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How can I slow down this fan?

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hkBattousai

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Hello guys,

I have trouble with my kitchen fan. It runs too fast and makes a lot of noise. I want to slow it down, but I'm not sure how can it be done.

I can figure out that the capacitor value should be reduced, but I don't know how to compute the new capacitor value since this is not an ordinary R-L-C circuit.

These are the pictures of my fan:
**broken link removed** **broken link removed**

And this is the block diagram of the circuit:
**broken link removed**

Any help will be appreciated.
 
The capacitor isn't connected to ground. It should be between one of the motor connections and live or neutral.

The capacitor is for starting the fan. If you reduce it, the fan with either run at the same speed or not at all.

You might be able to reduce the speed with a resistor in series with the motor, but that sort of motor is really designed to run at one speed.
 
The capacitor isn't connected to ground. It should be between one of the motor connections and live or neutral.

The capacitor is for starting the fan. If you reduce it, the fan with either run at the same speed or not at all.

You might be able to reduce the speed with a resistor in series with the motor, but that sort of motor is really designed to run at one speed.

I'm quite positive that one end of the capacitor is connected to the ground. The power is connected to the fan through the pins F3 and F4. And the capacitor is connected through F1 and F2. I don't know the connections which are inside the fan. I have few knowledge about electric motors.
 
Unless the mains cable colours are completely different from what is used in the UK, the capacitor isn't connected to ground. If the capacitor did connect to ground, the fan would trip an earth leakage circuit breaker.

Green/yellow is normally ground. Green/yellow in the mains supply cable connects to green/yellow in the motor cable, which probably earths the motor case. It doesn't carry any current in normal use.

Brown is normally live. That connects to the black wire on the motor and to one side of the capacitor, a white wire. The other side of the capacitor, also a white wire connects to the brown wire on the motor. The blue wire, which is normally neutral connects to the motor.

Anyhow, that is how I understand your photo. The motor is a capacitor run induction motor.
 
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I've used a triac lamp dimmer to slow a fan but it caused buzzing in the motor. So I used a non-polarized cap in series with the fan motor which efficiently and quietly slows in down. The value needed may have to experimentally determined but it's probably in the neighborhood of a few microfarads. You could buy several 1µF caps and then sequentially connect them in parallel until you get the speed you want. You could also use a switch to control the number in parallel to change the speed.

The caps should be at least 400V non-polarized such as used in audio crossover networks or a motor run capacitor such as already used in your motor.
 
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I've used a triac lamp dimmer to slow a fan but it caused buzzing in the motor. So I used a non-polarized cap in series with the fan motor which efficiently and quietly slows in down. The value needed may have to experimentally determined but it's probably in the neighborhood of a few microfarads. You could buy several 1µF caps and then sequentially connect them in parallel until you get the speed you want. You could also use a switch to control the number in parallel to change the speed.

The caps should be at least 400V non-polarized such as used in audio crossover networks or a motor run capacitor such as already used in your motor.

I have thought connecting a series capacitor as well, but how do I prevent accidentally falling into the series resonance region?
 
I have thought connecting a series capacitor as well, but how do I prevent accidentally falling into the series resonance region?
With the low frequency of the power line, it's unlikely that you will be close to any resonant point of the capacitor and the motor inductance.
 
About Resonant frequency, isn't there enough resistance (internal resistance of fan and wires' resistance) to make Resonant frequency insignificant?
 
With the low frequency of the power line, it's unlikely that you will be close to any resonant point of the capacitor and the motor inductance.

I don't know much about electric machines, is there any method to calculate effective inductance of a motor in terms of inductance of its internal windings, rotational speed, and number of poles? I've always wondered this.
 
Pricipially this Motor is a 3 Phase Current Motor.
2 Pins are conected to Power Supply, one Phase is connected via a capacitor to Phase or Neutal. That generates a phase shifting.

When the 3 Coils inside the Motor are similar, the speed can be controlled with an frequency inverter.

Most times the Coils are different and it wouldn't work right.

The colours looks like in Germany. Black is Phase, Blue is Neutral, Green / Yellow is conected to Box and protection ground.
 
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