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Subject Author Date
Fan motor runs backwards Bobo 07-13-2007
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Posted by Mike Dobony on July 13, 2007, 9:24 pm

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



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Posted by mm on July 13, 2007, 11:20 pm
On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"

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


Posted by Mike Dobony on July 14, 2007, 2:00 am

> On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
>
>>
>>> On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
>>>
>>>>
>>>>>
>>>>>> 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.
>



Posted by on July 14, 2007, 9:14 am
>
>
>
>
> > On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
>
> >>> On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
>
>
> >>>>>> 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.


Posted by Butzmark on July 14, 2007, 10:16 am
On Sat, 14 Jul 2007 06:14:24 -0700, pheeh.zero@gmail.com wrote:

>>
>>
>>
>>
>> > On Fri, 13 Jul 2007 20:24:43 -0500, "Mike Dobony"
>>
>> >>> On Fri, 13 Jul 2007 23:38:13 GMT, "Mike Dobony"
>>
>>
>> >>>>>> 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.


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