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

dgsvetan@rockwellcollins.com dgsvetan at rockwellcollins.com
Mon Apr 11 09:51:32 EDT 2005


Thank you for the reference to my prior posting.  It is always nice to know
when someone gets some good from your efforts.

From what you have written, I would say that the Gibson washer has a
different problem than does the Whirlpool Duet.  I wrote that earlier post
before the cause of radiated noise was known; variable speed drives are
known to be prolific RFI generators, and your machine proves that point.
In your case, it sounds as if the power cord was, indeed, the primary
conductor of drive hash, and you were successful in finding a combination
of ingredients (toroids + by-pass filter) that fixed it.  You also tied the
filter's case back to the machine.  That wire is, in my mind, at least as
important as the separate ground lead, although it may have been just as
good to have taken that one back to the power panel ground.   Had you been
able to find a better low frequency material that Mix 43 for the toroids,
just oone may have worked.  However, "find" is the key word there, and it
sounds like the pair you got did the trick.

In the case of the Duet, futher RFI sniffing by the owner found the power
cord to be clean and the "hottest" area of noise was the plastic-cased
control panel area.  This goes to show that a variety of techniques need to
be applied to first determine the source of the problem, and then effect a
cure.  Good going, and thanks for the post.  Sorry to hear about the water
leak problem.

Note:  my wife was looking at the Duet during a recent visit to a Lowe's
store.  She knows about the RFI problem with them (she is also a ham who
works HF), but likes the features.  Next to the Duet was a pair of high
efficiency machines (washer and dryer) from Bosch.  Anyone know anything
about those as RFI sources?

73, Dale

             "Scott M. Yost"                                               
             s at charter.net>                                             To 
             Sent by:                  <rfi at contesting.com>                
             rfi-bounces at conte                                          cc 
                                       [RFI] Washing Machine RFI - at      
             04/08/2005 05:55          least one case solved               

Washing Machine RFI - at least one case solved

We have a Gibson front loading clothes washer which was the most prolific
generator on the planet.  It blanketed MF through HF when running, and not
radios inside the house.  It actually would wipe out my 40m mobile, parked
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
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
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
F240-43 toroid core.  About 6 inches further along the cord I wound another
turns through a second F240-43 core.  This was the maximum number of turns
could wind on each core due to the size of the AC plug.  (For possible
service reasons, I did not want to remove the AC plug while winding the
although that would have made it easier.)  The first and last turns on each
are separated as much as possible to prevent capacitive coupling which
bypass the winding's beneficial effect.  So to clarify: the washer power
has 2 separate toroid cores, each wound with 7 turns and spaced about 6
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
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,
the cores on the I/O wires right at the controller PCB inside the washer
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
alarm goes off…

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

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