Ceiling Fan Speed Control:
- Thread starter rattus
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electricmanscott
Senior Member
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- Boston, MA
Re: Ceiling Fan Speed Control:
The basics are pretty much hi, medium and low.
Seriously what do you mean?
The basics are pretty much hi, medium and low.
Seriously what do you mean?Re: Ceiling Fan Speed Control:
In other words, I am asking for a verbal schematic diagram. It is not hard, but I think most electricians and engineers too have not been exposed to this problem and would benefit from a discussion of the pitfalls.
Scott, I asking for a bit more detail on the speed control wiring. Capacitive reactance is used, and the switch sequence may be a bit more complex than that of a simple 4-position pull chain switch.Originally posted by electricmanscott:
The basics are pretty much hi, medium and low.
In other words, I am asking for a verbal schematic diagram. It is not hard, but I think most electricians and engineers too have not been exposed to this problem and would benefit from a discussion of the pitfalls.
Re: Ceiling Fan Speed Control:
Yep Sam,
A recent thread discussed the effects of undervoltage on induction motors. Iwire opined that with fans, this is not the problem that it is with constant torque applications. In a nutshell, you can control fan speed by dropping the applied voltage.
Some ancient fans did this with series inductance; modern fans do it with series capacitance and sometimes with a dimmer made especially for inductive loads.
In a typical fan, the series cap value might be:
Hi speed: No cap
Med speed: 10uF
Lo speed: 5uF
Now Sam, tell me the switching arrangement which will provide this control with two 5uF caps.
Yep Sam,
A recent thread discussed the effects of undervoltage on induction motors. Iwire opined that with fans, this is not the problem that it is with constant torque applications. In a nutshell, you can control fan speed by dropping the applied voltage.
Some ancient fans did this with series inductance; modern fans do it with series capacitance and sometimes with a dimmer made especially for inductive loads.
In a typical fan, the series cap value might be:
Hi speed: No cap
Med speed: 10uF
Lo speed: 5uF
Now Sam, tell me the switching arrangement which will provide this control with two 5uF caps.
Re: Ceiling Fan Speed Control:
Sam,
Give me the part number for the switch, or better still, give me the switch sequence for the 4-position, pull-chain switch and tell me how to wire in the two caps.
Occasionally, one may be asked to repair one of these things, and one can waste a lot of time as I did doing it wrong.
Sam,
Give me the part number for the switch, or better still, give me the switch sequence for the 4-position, pull-chain switch and tell me how to wire in the two caps.
Occasionally, one may be asked to repair one of these things, and one can waste a lot of time as I did doing it wrong.
physis
Senior Member
Re: Ceiling Fan Speed Control:
Ok, I thought it was a test. I'll get back to you in a bit with it.
Mean while check out this equation and see if it relates to the speed control. Yes, I did do the longhand version just to be a wise guy.
I spent like an hour trying to convince my software to make this nice and pretty but nothin' doin'. I finally realized there's a scanner right here, what am I arguing with Bill Gates products for. It's strange that writing this equation can be a huge challenge to technology.
Ok, I thought it was a test. I'll get back to you in a bit with it.
Mean while check out this equation and see if it relates to the speed control. Yes, I did do the longhand version just to be a wise guy.
I spent like an hour trying to convince my software to make this nice and pretty but nothin' doin'. I finally realized there's a scanner right here, what am I arguing with Bill Gates products for. It's strange that writing this equation can be a huge challenge to technology.
physis
Senior Member
Re: Ceiling Fan Speed Control:
The reason I put the equation up is because you can consider the motor to be a resistance and an inductance in series, and by putting a capacitance in series with the motor you have an RCL series circuit.
It's impedance is given by the formula.
The point is that you aren't lowering the voltage, you're lowering the current, by raising the circuit's impedance.
Here's the schematic you want.
The reason I put the equation up is because you can consider the motor to be a resistance and an inductance in series, and by putting a capacitance in series with the motor you have an RCL series circuit.
It's impedance is given by the formula.
The point is that you aren't lowering the voltage, you're lowering the current, by raising the circuit's impedance.
Here's the schematic you want.
Re: Ceiling Fan Speed Control:
Sam,
You are getting warm but no cigar, not even a cigarillo. If you lower the current, you have also lowered the voltage.
Your schematic provides 0, 5, and 2.5uF for the three speeds, but we must have 0, 10, and 5uF. It is a little trickier than you thought.
Give up?
Sam,
You are getting warm but no cigar, not even a cigarillo. If you lower the current, you have also lowered the voltage.
Your schematic provides 0, 5, and 2.5uF for the three speeds, but we must have 0, 10, and 5uF. It is a little trickier than you thought.
Give up?
physis
Senior Member
Re: Ceiling Fan Speed Control:
Oh quit.
If you parallel those capacitors you'll need a two pole switch. You can do it with SP so it would be a waste. The capacitance is selected for an SP switch because capacitors are very inexpensive comparitively and they're also the same value because that's how you get a quantity break. If you check the RPM you'll find that you can get better symmetry with different capacitances.
Give up.
Oh quit.
If you parallel those capacitors you'll need a two pole switch. You can do it with SP so it would be a waste. The capacitance is selected for an SP switch because capacitors are very inexpensive comparitively and they're also the same value because that's how you get a quantity break. If you check the RPM you'll find that you can get better symmetry with different capacitances.
Give up.
Re: Ceiling Fan Speed Control:
Rattus I have replaced several of these switches and never once notice they used series capacitance to limit the current.Is that what that little square black thingy is a cap?
Now that you mentioned it, it would make a very simple control to just limit the avalible current to the motor winding with a series cap.
When I change one out I take one wire out at a time and put that wire on the new switch untill I have chnged them all.
Ps you don't have to respond.
Rattus I have replaced several of these switches and never once notice they used series capacitance to limit the current.Is that what that little square black thingy is a cap?
Now that you mentioned it, it would make a very simple control to just limit the avalible current to the motor winding with a series cap.
When I change one out I take one wire out at a time and put that wire on the new switch untill I have chnged them all.
Ps you don't have to respond.
Re: Ceiling Fan Speed Control:
Ronald, indeed that little black thing is a cap, probably two. And, your method is correct, but the point that I am trying to make is that the replacement switch which looks like the old one may be different.
For example, the switch I just replaced has a second layer which provides a switch pattern as follows:
OFF
Hi: L-1
Med: L-2, L-3
Lo: L-3
Now connect 5uF caps between pins 1 & 2 and connect another between pins 2 & 3.
Connect pin 1 to the motor and connect L to the hot wire.
Sam, dope this out and you will obtain the desired capacitances.
And too, if we don't drop the motor voltage, it won't know to slow down!
Ronald, indeed that little black thing is a cap, probably two. And, your method is correct, but the point that I am trying to make is that the replacement switch which looks like the old one may be different.
For example, the switch I just replaced has a second layer which provides a switch pattern as follows:
OFF
Hi: L-1
Med: L-2, L-3
Lo: L-3
Now connect 5uF caps between pins 1 & 2 and connect another between pins 2 & 3.
Connect pin 1 to the motor and connect L to the hot wire.
Sam, dope this out and you will obtain the desired capacitances.
And too, if we don't drop the motor voltage, it won't know to slow down!
physis
Senior Member
Re: Ceiling Fan Speed Control:
That would indeed work and also jive with your numbers Rattus.
It's odd though.
Most switches I've dealt with with that kind of make pattern have been in the 20mA. range.
Alright, I might have to let you off the hook on this one. But I'm still not completely convinced you didn't backwards engineer it wrong.
That would indeed work and also jive with your numbers Rattus.
It's odd though.
Most switches I've dealt with with that kind of make pattern have been in the 20mA. range.
Alright, I might have to let you off the hook on this one. But I'm still not completely convinced you didn't backwards engineer it wrong.
Re: Ceiling Fan Speed Control:
Sam, your first diagram is schematically correct but it is not a wafer switch. It is a two layer pull chain switch which provides the desired switch sequence. I assure you that this is correct. I scratched my head for an hour until I realized that the two gray wires from the cap were common.
Your second diagram would work if the caps were 10uFd each, but this makes it less attractive. A 5 and a 10uF would have been a better choice. Two 5uF caps are even better although the switch costs a few pennies more. It is all about cost as you know.
Sam, your first diagram is schematically correct but it is not a wafer switch. It is a two layer pull chain switch which provides the desired switch sequence. I assure you that this is correct. I scratched my head for an hour until I realized that the two gray wires from the cap were common.
Your second diagram would work if the caps were 10uFd each, but this makes it less attractive. A 5 and a 10uF would have been a better choice. Two 5uF caps are even better although the switch costs a few pennies more. It is all about cost as you know.
physis
Senior Member
Re: Ceiling Fan Speed Control:
Try these arbitrary values:
Motor inductance = 700 mH.
Motor Resistance = 100 Ω
Source Voltage = 120 V.
Capacitances:
0 uf
2.5 uf
5 uf
10 uf
The currents and voltage drops are interesing.
Check out what happens at 0 uf and 5 uf.
And look at the voltage drop across the motor with 10 uf and compare the current to 0 uf.
Try these arbitrary values:
Motor inductance = 700 mH.
Motor Resistance = 100 Ω
Source Voltage = 120 V.
Capacitances:
0 uf
2.5 uf
5 uf
10 uf
The currents and voltage drops are interesing.
Check out what happens at 0 uf and 5 uf.
And look at the voltage drop across the motor with 10 uf and compare the current to 0 uf.
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