Fan motor capactitor use.

What is the difference between A/C (air conditioning) fan motors that use a start capacitor and say a ceiling fan that doesn't. Type slow because I'm not too bright and getting worse...
--
Tekkie

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Tekkie® wrote:

Interesting question. I'm not an expert on this, but I knew just enough to type out an answer. I was on the right track ( %-)), but someone explained it better at the link below (so I deleted what I wrote)! HTH!
https://itstillruns.com/ac-motor-need-capacitor-start-6596783.html
Bill
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On Thursday, July 26, 2018 at 3:48:43 PM UTC-4, Tekkie® wrote:

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What makes you sure that it doesn't? Just because it's not separate and visible, doesn't mean there isn't one inside.
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On 7/26/18 3:48 PM, Tekkie® wrote:

Resistance to startup- i.e., overcoming inertia- is the issue.
High in an AC compressor (needs a boost from a capacitor) but low in a ceiling fan (no capacitor necessary).
Think of it like a morning coffee-jolt...
--
The fastest way to stop a bad guy with a gun is a good guy with a gun.

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On Thursday, July 26, 2018 at 6:56:03 PM UTC-4, Wade Garrett wrote:

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AFAIK, they are both AC induction motors and you need a phase shift, generated somehow, to get them moving.
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wrote:

We finally get to say "split phase" and be correct. The capacitor actually does "split" the single phase in conjunction with the start winding in the motor and it creates a temporary "2 phase" system for a second until the motor gets out of locked rotor.
Smaller motors may be "shaded pole" that create a magnetic shift in the motor windings themselves without a capacitor. Usually, if you look you will see a much larger gauge winding there, maybe only one or 2 turns. That creates the shaded pole. They are not particularly efficient and they have very low starting torque but if it is a $12 fan from Walmart, what do you expect? The other place you see shaded pole motors is in small gear head motors like you might see on a refrigerator defrost timer. Since the gear reduction is so great and the load so low, they don't need much torque.
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On Thursday, July 26, 2018 at 7:57:46 PM UTC-4, snipped-for-privacy@aol.com wrote:

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The question remains which of those is in most ceiling fans and does it use a cap? Looks to me like most are split-phase, in which case they use a cap and are in the same category as the AC motor.
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On Thu, 26 Jul 2018 17:15:06 -0700 (PDT), trader_4

A ceiling fan is usually a split phase motor with a start capacitor but it is not a very big capacitor since they don't need a lot of torque. The cheapest ones might even have a shaded pole motor and a top of the line model may have a brushless DC motor.
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snipped-for-privacy@aol.com posted for all of us...

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I never knew they had capacitors in them. Of course I didn't do a through exam of any on a ladder or destruction. I always assumed they were shaded pole motors.
Leads to the next question: How do they perform different speeds?
--
Tekkie

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wrote:

They just drop the field voltage and allow the rotor to slip. That is why some of them "moan". As I said some high end fans now use brush less DC motors and pulse width controllers.
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On Friday, July 27, 2018 at 5:45:39 PM UTC-4, snipped-for-privacy@aol.com wrote:

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I thought they had different windings with different numbers of poles in there, using different number of poles to get a 3 speeds.
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On Fri, 27 Jul 2018 16:12:17 -0700 (PDT), trader_4

I suppose some do but they also have dimmer style controls that just vary the voltage. The little plastic desk and pedestal fans do have multiple windings as far as I know. Larger fans like air handler blowers do use multiple windings.
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On 07/27/2018 06:49 PM, snipped-for-privacy@aol.com wrote:
[snip]

Varying the voltage is possible, but would be very wasteful. Dimmer controls vary duty cycle.

I know about a the 3-speed (inside fan) motor in the A/C where I used to live. It has 4 wires, common and one for each speed.
Here, I have a 3-speed ceiling fan control that has only 2 wires.
--
Mark Lloyd
http://notstupid.us/
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