Hi Adam,

Thanks for the suggestion! I connected a 39 ohm resister and 0.01uF 
capacitor across the triac as a snubber and it fixed the problem. However, 
in so doing the snubber is connected in series with the load as well as the 
110V mains, there is in theory a small current flowing through the snubber 
all the time even when the triac is off, does this matter?

John

>From: "M. Adam Davis" <stienman@gmail.com>
>Reply-To: "Microcontroller discussion list - Public." <piclist@mit.edu>
>To: "Microcontroller discussion list - Public." <piclist@mit.edu>
>Subject: Re: [EE]: How to turn off Triac Output Optoisolator?
>Date: Wed, 13 Sep 2006 17:03:13 -0400
>
>The AC motor is likely producing enough inductive kickback to prevent
>the triac from shutting off.
>
>Investigate snubber circuits.  Many triac data sheets contain
>information on a reasonable snubber.
>
>The circuit at the bottom of my webpage:
>http://www.ubasics.com/adam/electronics/doc/phasecon.shtml
>Has a snubber in it, consisting of the 39 ohm resister and the 0.01uF 
>capacitor.
>
>This data sheet has a few different configurations for snubbers as well:
>http://www.ubasics.com/files/lightdim/moc3010.pdf
>
>You might find other information by doing a search for "triac
>inductive load" or "triac snubber"
>
>Good luck.
>
>-Adam
>
>On 9/13/06, John Waters <john_fm_waters@hotmail.com> wrote:
> > Hi All,
> >
> > I'm experimenting the MOC3023 Triac Output Optoisolator.
> >
> > In the first experiment, I connected a 4.7K resistor (as load) in series
> > with the output Triac and used a signal generator to provide a 3V ac 
>(peak
> > to peak) as power source. I then applied a 6V d.c. to the input LED 
>through
> > a 1K resistor connected in series. There was current flowing through the
> > load immediately.  When I connected the input to 0V, the triac cutoff 
>and no
> > current flowed through the load.
> >
> > In the second experiment, instread of using the low voltage ac from the
> > signal generator, I used a 10V ac (rms) stepped down from a power
> > transformer as power source for the load. I also changed the pure 
>resistive
> > load with a small ac motor that consume very little power. This time, 
>when I
> > applied a 6V d.c. to the input, the triac would be turned on 
>immediately,
> > however, if I applied a 0V to the input, current would continue to flow
> > throught the load, the triac would only cut off when I manually 
>disconnected
> > the ac power source.
> >
> > I want to know what causes the differences between these two 
>experiments. In
> > fact, my application requires to use the input alone to turn on/off the
> > triac (like what was doing in the first experiment), is there any way to
> > achieve this?
> >
> > Thanks in advance!
> >
> > John
> >
> >
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