Furnace blower RF hash

[Ed-VA3ES]

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.

[KM1H]

Go forced hot water

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

[Bill, KD0HG]

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.

[kb3ouk]

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

[ka3zlr]

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...

[W3RSW]

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.

[W1ATR]

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.

[WBear2GCR]

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

[steve_qix]

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

[Ed-VA3ES]

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!   

[WA1GFZ]

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.

[W3RSW]

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. 

[WA1GFZ]

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.

[W3RSW]

think I'll try grounding the case first  (after checking continuity with the green wire, heh, heh.)

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

[WA1GFZ]

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.

[Ed-VA3ES]

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!

[WA1GFZ]

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

[Ed-VA3ES]

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]

[WA1GFZ]

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.

[ka3zlr]

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...

[Ed-VA3ES]

You're confusing me.   Shielded BX from panel to furnace?   In one post you recommend a choke in the motor leads from the controller,

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:

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.

[WA1GFZ]

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.

[KD3CN]

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

[Jim, W5JO]

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.

[k4kyv]

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.

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.

For a quick sample, look over the January and February threads.