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Perhaps a dumb electronics question
Posted by: PeterB
Date: November 20, 2021 09:42AM
I think I already know the answer to this, but... I'm sure some here are more electronically-inclined than me.

If you have a motor that appears to only turn in one direction, is there any way to get it to go the other direction? Is it just a matter of reversing polarity?

I'm asking because I have a portable ceiling fan that, sadly, seemingly only turns one way. It's long out of warranty, so I'm tempted to add a switch (if it's possible to do it that way) to make it reversible. It's a great fan, other than the inability to reverse. (My understanding is that, in winter months, it's better to have the fan turning in a direction to create an updraft...) The only other way I can think to do it is to reverse the blades' sides, but I'm not sure that'd be possible with this fan.

TiA




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Re: Perhaps a dumb electronics question
Posted by: davester
Date: November 20, 2021 10:01AM
First of all, this is an electrical question, not an electronics question.

Second, a ceiling fan is powered by alternating current electricity, so there is no polarity to be reversed and switching the two power leads will not reverse the motor.

Third, the method of controlling rotation direction of a motor depends on the type of motor, the number of phases it has, or how the starter circuit is wired.

It is unusual for a ceiling fan to not be reversible. However, it could be that it's either a low end fan or perhaps the controller is not wired correctly or missing. Does it have a wall controller? Could be that the original controller broke and the prior owner substituted a simple switch.



"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion." (1987) -- Carl Sagan



Edited 1 time(s). Last edit at 11/20/2021 10:02AM by davester.
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Re: Perhaps a dumb electronics question
Posted by: testcase
Date: November 20, 2021 10:14AM
What davester said. boink smiley
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Re: Perhaps a dumb electronics question
Posted by: PeterW
Date: November 20, 2021 10:39AM
Wtf is a “portable ceiling fan”?
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Re: Perhaps a dumb electronics question
Posted by: Cary
Date: November 20, 2021 10:41AM
Are you sure there isn't a small switch on the body of the fan for reversing direction?
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Re: Perhaps a dumb electronics question
Posted by: space-time
Date: November 20, 2021 10:43AM
Quote
PeterW
Wtf is a “portable ceiling fan”?

Maybe he is camping?



Edited 1 time(s). Last edit at 11/20/2021 10:43AM by space-time.
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Re: Perhaps a dumb electronics question
Posted by: space-time
Date: November 20, 2021 10:45AM
I think I already know the answer to this, but...

What was your best guess?
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Re: Perhaps a dumb electronics question
Posted by: PeterB
Date: November 20, 2021 10:45AM
Quote
davester
First of all, this is an electrical question, not an electronics question.

Second, a ceiling fan is powered by alternating current electricity, so there is no polarity to be reversed and switching the two power leads will not reverse the motor.

Third, the method of controlling rotation direction of a motor depends on the type of motor, the number of phases it has, or how the starter circuit is wired.

It is unusual for a ceiling fan to not be reversible. However, it could be that it's either a low end fan or perhaps the controller is not wired correctly or missing. Does it have a wall controller? Could be that the original controller broke and the prior owner substituted a simple switch.

1) Well, I considered it to be an electronics question too, since I thought it might be a matter of adding a switch.

2) I'm presuming the fan has a DC motor, since it is a portable (not hardwired) fan, and that there might be a transformer in there somewhere.

3) Understood about how to control rotation.

4) Again, it's not a problem with a controller, it is/was designed this way. Simple plug in with on/off switch. It has nothing to do with damage or a previous owner. Edit: Cary, no, there is no reversal switch on this fan. It's the type of fan that's designed for an RV or porch, for a situation where you don't necessarily want to hardwire something.




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Edited 1 time(s). Last edit at 11/20/2021 10:47AM by PeterB.
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Re: Perhaps a dumb electronics question
Posted by: davester
Date: November 20, 2021 10:48AM
Ah, I didn't notice the word "portable", just the word "ceiling". I'm not even sure how a ceiling fan can be portable.



"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion." (1987) -- Carl Sagan
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Re: Perhaps a dumb electronics question
Posted by: PeterB
Date: November 20, 2021 10:58AM
Quote
davester
Ah, I didn't notice the word "portable", just the word "ceiling". I'm not even sure how a ceiling fan can be portable.

I don't know if they sell the exact model I have any more, but here's essentially the same thing: [www.amazon.com]
(the reviews aren't great, but I've actually found it to work pretty darned well, in terms of airflow)




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)
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Re: Perhaps a dumb electronics question
Posted by: Bernie
Date: November 20, 2021 11:17AM
What is Shaded Pole Motor?

Definition: A shaded pole induction motor is a simple single-phase induction motor, which is self-starting with one of the poles shaded by the copper ring. The other name of the copper ring is a shaded ring, where it acts as a secondary winding motor. It rotates only in one direction particularly and reverses moment is impossible. This motor has very high power induction losses and also has a very low power factor. Starting torque induced in the motor is very low. Due to these reasons, it has poor efficiency. This, it has low power ratings. It is also a salient pole split phase motor.

Great for fans though




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Re: Perhaps a dumb electronics question
Posted by: Ombligo
Date: November 20, 2021 11:58AM
hang it upside down or put it on a pole stand pointed up.



“No persons are more frequently wrong, than those who will not admit they are wrong.” -- François de La Rochefoucauld

"Those who cannot accept the past are condemned to revise it." -- Geo. Mathias
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Re: Perhaps a dumb electronics question
Posted by: MrNoBody
Date: November 20, 2021 12:11PM
Second, a ceiling fan is powered by alternating current electricity...

No longer true. Modern ceiling fans are sometimes brushless DC motors.
Inside their housing or control box is a TRIAC/DIAC module. It converts
the line AC to DC and permits polarity reversing & speed control.
The low current motor doesn't even require a heat sink for the module.

A bigger version is used in multi-speed floor polishers which do need
a heat sink as they draw 15-20A.

simple schematic:


low power TRIAC:




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Edited 1 time(s). Last edit at 11/20/2021 12:18PM by MrNoBody.
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Re: Perhaps a dumb electronics question
Posted by: PeterB
Date: November 20, 2021 01:33PM
Quote
Ombligo
hang it upside down or put it on a pole stand pointed up.

Y'know, that's actually not a bad idea. Since I have to clean the fan blades anyway, I was figuring that I'd probably have to take it down to install a switch (if it were possible to do that)... but flipping it, if I can get it to stand upright somehow, would certainly be an easier solution... thanks!

Of course, a remote with reverse and speed controls would be nice... I see they offer that on some other models.




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Re: Perhaps a dumb electronics question
Posted by: Cary
Date: November 21, 2021 09:21AM
Did not know there was such a thing - thanks for sharing.

I would be cautious mounting upside down - I imagine the bearing design is for weight to be carried in designed direction. Who knows - I may be completely wrong...
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Re: Perhaps a dumb electronics question
Posted by: PeterB
Date: November 21, 2021 11:22AM
Quote
Cary
Did not know there was such a thing - thanks for sharing.

I would be cautious mounting upside down - I imagine the bearing design is for weight to be carried in designed direction. Who knows - I may be completely wrong...

It's a handy item for people living in an RV or an apartment, where permanent installation of a ceiling fan is impractical or impossible, or like in my situation, where I own, but don't want to deal with the full blown install of a permanent fan.

And frankly it was cheap enough that if it eventually dies, it's not the end of the world; and because it's not a permanent install, it'd be easy enough to toss it.

I see there are versions of these that ARE reversible and furthermore, have remote controls ... so when this one dies, I might replace with one of those.




Freya says, 'Hello from NOLA, baby!' (Laissez bon temps rouler!)



Edited 1 time(s). Last edit at 11/21/2021 11:22AM by PeterB.
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