Can a PWM generated from the PIC microcontroller to control TRIAC? Need help. urgent

[Chee Hoe]

thank you guys. i understand that the capacitor inserted will help in improve the PF as well as the performance of the motor. by the way can i build the same circuit as given by this **broken link removed** website? is there any precaution steps need to be taken when building this circuitry?

 

[Chee Hoe]

thank you guys. i understand that the capacitor inserted will help in improve the PF as well as the performance of the motor. by the way can i build the same circuit as given by this **broken link removed** website? is there any precaution steps need to be taken when building this circuitry?

 

[MrAl]

I have used off the shelf light dimmers to run shaded pole motors on small fans and whatnot a number of times. The capacitor goes in parallel with the motor. What I have found is that many light dimmer circuits don't work smoothly on small induction motors so a little bit of capacitance to cancel out the motors inductance is necessary.

Hi again tcm,

Dont you feel that some series resistance is in order for that capacitor? After all, it will be driven with a fast rising wave front when the triac turns on. Worse case i guess is at 90 degree conduction angle (and 180+90 of course) where the triac will be turning on into a capacitor at 170v peak (for a 120vac line). It's almost like pulsing a capacitor directly with a one shot and MOSFET driver with a supply voltage of 170vdc...not something we want to do. Some series resistance would limit the peak current through the cap. Cap seems like good idea though.

 

[tcmtech]

I think you guys are way over analyzing the concept.

All the small capacitor does is correct the motors power factor to get it to appear more like a resistive load so the dimmers phase angle based firing circuit through the diac stays stable.

 

[Chee Hoe]

hmm... guys... can i build the same circuit as given by this **broken link removed** website for the AC speed control? is there any precaution steps need to be taken when building this circuitry?

and thank you for sharing for the opinions and knowledge... i learned a lot from it

 

[Chee Hoe]

tcm and mrAI, today i tried to build this circuit **broken link removed** however the speed of the motor doesnt change when i was adjusting the pot. the motor i'm using is just 38watt. please advice, need your help. tq

 

[Nigel Goodwin]

@tcm and mrAI, today i tried to build this circuit **broken link removed** however the speed of the motor doesnt change when i was adjusting the pot. the motor i'm using is just 38watt. please advice, need your help. tq

As has been advised right through this thread, you need to alter the FREQUENCY to change speed of this kind of motor. You might get some crude kind of change, but it's only because the motor isn't receiving enough power to run properly.

 

[Chee Hoe]

the DIac i used is DB3 and the triac model is Bt136-600D, this combination got problem ?

 

[Chee Hoe]

As has been advised right through this thread, you need to alter the FREQUENCY to change speed of this kind of motor. You might get some crude kind of change, but it's only because the motor isn't receiving enough power to run properly.

but before that tcm told me that this kind of motor can be ran by using dimmer circuit ?? hmm.. confuse.... so do you meant TCM said wrongly? the motor i'm using is just single phase ( Table Fan motor).

besides, the motor is now keep running in high speed, therefore i don't think it didnt receive enough power.

 

[tcmtech]

You never stated what type of motor it was exactly. There are many types of single phase motors and not all work the same way.

Small fractional HP motors are most often shaded pole types, but not always, and they can be controlled with most dimmer style circuits by basically limiting their power to control their speed.

The problem with DIY circuitry being used on an unknown motor type is its not so easy to work with as you are finding out. If your motor can be speed controlled by varying the input voltage supply to it with a variac without burning it up it most likely could be controlled with a dimmer circuit too but the circuit would have to be set up properly to work with it. Its not just a plug and play type operation to say the least.

If it cant be controlled by voltage adjustment then its not a shaded pole type and frequency changing is going to be your only option.

 

[JimAvanti]

here is a speed control using a 555, an opti couplier a triac and a zero crossing detector
https://www.electro-tech-online.com/custompdfs/2012/04/AN-3006.pdf

Hello, I am looking to control a small A/C fan in a similar way. I was hoping someone still had this .pdf file (The link no longer works).
Thanks,
Jim

 

[JimB]

Try this:
https://www.fairchildsemi.com/an/AN/AN-3006.pdf
I did a quick google for AN-3006 and this was the first hit.

JimB

 

[KeepItSimpleStupid]

Small AC motors CAN be controlled with Phase Angle Fired controls, but not the light dimmer variety. You have to hunt for the application notes out there.

With a resistive load, it's rather straightforward to control dimming. You have a table of phase angles and power relationships and you trigger the line at some time after a zero cross and your basically done. The lamp turns off when the voltage goes to zero.

With a motor, the voltage goes to zero at a different time than the current goes through zero, so you have to keep turning on the triac.

In a typical dimmer, the triac turns on at some voltage with a pulse and it stays on until it turns off.

So, you want to build one of these:

for your school project?