[TheForge] Microwave Question OT

Tue Feb 17 14:12:05 2004

Grover -- thanks for the information.
First I understand about the half wave rectifier -- and that explains the
hum at the breaker panel.
Think I will just swap out the breaker because that is very easy for me to
do.  (32 years of industrial construction experience -- and I wired this new
house and the new  shop.)  That is also why I know there is nothing else on
this breaker.  That being said -- I think it is more likely that it is a
microwave capacitor that is going bad.  It is just a lot easier to swap the
breaker first.  My industrial trouble shooting says that unless you are damn
sure of a cause -- do the easy one first before you do the brain surgery.

The clunk is right at the very start -- and that is also when the breaker
trips.  I can hear the fan start, and the softer hum of the transformer and
then hear the louder hum as the  magnetron filaments have warmed up.  Yes,
this seem to be a loud hum.  What doesn't seem to make sense to  me is why
it only does it sometimes?  The only time it will trip except at the very
start is when using it to "defrost" and I have only seen this once or twice
and it was when the magnetron was cycled back on.  We are the type of folks
that mostly use the microwave to heat up coffee or tea, heat leftovers and
defrost things.  We very seldom use the mid range settings that cycle to
give a lower average output the way the defrost does.

Thanks for the warning about the chicken stick -- just like going into the
high voltage section in the days when we used to work on TV's.  (I never
worked on TV's but my Dad did a lot in the good old vacuum tube days of the
50's and 60's.)  Always good to know that your capacitor has been
discharged.  Oh and for what it is worth Dad always called them
condensers -- that is the way he learned it in school.  He was an EE, 1933
University of Illinois.

Again Thanks and work safe,

Dave Smucker
----- Original Message ----- 
From: "Grover Richardson" <[email protected]>
To: <[email protected]>
Sent: Tuesday, February 17, 2004 10:13 AM
Subject: RE: [TheForge] Microwave Question OT

Hi there.  Just got to email.

Well, microwave ovens have a fuse inside, under the cover. If that fuse
isn't blowing, the oven likely is ok.

A microwave oven is a half wave rectifier.  So, it AVERAGES 13.6 Amps, but
actually it's one half cycle of nothing, and one half cycle of 27.2 Amps.
So, the breaker could be going soft, or there might be other items on the
breaker that are adding up the current.

An easy thing to do, would be to swap that breaker with another one of the
same rating to see if it's the breaker, and at no cost.  This is if you know
electrical panels sufficiently well to not fry yourself, or know someone to
do it for you.

Now, having said that. Your description tells more.

If it clunks exactly when you start, then there is a good possibility that
the capacitor is going bad.  Does the oven hum loudly?  This would also
indicate a soft capacitor.  Normally when you turn one on, you have the fan
cut on, and you get a small hum from the transformer.  Then, in about 2
seconds, when the magnetron filaments have warmed up, you will hear the fan
slow down and the transformer hum get louder.

Built ins can be difficult to work on (only worked on 2, and they both were
boogers<G>).

If you can get the front off, I can tell you more on troubleshooting.

DANGER WILL ROBINSON.  You will need what we call a "chicken stick."  This
is a screwdriver with a ground wire attached.  This way you can ground
everything you are about to touch, before you touch it.

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of David E. Smucker
Sent: Monday, February 16, 2004 3:43 PM
To: [email protected]
Subject: [TheForge] Microwave Question OT

Grover -- this is not about the heavy metal session OT but about my home
microwave.

It is new, less than a year old, rated at 1100 watts, max current 13.6 -- 
yet we are having trouble with it knocking out the breaker  rather often. It
is on a 20 amp breaker, no. 12 wire, with nothing else on that breaker so it
should not trip.  I have not yet changed out the break to see if it is going
bad but it was new too -- same age as the microwave.  (new house)

It does not always trip -- maybe every 10 to 15 times it is started.  Also
the microwave kind of "clunks" when starting?  can the magnetron be loose?
Also I get a heavy hum (60 hertz) at the breaker when starting.

I know I can change out the breaker, and also open up the microwave to see
it something is loose but it is a build-in and so far I have been too lazy
to do either.

Just wondering if you ever ran into this.

Dave Smucker
----- Original Message ----- 
From: "Grover Richardson" <[email protected]>
To: <[email protected]>
Sent: Monday, February 16, 2004 10:14 AM
Subject: RE: [TheForge] microwave heavy metal session OT somewhat

SNIP
_______________________________________________
http://mailman.qth.net/mailman/listinfo/theforge
theforge mail list group photo site is http://www.photoaccess.com
Login:  [email protected]
password:  anvil
___________

_______________________________________________
http://mailman.qth.net/mailman/listinfo/theforge
theforge mail list group photo site is
http://www.photoaccess.com
Login:  [email protected]
password:  anvil
___________