What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

Bobo wrote:

What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

Hmm,
Maybe switch is intermittent. There is no guarantee new switch is 100%.

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor

"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor


But how can this happen occasionally?

On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:


"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor


But how can this happen occasionally?


Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,

"Bobo" wrote in message
...
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:


"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor


But how can this happen occasionally?


Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,


That is a possibility, but the explanation given the circumstances does not
fit. Switching the active to the other terminal will reverse rotation
permanently, not occasionally.

"Bobo" wrote in message
...
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:


"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor


But how can this happen occasionally?


Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,

I believe an intermittent or failing starting capacitor has been known to
cause intermittent reverse starting of lightly loaded motors. There seems to
be some validity to the theoretical explanation of how this can happen. I
would certainly try replacing the capacitor.

Don Young

On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
wrote:


"Bobo" wrote in message
.. .
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:


"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor


But how can this happen occasionally?


Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,


That is a possibility, but the explanation given the circumstances does not
fit. Switching the active to the other terminal will reverse rotation
permanently, not occasionally.

But he's stopped talking about switching the actived to the other
terminal.

His words just above yours are "as a capacitor failed".

That might be intermittent.

Don Young wrote:
"Bobo" wrote in message
...
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:

"Telstra" wrote in message
...
"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor

But how can this happen occasionally?

Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,

I believe an intermittent or failing starting capacitor has been known to
cause intermittent reverse starting of lightly loaded motors. There seems to
be some validity to the theoretical explanation of how this can happen. I
would certainly try replacing the capacitor.

Hm - not sure. Depends on the exact type of capacitor motor. Capacitor
start only shouldn't run at all if the cap is bad, as there's no phase
shift in the armature windings. A cap-start, cap-run with a bad start
cap, now... that could very well be a reverse start, depending on how
much phase shift you wind up getting on the main field with the run cap.

I would strongly recommend having the motor checked over by a electrical
shop with motor specialisation - I'm going on fuzzily remembered motor
theory here.

Yours aye,
W. Underhill

--
"Take sides! Always take sides! You may sometimes be wrong - but the man
who refuses to take sides must *always* be wrong! Heaven save us from
poltroons who fear to make a choice!" R.A. Heinlein, "Double Star"

"mm" wrote in message
...
On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
wrote:


"Bobo" wrote in message
. ..
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:


"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same
time
the switch went bad. I put in an identical switch and didn't mess
with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the
motor


But how can this happen occasionally?


Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,


That is a possibility, but the explanation given the circumstances does
not
fit. Switching the active to the other terminal will reverse rotation
permanently, not occasionally.

But he's stopped talking about switching the actived to the other
terminal.


Okay, poorly worded question. How would a switched connection cause
occasional reversal? Is that better?

His words just above yours are "as a capacitor failed".

That might be intermittent.

On Jul 14, 1:00 am, "Mike Dobony" wrote:
"mm" wrote in message

...



On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
wrote:

"Bobo" wrote in message
. ..
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:

"Telstra" wrote in message
...

"Bobo" wrote in message
om...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same
time
the switch went bad. I put in an identical switch and didn't mess
with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the
motor

But how can this happen occasionally?

Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,

That is a possibility, but the explanation given the circumstances does
not
fit. Switching the active to the other terminal will reverse rotation
permanently, not occasionally.

But he's stopped talking about switching the actived to the other
terminal.

Okay, poorly worded question. How would a switched connection cause
occasional reversal? Is that better?

His words just above yours are "as a capacitor failed".

That might be intermittent.

Thought. Let's say the start cap is intermittent or failed and there
is a thermal draft rotating the blades. Applying power...the motor
will continue in that direction.

On Jul 13, 4:57 pm, Bobo wrote:
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

Which brings up a question I've always wondered about: why do most
microwave oven turntables randomly reverse direction at turn-on?

Red

On Jul 14, 8:17 am, Red wrote:
On Jul 13, 4:57 pm, Bobo wrote:

What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

Which brings up a question I've always wondered about: why do most
microwave oven turntables randomly reverse direction at turn-on?

Red

This is from memory...so bare-in-mind. A shaded-pole motor uses a
small induction current with very slight torque. These can start in
the opposite direction in small factors (size or sise for the english-
types 8^p)

On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:


"Telstra" wrote in message
...

"Bobo" wrote in message
...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same time
the switch went bad. I put in an identical switch and didn't mess with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the motor


But how can this happen occasionally?


I remember finding an old rotating Christmas-tree stand that would
start in either direction (randomly). This seems to be the natural
condition of some motors.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

On Sat, 14 Jul 2007 06:14:24 -0700, wrote:

On Jul 14, 1:00 am, "Mike Dobony" wrote:
"mm" wrote in message

...



On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
wrote:

"Bobo" wrote in message
. ..
On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
wrote:

"Telstra" wrote in message
...

"Bobo" wrote in message
om...
What's up with a third horse whole house fan motor that has begun to
occasionally run backwards. This started happening about the same
time
the switch went bad. I put in an identical switch and didn't mess
with
the motor wiring. It's AC, 120.
Thanks

The Fan motor capacitor has two terminals each terminal connected
to a motor winding and one also connected to the Active. Switching
the Active to the other terminal will reverse the rotation of the
motor

But how can this happen occasionally?

Googling I've found one reference to a motor running backwards
sometimes as the capacitor failed, I haven't found even one more
mention of this though,

That is a possibility, but the explanation given the circumstances does
not
fit. Switching the active to the other terminal will reverse rotation
permanently, not occasionally.

But he's stopped talking about switching the actived to the other
terminal.

Okay, poorly worded question. How would a switched connection cause
occasional reversal? Is that better?

His words just above yours are "as a capacitor failed".

That might be intermittent.

Thought. Let's say the start cap is intermittent or failed and there
is a thermal draft rotating the blades. Applying power...the motor
will continue in that direction.

You might have it there. I was surprised how much wind was blowing in
the attic when I crawled up there to look at the thing. It sits right
under a ridge vent. I got it to run the right way by starting the fan
in the right direction with a stick and then turning it on.

"I remember finding an old rotating Christmas-tree stand that would
start in either direction (randomly). This seems to be the natural
condition of some motors."

That type is a syncro-timer motor. There is a cog or detent that gets
sticky or worn that allows it to run in the opposite direction.
When it starts in the direction that is not desired...it hits the arm
or cog...and bounces back to the correct direction.

"Butzmark" wrote in message
...


Thought. Let's say the start cap is intermittent or failed and there
is a thermal draft rotating the blades. Applying power...the motor
will continue in that direction.

You might have it there. I was surprised how much wind was blowing
in
the attic when I crawled up there to look at the thing. It sits
right
under a ridge vent. I got it to run the right way by starting the
fan
in the right direction with a stick and then turning it on.


Sounds like a cap problem to me.

Bob

Sounds like a cap problem to me.

Bob

Daaaaaaah, yah think?

On Jul 14, 2:03 pm, wrote:
Sounds like a cap problem to me.

Bob

Daaaaaaah, yah think?

It may also be the centrifugal start switch is not making contact for
the start winding. It can be replace by a solid-state device if
faulty. Or replace/clean the contacts.

writes:

That type is a syncro-timer motor. There is a cog or detent that gets
sticky or worn that allows it to run in the opposite direction.
When it starts in the direction that is not desired...it hits the arm
or cog...and bounces back to the correct direction.

Microwave oven turntable drive motors are also synchronous motors which
run in either direction. But the oven doesn't care which direction the
turntable goes, so the motor doesn't need the reversing mechanism.
Sometimes the turntable goes one way, sometimes it turns the other way.

Dave

Red writes:

Which brings up a question I've always wondered about: why do most
microwave oven turntables randomly reverse direction at turn-on?

It's a synchronous motor that runs equally well in both directions, and
the direction it goes is effectively random. (You could likely get it
to always start in a particular direction by picking the point during
the AC waveform to turn on the relay supplying power to the motor).

Did you ever wonder why, if you select 45 seconds of heating, the
magnetron runs for 45 seconds but the motor continues to run for another
5 seconds after the magnetron is off? Because the turntable motor
always runs for an integer multiple of the turntable rotation period,
usually 10 seconds. So if you put something at the front of the
turntable, near the door, it will be in that position again when the
oven shuts off.

Dave

On Tue, 17 Jul 2007 06:00:07 +0000 (UTC), (Dave
Martindale) wrote:

Red writes:

Which brings up a question I've always wondered about: why do most
microwave oven turntables randomly reverse direction at turn-on?

It's a synchronous motor that runs equally well in both directions, and
the direction it goes is effectively random. (You could likely get it
to always start in a particular direction by picking the point during
the AC waveform to turn on the relay supplying power to the motor).

Did you ever wonder why, if you select 45 seconds of heating, the
magnetron runs for 45 seconds but the motor continues to run for another
5 seconds after the magnetron is off? Because the turntable motor
always runs for an integer multiple of the turntable rotation period,
usually 10 seconds. So if you put something at the front of the
turntable, near the door, it will be in that position again when the
oven shuts off.

If only. I have junk piled in front of the microwave, and I wish it
would stop in the same position it started.

I've been trying to keep track of how long a rotation takes, but I
forget now. Should I make some tests? Does it matter what brand of
microwave I have? From what you say, it doesn't seem to.

My impression is that it continues to run while it is beeping. I can
tell when the magnetron turns off by running a radio on a fairly weak
station next to the oven. Which I do a lot of the time, because I
listen to two stations 50 miles from here.

Dave

mm writes:

If only. I have junk piled in front of the microwave, and I wish it
would stop in the same position it started.

I've been trying to keep track of how long a rotation takes, but I
forget now. Should I make some tests? Does it matter what brand of
microwave I have? From what you say, it doesn't seem to.

Yeah, it would depend on brand. All the ones I've had with turntables
were 10 seconds/turn, but that doesn't mean everybody uses that rotation
rate. And the "always run the motor an integer number of turns" is a
software feature that might not be in some controllers, though I've
noticed it in the ovens I've used.

My impression is that it continues to run while it is beeping. I can
tell when the magnetron turns off by running a radio on a fairly weak
station next to the oven. Which I do a lot of the time, because I
listen to two stations 50 miles from here.

You can usually tell that the magnetron is on by the humming from the
high-voltage transformer. Set the oven to 50% power, and you should
hear the transformer hum turn on and off with about a 50% duty cycle and
a period of perhaps 15 seconds.

Dave

On Jul 17, 1:00 am, (Dave Martindale) wrote:


Did you ever wonder why, if you select 45 seconds of heating, the
magnetron runs for 45 seconds but the motor continues to run for another
5 seconds after the magnetron is off? Because the turntable motor
always runs for an integer multiple of the turntable rotation period,
usually 10 seconds. So if you put something at the front of the
turntable, near the door, it will be in that position again when the
oven shuts off.

Dave

Ok, you got my interest up enough to try it. My Sharp turntable stops
when the timer reaches 0 no matter what it's rotational position.
Yours must be manufacturer specific.

Red