# AC single phase volt down fan

#### ricky diaz

Joined Feb 16, 2015
71
hi guys i have this easy task to complete, and this time i just need some advice to down the speed of a small 4 inches blower or fan, this is a 110 volt 2 speed fan and draws 0.44 Amps, i just need to step down that speed like say minus 30 volts, so i just tried with resistor in series for this task but nothing happens at all, so wich formula should i use to calculate the resistors or/and capacitors to achieve this task?, should be this in series or parallel?, thanks guys.

#### MikeML

Joined Oct 2, 2009
5,444
You cannot reduce the speed of an AC induction motor by reducing voltage. You would have to reduce the AC line frequency to slow the motor.

Joined Jul 18, 2013
26,270
Or if it is a shaded pole motor you may have luck with a Triac/dimmer style controller (ceiling fans etc).
Max.

#### ricky diaz

Joined Feb 16, 2015
71
You cannot reduce the speed of an AC induction motor by reducing voltage. You would have to reduce the AC line frequency to slow the motor.
Thanks Mike, you´re right, i never realice about frecuency, thanks again.

#### ricky diaz

Joined Feb 16, 2015
71
Well, known now about the real deal i wonder, how dificult is to make this circuit? i´ve allready have some mosfet on my spare and couple of 555 to make a PWM AC motor (small 110Volt .44 Amp fan) controller possible so i decided to get on the fight to learn something new, i know that a simple Dimmer will do the job but lets say i don want to waste money since now in my country we have a fucking inflation and is cheap to me make the circuit since i have all parts, do you guys now about any circuit in the forum for guiding? i´ve been looking but they all look high rate than my needings.

Joined Jul 18, 2013
26,270
I think you will be wasting you time looking at PWM for a induction motor, even a shaded pole motor, which most likely the fan is.
Max.

#### ricky diaz

Joined Feb 16, 2015
71
I think you will be wasting you time looking at PWM for a induction motor, even a shaded pole motor, which most likely the fan is.
Max.
Ok i´m starting realice some things, but what if i what to make any source power controled for lets say a power drill?, or vacum, or grinder? something like that, i just plug the cord into outlet previously done with the controled and i could make the speed of this tools more slow.

Joined Jul 18, 2013
26,270
That appears to be Triac Dimmer style controller, these will control shaded pole motors and Universal (series) motors used in power tools etc.
Max.

#### crutschow

Joined Mar 14, 2008
31,112
When I tried a light dimmer with my fan, it caused a noticeable buzzing sound in the motor so I instead used a series capacitor, which worked well.
You need several microfarads of capacitance (experiment to determine the desired value) and they must be a non-polarized film type with a maximum voltage rating greater than the peak mains voltage.
I used several 1μF audio crossover capacitors in parallel.

#### ricky diaz

Joined Feb 16, 2015
71
ok i understand that, but what if i want to do my own dimmer? what´s the dimmer anatomy? it is possible to make? those are my questions, what do i need to make a dimmer or so, cause as i tell you i have a bunch of retrievd parts that i can use, power mosfets, probbably some diacs, lot of resistance, caps, optocouplers, and so, my goal is to reuse the good parts and learn something new in the process, remember guys i´m a learner in this meaning. cheers.

Joined Jul 18, 2013
26,270
Max.

#### ricky diaz

Joined Feb 16, 2015
71
Ok Basically a Diac and Triac are diodes specifically designed for AC switching as far i can see, but what about schottky diode? just to mention, i know they are going out of use now, but i have some of very hugh current/volt capacity and i would like to use them if possible, is it recomendable for AC swtchin speed control? my question, probbably i´m missing something.

#### #12

Joined Nov 30, 2010
18,224
what about schottky diode? , i know they are going out of use now, i would like to use them if possible, is it recomendable for AC swtchin speed control? my question, probbably i´m missing something.
Uh...yeah. Trying not to ask you what you have been smoking...
Shottky diodes are just diodes that are more efficient than usual. The use of them is irrelevant to this circuit like asking how many trucks I should have in the church choir. Trucks can't sing and diodes are only switches in relation to the rest of the circuit. Not part of a dimmer as far as I know.

But I have a lot of trucks.
They still can't sing.