Be sure the brand you buy is not made by International Comfort Products

Then when you contract with someone, specify in the contract that they will fix any RF radiation.  My unit radiates, it is not on the power  feed to the system.


Title: Re: Furnace blower RF hash
Post by: k4kyv on February 11, 2009, 10:58:45 AM
International Comfort Products has not been cooperative at all with information or help, so this thread is timely information for me.  Be sure the brand you buy is not made by International Comfort Products

I hope you CC'ed that to the company.  If they realise they might be losing customers or sales, maybe that will give them some incentive to clean up their act.

Quote
Then when you contract with someone, specify in the contract that they will fix any RF radiation. 

Excellent idea.  And make it clear from the outset that if they refuse to accept those conditions, you will take your business elsewhere.

This mailing list might be of interest to anyone with RFI problems:
http://lists.contesting.com/mailman/listinfo/rfi

Check out the archives here (http://lists.contesting.com/pipermail/rfi/).

For a quick sample, look over the January (http://lists.contesting.com/pipermail/rfi/2009-January/thread.html) and February threads (http://lists.contesting.com/pipermail/rfi/2009-February/thread.html).



Title: Re: Furnace blower RF hash
Post by: Ed-VA3ES on February 11, 2009, 11:35:38 AM
Jim, W8WRP  has been extremely helpful in providing a virtual Trane XV95 RFI mitigation manual.  I can send the information electronically to anyone who requests it. It's a huge file, (7.4 Mb).

The furnace installation people are coming by tomorrow to install the Trane RFI kit. Jim's instructions  are far more intensive than what Trane provides. 

Most furnaces today use an ECM DC motor which is driven by a PDM pulse train. This PDM signal  propagates throughout the AC wiring, and control wiring.  The fix requires an big EMI filter at the AC input, and  ferrites on every control wire in and out. Some control cables must be shielded. I'm on nat gas, so the feeder pipe must be grounded too.  A big PITA.

I put together all of Jim's info into a bound manual, one of which I will keep with the furnace instructions, the other will be given to the furnace people.    If anyone is interested, I can be convinced to make copies for distribution.   It has all the RFI mitigation instructions,  12 photos, schematics and Trane's original RFI kit instructions.

If really  pressed, I could post the stuff here, but it would take  several postings to do a complete job.


Title: Re: Furnace blower RF hash
Post by: KD3CN on February 11, 2009, 03:12:58 PM
Thanks for the info Ed,
Unfortunately my email would choke on a file that big.
Right now I' leaning toward getting an air handling unit with fixed speed fan.  The variable speed motor sounds like asking for trouble.  Perhaps I can still get a unit with relatively high efficiency.

I'd rather have pins in the eyes than volunarily put a big (expensive) RFI source in the shack.. 

Thanks,  Karl


Title: Re: Furnace blower RF hash
Post by: K3ZS on February 11, 2009, 04:37:49 PM
I got a Trane heat pump a few years ago, however it is an add on to an oil hot air furnace.    The furnace blower has a two  speed blower, but it changes speed by changing the connections to it.    It makes no RFI at all.   The Tranes are good northern heatpumps.    The compressor and its fan are shielded (from lawn mower rocks) and the air exits on the side near the top, so you don't have to be clearing off ice and snow from the top of the compressor fan.    It provides heat down to about 10 degrees.    I have used 1/2 tank of oil since filling it up three years ago.   Just keep the thermostat up all of the time.   


Title: Re: Furnace blower RF hash
Post by: Jim, W5JO on February 11, 2009, 05:20:23 PM
The Heil system I have is all electric and I can't follow the signal down the wiring anywhere.  It simply radiates from the cabinet.

One of the money saving parts of these systems is the variable speed motor.  If you wish to save on your bill, I would consider getting the variable speed system.  The RFI generated here is not that loud and I can hear stations over it, it's just annoying.  I am told a big core with the leads from controller board to the motor will do the trick.  My service man called the technical rep who first denied it was a problem but finally told him to get a "filter" from Radio Shack and wind the power and control leads and it would solve the problem.  My problem is I don't know which "filter" and he won't tell us. 

I think I may file a complaint with the FCC just to see what they will do, maybe they will get Heil to tell my what kind of "filter".  They have been such butts about this.



Title: Re: Furnace blower RF hash
Post by: ke7trp on February 11, 2009, 06:36:01 PM
My "american standard" brand new HVAC system did this. RF chokes on the power leads fixed it. Its was the variable speed motor.

My philips HD DVD player is a lost cause. Plug it in to the wall with the power to the unit OFF and it puts out a nice 9S signal on every band. S9 +40 on the 6mhz band. No amount of filters fixed this. I just unplugged it.  When I want to watch a DVD we plug it in.

I was amazed at how much home devices put out hash on the ham bands. I have a small Sangean SW radio. I walked around the house with and found sources of noise to be the following:

ION type Air purifiers (we had two of them)
Kitchen lighting (FL type)
Carver stereo preamp.
HD DVD player was the worst.
Samsung HD TV but its livable.

With all that crap turned off my RX is nice.  Start switching stuff on and it gets worse and worse. When I talk on the AMI night, Its me with nothing turned on in a fairly dark house LOL



Clark


Title: Re: Furnace blower RF hash
Post by: k4kyv on February 12, 2009, 01:54:06 PM
I think I may file a complaint with the FCC just to see what they will do, maybe they will get Heil to tell my what kind of "filter".  They have been such butts about this.

Yeah, just tell 'em to "go to Heil".  ;D

I think one of the reasons so much consumer crap radiates garbage these days is that no-one listens to AM radio any more, except for maybe a few Rush Limpballs fans, and nearly everyone has cable TV.

I recently had a severe power line noise problem, and found the source about two miles away.  I knocked on a few doors in the vicinity, and found maybe a half dozen people home.  I asked them if they had been experiencing any radio or TV interference and let them listen to the portable radio I had with me.  The local AM BC station 8 miles away was nearly covered up by the sizzle.  Every single person I talked to told me no, they hadn't been aware of any problem, even though they were living right underneath the noise source.

A generation or two ago when most of the radio the public listened to was AM, and TV was picked up from a station 50 miles away with a rooftop antenna, this electromagnetic pollution would not have been tolerated.

If and whenever the great change-over to digital TV finally occurs, the situation will only get worse.


Title: Re: Furnace blower RF hash
Post by: Jim, W5JO on February 12, 2009, 07:40:54 PM
My "american standard" brand new HVAC system did this. RF chokes on the power leads fixed it. Its was the variable speed motor.

Clark

Which power leads Clark, the ones to the motor or the ones to the unit itself?


Title: Re: Furnace blower RF hash
Post by: KD3CN on February 28, 2009, 05:06:50 PM

Just wanted to post this info for others that might face a crapped-out heat pump.

The new unit is installed, with no rf hash problems on my receivers  (several feet away).
It is a Carrier FV4 air handler with variable (ECM) fan.  Before buying I rf-snooped a neighbor's FE4 air handler (also ECM variable fan), and heard nothing.  So I'd recommend either of these from an rf interference prospective.  ;)

73!  Karl


Title: Re: Furnace blower RF hash
Post by: Opcom on March 01, 2009, 08:41:13 PM
If you are clear in comunicating to the company trying to sell you this stuff they should be decent about it. In your case you already have it, so maybe a complaint to the FCC could help get someone's attention. You should not have to pay extra for them to fix this, nor do their engineering for them (possibly giving them a reason later to void your warranty). Hope it gets resolved soon.
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