[SOLVED] Motor control by varying voltage instead of PWM

[mitz]

I am planning to make an Arduino - IR & proximity based voltage controller for AC 60W fan which has few air flow modes. Instead of PWM which makes noise, I think of using ST13005A power transistor. Is is correct to control the fan speed by varying the voltage? How abt the motor's life in this case? Would you plz suggest?

 

[shaiko]

You can do that. The downside of this approach is that motors generally operate better (more efficiently) near their nominal voltage. With voltage control you operate off-nominal most of the time.
Also, if you want to be able to turn your motor in 2 directions - it can be achieved much easily with PWM control and transistors.

 

[mitz]

How to eliminate the noise from the motor due to PWM?

 

[crutschow]

If you have the PWM frequency above 20kHz there shouldn't be any audible noise.

 

[mitz]

@ Zapper. Thank you for the good suggestion. At 6khz and below there was pwm noise but not able to increase speed from a minimum level even with 30khz.

 

[mitz]

Looks like the TIP 102 transistor is not able to switch high frequency.

 

[FvM]

The discussion is rather vague without a circuit. Everyone might have his own idea what's exactly meaned with motor PWM control. Linear voltage control with ST13005A isn't much clearer at first sight. The motor must be supplied with a pure AC voltage, in most cases, we would need at least two transistors to generate it.

 

[kripacharya]

for AC 60W fan which has few air flow modes ?

it's not clear exactly which type of fan is this. 'AC' seems to imply its operated from mains AC @ 220v or 110V depending on where you live.
Is this a ceiling fan ? Single phase ? In which case it is probably a single phase split-phase induction motor. This will respond to variations in the AC voltage (thats how conventional regulatros work) and also to scr/ triac controlled duty cycle variations of the 50//60Hz appliad AC.

How this will respond to a 30khz PWM would be interesting to learn.

Also - can you explain what you mean by 'few air flow modes' ?

 

[mitz]

The fan is AC single phase 220v, 60W exhaust type. Air flow modes are to simulate different winds like breeze, sea breeze etc.

After discussing here, I tried pwm using TIP 102 in a 12v brush type dc motor running a table fan. Vcc given to motor and the other wire of motor to TIP 102's collector.

The main requirement is the silent operation of the fan as done through fixed regulator. MCU controls the TIP 102 to generate different speed in this setup. In the AC fan another suitable one ST13005A is thought to be used. Pls say your suggestion.

 

[crutschow]

If you can tolerate discrete steps of speed then you could use a capacitor in series to efficiently and silently reduce the AC voltage. You could select different banks of capacitors to vary the speed in steps (sequentially connect them in parallel). You would have to experimentally determine the capacitor size for the desired speeds. I used a few microfarad with a large room fan to reduce its speed.

Note that the capacitor must be a non-polarized (film) capacitor with a voltage rating of at least 400V. I used some designed for speaker crossovers.

 

[mitz]

@ Zapper : Thank you very much. I am too having similar thought but the life of these capacitors seems short as they fail in an year or two with those found in ceiling fan regulators.