I want to control motor speed with capacitors

Thread Starter

mtalent

Joined Oct 2, 2017
30



above left is the circuit I want to build

I am going to use electronic switches controlled by a micro-controller. My question is about the capacitor values, I am having a bit of a time finding the ones indicated

I was able to find this ..... CBB61 Ceiling Fan Capacitor for NEW TECH 5 Wire 4.5 uf+5uf+6uf 250 VAC....



My question is will this work to control fan speed, how does the increase capacitor values change the results. Also would this part work with 110 because it says 250VAC

I would like to use the recommended values but I am having a hard time finding them if anyone has any ideas

thanks
 

crutschow

Joined Mar 14, 2008
24,101
If a small induction motor has a non-linear load, such as a fan, you can somewhat control the motor speed by reducing the motor voltage.
In that case the motor no longer has sufficient torque to maintain its speed and starts operating at a lower speed, with a large amount of slip between the synchronous speed and the actual speed.

But that doesn't work so well if the load has a more or less constant torque.
For that you need a Variable Frequency Drive (VFD) to change the speed.
 

Thread Starter

mtalent

Joined Oct 2, 2017
30
OK great,

Now let's say I try this one I have coming http://data:image/jpeg;base64,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

there are two grey wires on left and three (red, purple, brown) wires on right

I am trying to get in my mind why there are two grey wires and how exactly to hook to my switches

I will be working on it tonight, any help would be appreciated

Thanks

wayneh - very happy to hear that it will be here tommorow, also from what I am understanding a total of 4(from the one you showed) may not be enough for descent speed??

crutschow - from what I understand with the fan blades as the load this is supposed to work. I read one article that did indicate that without the fan blades this kind of setup does nothing for rpm
 

MaxHeadRoom

Joined Jul 18, 2013
19,730
It is a very poor way as the torque decreases drastically with reduced capacitance, also the rpm is never higher than applied frequency minus the slip.
Switched pole change winding's are better method.
The majority of ceiling fans are shaded pole, which can be controlled by Triac, also results in reduced torque.
Max.

upload_2017-10-2_22-19-48.png
 

GopherT

Joined Nov 23, 2012
8,012
It’s cheap and it works. Why would a consumer give a crap about anything else?
I'm a consumer and the buzz generated by the motor every time it skips over a pole is really an annoying sound so, as a former marketing person, I see an opportunity for a properly designed fan. Therefore, your argument that "cheap" is everyone's key buying factor is in question because your premise that a buzzing motor is considered to be a working motor is also in question.
 

wayneh

Joined Sep 9, 2010
16,162
Capacitor controlled fans are less likely to buzz. The speed control is not continuous though, and that’s probably their main disadvantage.
 

Alec_t

Joined Sep 17, 2013
10,723
Something to be aware of is avoiding resonance at the mains frequency or a multiple thereof. Resonance can result in very high voltages which stress insulation.
 

Thread Starter

mtalent

Joined Oct 2, 2017
30
Here is a link to a setup using an optocoupler and a triac and a micro-controller using pwm. It looks pretty interesting but it appears to be quit a bit more difficult. I bought an optocoupler and triac in case I wanted to try it. But, this setup with the capacitors looks way easier (I am a programmer not an electrical engineer).

https://www.nxp.com/docs/en/application-note/AN3471.pdf

Instead of the micro-controller they used I would use one of my rf200p81 wifi chips with pwm. I went through the setup and it mentioned a bridge that I am guess I would build but I was having a hard time understanding

4.2 Rectifier and Transformer
1. Identify the primary and secondary windings of the transformer (127 V - 60 Hz/ 6 V - 500 mA).
2. Connect common to GND. The GND must be common on the board
3. Connect the two cables of the secondary winding to the AC input on the bridge. Consult the
transformer data sheet to identify the cables.
4. Connect the positive side of the bridge to GND with a 10 K resistor.
5. Connect the negative side of the bridge to GND.
6. Check with an oscilloscope the voltage on the 10 K resistor. It must show the full wave rectified.

I think the capacitor setup should work fine.

Caps come in today

thanks for the help all

Mark
 

Thread Starter

mtalent

Joined Oct 2, 2017
30
Ok, I did what any good engineer would do. I went and got a 3 speed fan and took it apart.

It all looks pretty basic, I removed three screws to open the area containing the switch and caps.


then I pulled out the caps and removed the chain activated switch for a closer look.



and the actual switch



Ok one of the gray wires goes straight to the motor, the other runs through the switch and is in switch position one. the red which is the lowest uf of 4.5 goes straight to the motor. I believe this has to do with what someone on another sight said "The fan might not like being powered without any cap connected. Leave the low speed cap always connected, and switch two additional caps in circuit (four speeds possible).
If you also want on/off, then use a relay in series with the fuse.
Leo..
"

So now we have the purple (5uf in position 3) and brown (6uf in position 2) with the black (load) and one of the grays from the capacitor pack in the mechanical switch. Now my question --- Are we just increasing the total capacitor value with each switch (meaning that for setting 2 (medium) the switch for the brown is closed) and then for high we leave the switch on the brown closed and close the switch on the purple. So for low we have 4.5 uf, medium is 10.5 uf and high is 15.5 uf.

I am going to make a schematic of my electronic switch configuration so you guys can let me know if I am understanding this right. My schematic skills are not that great but I will try

thanks
Mark

Max and cmartinez I want to understand what you guys are talking about but it is tough for me. My understanding of the pwm is that you limit the duty cycle of the pin so it is turning on and off quickly and since it is off for an amount of time the amount of voltage getting to the motor is less. However, I have a feeling there is more to it than that. I'll post the picture of the whole circuit so maybe someone can help explain.

 

MaxHeadRoom

Joined Jul 18, 2013
19,730
What we were referring to is the method of using PWM to turn on a triac, which once triggered will stay on if the voltage is present, regardless if the input is pulsed, which makes PWM a little redundant.
IOW once the Triac is on, switching the gate on off has no effect until the zero crossing occurs.
See Fairchild AN-3006.
PWM is generally not used for AC motor control.
Max.
 

wayneh

Joined Sep 9, 2010
16,162
I am going to make a schematic of my electronic switch configuration so you guys can let me know if I am understanding this right.
I'm confused about what you are actually wanting to do. Your fan speed is already controlled by capacitors, as you have verified. Your post #14 seems to be branching into an entirely different direction and that's what Max and cmartinez responded to. I don't see any relevance to the current project.

Is your goal now to use a micro-controller to take the place of the mechanical switch, so that you can control the fan speed using the micro?
 
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