There's some un-necessary reinvention of the wheel here, as well as some
blank spots in how motors work, including those in refrigerators.
Two of the most important pieces of test equipment are clamp-on AC
ammeter and current probe, and a short AC jumper with the outer jacket
stripped for a foot or so to allow the ammeter to be clamped around one
conductor at a time. The current probe hooked up to a scope lets us
study the waveform. Even the very useful Kill-A-Watt tester provides a
LOT of information about what's happening on Phase and Neutral.
Using any of these devices to monitor current when the fridge is first
plugged in, then a minute or two later, would quickly reveal that the
motor draws a lot of current to start the motor, not a lot after that.
As to the choke -- there's a LOT of practical info on my website based
on long term study of common mode chokes for the MF, HF, and even VHF
bands, combined with many hundreds of hours in the lab measuring
practical chokes. The most detailed data is for TX chokes; there's also
data for chokes for RX antennas for the lower ham bands. The TX choke
data can serve as a starting point for power line chokes using
comparable sized cable; there's also a long tutorial app note about
identifying the sources and killing the sort of noise you've encountered
here.
And there's a tutorial on how ferrite common mode chokes work. First
published in 2007, it's had millions of downloads. k9yc.com/RFI-Ham.pdf
One important principle -- it's NOT inductance that does the work, it's
the RESISTANCE at the parallel resonance of the choke. Study the data
sheet for Fair-Rite parts designed for suppression at VHF -- they show
the parallel resonance for 1, 2, and 3 turns. When I did research for an
AES paper on suppressing RFI to audio systems that I published in 2005,
I found concepts in app notes from the '50s that made it clear they knew
about this then. And US Army labs knew about it in the '70s -- after an
EE supervisor from CIA heard me present these concepts at Pacificon c.a.
2010, he sent me a non-classified engineering report making use of
exactly the techniques I'd discussed.
73, Jim K9YC
On 10/1/2020 5:22 PM, David Eckhardt wrote:
I wish I could include images with the group.io groups, but can't. Using
the HP 8753C, I selected the large ferrite toroid which gave the best
performance at 160-meters and above using a single turn clip lead through
each candidate core.
I was concerned about the recommendation in the manual that a circuit fused
(circuit broken) for 15 to 20 amperes was necessary. HitchenAid also
recommended against use of an extensiion. All this lead me to believe the
unit drew upwards of 15+ amperes at 120 vac, So, I went overboard using
AWG #12 stranded wire for the CM choke. Then I get behind the frig to
install it, and find the cord on the back is only AWG #18. Would have been
much easier to have just used a butchered cord. Well, here is the solution
(no picture). The CM choke measured 146 + j322 at 1.78 MHz when completed
with three turns through the core (including the 'green' conductor).
Problem solved. I still have a little 60 Hz garbage on 160-meters from
elsewhere, but this totally took care of the frig. RFI. And how many
problems have I solved while still working by simply adding the CM choke
that should have been there in the first place? TOO MANY....... Darn
contract manufacturers!
Once again, I'm a happy camper and thankful I have a functional RF lab.
BTW: KitchenAid claims "Made in the USA" (of foreign and domestic parts).
Dave - WØLEV
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