Design of 3 speed electric motor

[nitin3011]

We are making electric fans of 100 W capacity with speed of 1400 rpm
now i wan to make this fan in 3 speed with speeds of about 1200 rpm,1300 rpm and full speed of 1400 rpm. Can somebody pls help in designing the winding data or let me know how to design the winding data. Any empirical formulae or tip would be of immense help

 

[GreenGiant]

First off, the difference in 1200 - 1400RPM would not be very significant

That aside, you should be able to use a 1400 RPM rated fan and then just use a PWM or voltage control (depending on type of fan) circuit to change the speed with a potentiometer

 

[nitin3011]

Sir
i want to do the same by making a tap on the windings. after that we can place a selector switch the motor so that user can do the same himself without any problem.
Pwm etc. is not possible in small cheaper fans.

 

[GreenGiant]

Sir
i want to do the same by making a tap on the windings. after that we can place a selector switch the motor so that user can do the same himself without any problem.
Pwm etc. is not possible in small cheaper fans.

PWM is possible almost anywhere a DC motor is used, and voltage regulation can be used almost anywhere (DC or AC)

Working with the windings (unless there are very few) it will be hard to pinpoint the spot that would give you set RPM's, plus usually there are multiple layers, unless you want to unwind and rewind the motor you will get very limited speed variance, plus you risk crossing some wires, or breaking connections, while introducing a small control system between the power input to the coils you can achieve different speeds

 

[Eagleye]

PWM is possible almost anywhere a DC motor is used, and voltage regulation can be used almost anywhere (DC or AC)

Working with the windings (unless there are very few) it will be hard to pinpoint the spot that would give you set RPM's, plus usually there are multiple layers, unless you want to unwind and rewind the motor you will get very limited speed variance, plus you risk crossing some wires, or breaking connections, while introducing a small control system between the power input to the coils you can achieve different speeds

Instead of controlling voltage by tapping into winding if any light dimmer type circuit is used, in that case how effective that would be?

The dimmer varies the effective voltage by chopping the waveform with a triac.

 

[john monks]

This is a rather straight forward problem but involves some work. First you need to count the number of turns you currently have. Next you will need a variac to turn the voltage down until the fan's speed by the necessary amount. Then you will need to add turns to the windings to make for that voltage drop. If the number of turns is 300 and you drop the voltage by 50 percent to get half the speed you will have to add 300 more turns making 600 turns. So there you have the ratio. This is assuming you have an induction motor and that the wire resistance is negligible. The reason for the test is to find out how much the voltage variance affects the speed. This is a complex equation because now you are concerned with aerodynamics.