Calculating the value of the resistance for controlling the speed of AC fan

[sino007]

i have a single phase ac fan that i would like to control its speed i am a bit new in this field so please bear with me

i had the idea of fixing 3 speeds with 3 switches one for each speed: (25% 50% 90%), and 3 relays each switch activates a relay and each relay wired in series with a resistance of a certain value so we have 3 speeds for every resistance (see the attached image)

i dont know the type of the motor (synchronous , asynchronus ,wound rotor...)

the motor have the following informations: 220 v , 50 Hz , 39W

i didnt make any mesurements (voltage,current..) when the fan is on

my question is am i on the right path for controlling my fan with 3 speeds ?is there a better way ? how to determin the value of the 3 resistances if i want to fix the following speeds (25% 50% 90%)

thank you

 

[Cicero]

No, for an AC fan with 3 settings, you dont want to just switch in resistors like that. Its inefficient and they will get hot etc etc.

Its generally done by switching in caps (with a high value parallel bleed resistor for safety), take a read through this http://wiki.diyfaq.org.uk/index.php?title=Fan_Speed_Controller

EDIT: Why is this thread in Automotive Electronics?

 

[sino007]

thank you cicero for your reply
i am new at this forum what thread do you suggest

 

[Cicero]

thank you cicero for your reply
i am new at this forum what thread do you suggest

I'd have just put it into General Electronics Chat. But never mind, one of the mods could move it for you if they want to.