[RFI] Washing Machine RFI - at least one case solved

Scott M. Yost northernradiolabs at charter.net
Fri Apr 8 18:55:08 EDT 2005

Washing Machine RFI - at least one case solved

We have a Gibson front loading clothes washer which was the most prolific RFI 
generator on the planet.  It blanketed MF through HF when running, and not just 
radios inside the house.  It actually would wipe out my 40m mobile, parked out 
in the driveway.  I tinkered with the problem off and on, and finally struck on 
a combination to solve it.

Before I start, standard disclaimer:  if you undertake this, you do so at your 
own risk, and I make no warranty whatsoever.  

I'd determined the noise originated in the unit's motor controller, and was 
being radiated by the house wiring.  This was reinforced on reading an excellent 
post by WA9ENA from 04 JAN 2005.  I suggest also reading that post.

My RFI suppression method follows: starting close to the AC power cord's exit at 
the back of the washer, I wound the cord 7 times through a Palomar Engineers 
F240-43 toroid core.  About 6 inches further along the cord I wound another 7 
turns through a second F240-43 core.  This was the maximum number of turns I 
could wind on each core due to the size of the AC plug.  (For possible future 
service reasons, I did not want to remove the AC plug while winding the cores, 
although that would have made it easier.)  The first and last turns on each core 
are separated as much as possible to prevent capacitive coupling which might 
bypass the winding's beneficial effect.  So to clarify: the washer power cord 
has 2 separate toroid cores, each wound with 7 turns and spaced about 6 inches 
apart.  Overall, this takes up about 90% of the cord's length.  

That cord is plugged into a cast-aluminum cased ISOBAR "Noise Filter and Surge 
Suppressor" 2 duplex-outlet power strip.  (It's old - model unknown. 
 Internally, it has some MOV's, several bypass caps and toroids.)

Then, for good measure, I ran a separate ground wire from the cold water line to 
the washer cabinet, and the ISOBAR.

Results: The noise is now gone, from AM BCB through HF.  I do note it yet at a 
very low level in the LF band.  

Note: neither the cores, nor the ISOBAR, were effective alone.  Also, placing 
the cores on the I/O wires right at the controller PCB inside the washer cabinet 
did not help.  (I could only get 1 turn on each core.)  With my final method I 
work entirely outside the washer's cabinet - a benefit.

In spite of solving the Gibson's RFI problems, I would not buy another.  It is 2 
½ years old and leaks at the drum flange, and that part is out of warranty 
already.  I have to tighten the drum bolts every few months, or when the H2O 
alarm goes off

But I'm happy with one thing: our clothes washer no longer runs me off the air. 
 Good luck and 73,   Scott NM8R

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