Problem in AC fan speed control(using ZCD and Atmega8A) when running on Inverter

Go To Last Post
19 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I recently built an AC fan speed control circuit using Atmega8a using Triac and ZCD method.I am attaching the necessary circuit regarding the triac firing and ZCD.The Atmega is configured to drive the MC3021 on falling edge detection.Please take a look.The fan speed is controlled in 5 different steps(namely-0,1,2,3,4).In 0,the micro is switching off the MOC3021 completely so the output is 0.Also in '4',the output of the micro is continuously giving '1',so that the MOC3021 stays on and the fan rotates in full speed.The speed control is done in 1,2 & 3.The speed control works perfectly on pure sine wave AC.But whenever electricity goes off and Inverter power takes place,the speed control malfunctions(Either the fan stops or it generates great hum and rotates very slowly).I saw with a DSO that the inverter is giving nearly square wave output.My question is,is this normal for the circuit to malfunction in square wave(zero cross is happening in square wave also so why is it malfunctioning??)or I am missing something??There is also external snubber attached using 39R and .01uF.In addition,when the circuit gives 0 to MC3021 i.e all off(while running on inverter),the square wave output of the inverter is stable.But whenever the circuit tries to control speed in either1/2/3,the square wave of the inverter gets distorted.The triac i used is BTA16.

 

Any hep is appreciated.Please reply soon.

Last Edited: Wed. Jun 1, 2016 - 09:04 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

How well does your fan run on the inverter without the speed control?  Perhaps its a fan problem and not the controller. 

 

 

 

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Fan runs as expected in full speed while on inverter.I don't think its a problem regarding the fan....

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Fan runs as expected in full speed while on inverter.I don't think its a problem regarding the fan....

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

There is a reason why 'full sine wave' inverters are more expensive than simple square wave inverters.
Guess what you need?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Is there anything that can be done to make the circuit working for those square wave type Inverters also??And one more thing i would like to add that the circuit works on the Inverter output only on Midnight or later.....How is this even possible??

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Rather than a triac, use a mosfet and a diode bridge. You need some means of generating the gate voltage - maybe a photomos device.
Why does it work after midnight? Black magic? Or something more down to earth like temperature or voltage? How do we know? We have no idea of what the setup is do we? What fan? What inverter? What supply? That's three what's - you're pretty dim!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Is the inverter providing a square wave or a "modified" sine wave.

 

See:

https://austinlightguy.wordpress...

 

If the inverter output is a modified sine wave, there is a limited region of valid turn on times available.

David (aka frog_jr)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The inverter is providing pure square wave.Screenshot attached.But whenever i am turning on the fan,the waveforms are getting crazy.This was taken while the fan was off.

 

Also this is the signal waveform taken at INT1 pin when a external fan (not controlled by the circuit) was running at full speed.All the things were powered by the Inverter.

 

 

But if i turn off the fan and then take the waveform at INT1(Also running in inverter),then it looks normal as on Pure AC.This next waveform was taken at INT1 pin while on pure AC.

 

 

 

Last Edited: Wed. Jun 1, 2016 - 08:49 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

What do the input and output signals of the optocoupler look like when running on the inverter?

David (aka frog_jr)

Last Edited: Wed. Jun 1, 2016 - 09:07 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Also when the fan is on(Running on inverter),the interval between the zero cross at INT1 pin is not symmetric i.e it is happening randomly.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

It appears that the square wave is crossing zero so quickly that the optocoupler does not have a chance to turn full off, thus the interrupt is not being triggered as it should...

David (aka frog_jr)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

But it is only happening when the fan is running.I saw that whenever the fan is off,the peak reaches at 4.88v at INT1 with 10ms interval.Why the fan is distorting the total waveform???angrystrange!!!I also switched on another fan in another room while on inverter.That is also distorting the signal!!!!!!!Seems the inverter is very much prone to pick up noise generated by Fan(I think....)

Last Edited: Wed. Jun 1, 2016 - 09:13 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The fan is most likely an induction motor so, it does not 'create' noise. Being inductive, the current cannot change instantly, so this causes the distortion you see. The other downside of running with a square wave is that the fan motor will run hotter.
So anything with a transformer or inductor will not like running on a square wave inverter. Things like computers don't care as they have switched mode supplies.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Okkk....so with this setup,it is not possible to control the fan speed while on inverter.........right??

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

 

Sharanyandas,

Can you use an inductor in series with your fan like the ones used on SMPS supplies. Inductor wound over a toroid.

This could help smooth out the step waveform of your invertor.

Karanbir

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I already tried with a 100uH Toroid inductor in series with the Triac(In MT1 line before the Load).But that didn't improve anything.Please suggest me if any other value Inductor is required.....

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

SHARANYADAS wrote:

Is there anything that can be done to make the circuit working for those square wave type Inverters also??And one more thing i would like to add that the circuit works on the Inverter output only on Midnight or later.....How is this even possible??

 

I'd just like to ask when is it not midnight or later?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

is the 7805 not getting hot? or have you put it on a heaksing.

also you are switching an inductive load with your simplified inverter, is it specced for that. specially motors can be a real pain in the ass for such simple sine converters.

I have seen simple inverters by the way, but a simple square wave I have not seen. normally they mimic a sinewave by having 1/3high 1/3 '0' and 1/3 low attaching an inductive load will then be a hassle for it but it will cope. now the volatge just changes from high to low an inductive load will give a very high voltage back to the inverter as it cannot immediately switch polarity.

what you could do is calculate the load of the fan and then make a low pass filter that will create a sine wave from your square wave. the voltage will drop but your fan should still run at a lower voltage