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[Reply #15 on:]

That's a "zero-cross" type, it's on page one of the datasheet.
A G3MB-202PL would be a random triggering type.

http://www.components.omron.com/components/web/pdflib.nsf/0/F1D420C93E86CDB685257201007DD5BA/$file/G3MB_0609.pdf

You can try PWM'ing your device, it won't hurt anything.  
It'll be a good lesson for you.

Ok then. Just to make sure I've got this straight:

I have the G3MB-202P - It's a Zero-Cross type, which refers to the point at which the AC current switches from positive to negative. Isn't this what I need in order to be able to switch/dim an AC source correctly?

To switch voltage on or off, yes it will work. To dim, no it won't work. A G3MB-202PL would allow you to switch on the SSR any time in it's positive or negative cycle and turn off the SSR during any zero crossing. However even with a PL device your arduino doesn't know where in the AC cycles the voltage is at any given time without some form on timing signal created from the AC voltage and inputted to the arduino. Quite complex, not impossible but you don't have the correct SSR anyway and if you are going to get something else anyway, get a AC dimming control device that can interface with an arduino, I'n sure such devices are available.
Lefty

[Reply #16 on:]

No not in this case the relay will not turn on till the AC line is low but your playing with the power and could like prolong the the time delay.

Where as on one made for phase control you fire it on using software to catch the zero cross and phase shift the power line.

With PWM you have know idea when the crossing happens.  

[Reply #17 on:]

the relay will not turn on till the AC line is low

Why is that the case?

[Reply #18 on:]

http://www.atmel.com/Images/doc2508.pdf There a link to read to get you up to speed on zero crossing

And some more http://myelectronichome.altervista.org/index.php?link=eng-il_circuito_zero_cross_detection.htm

And you may want one of these I would make my own
http://www.inmojo.com/store/inmojo-market/item/digital-ac-dimmer-module/

[Reply #19 on:]

But none of that answers the question: why wouldn't the relay turn on unless the ac line is low?

[Reply #20 on:]

the relay will not turn on till the AC line is low

Why is that the case?

It's made that way if your sitting in chair and hitting a switch and the relay is waiting to power up based on when the line becomes flat to keep a big inrush of power you could prolong the off time

Like starting a race saying go the saying stop

 

[Reply #21 on:]

It's made that way if your sitting in chair and hitting a switch and the relay is waiting to power up based on when the line becomes flat

Not sure why you think that's the case for all SSRs, or this SSR in particularly. What you described is true, in a reverse way, for SCRs and TRIACs: they will turn off at zero crossing.

Not all SSRs are made with SCRs / TRIACs and as a matter of fact, most of today's SSRs are made with serially connected MOSFETs and they do not turn off unless the current to the led side is turned off.

[Reply #22 on:]

But none of that answers the question: why wouldn't the relay turn on unless the ac line is low?

Because most common SSR relays have internal zero crossing detection and will only attempt to trigger the triac on if the input led is on AND it's AC zero crossing time. There are 'random' turn on SSRs types avalible that will trigger the the triac on anytime in the AC cycle assuming the LED input is commanded on. For both types the device can only be turned off at a AC zero crossing time.

Lefty

[Reply #23 on:]

dhenry we are not in the same boat here your talking about something beside a solid state relay
used here it's turned on with 5 volts and has zero crossing detector built in that let you turn on the relay at the cross and stop it at the cross you don't use PWM on the the firing side of the relay.
it not made for that.

[Reply #24 on:]

It's made that way if your sitting in chair and hitting a switch and the relay is waiting to power up based on when the line becomes flat

Not sure why you think that's the case for all SSRs, or this SSR in particularly. What you described is true, in a reverse way, for SCRs and TRIACs: they will turn off at zero crossing.

Not all SSRs are made with SCRs / TRIACs and as a matter of fact, most of today's SSRs are made with serially connected MOSFETs and they do not turn off unless the current to the led side is turned off.

 Oh good, another dhenry fact to deal with. Can you show me a link to a MOSFET based SSR designed to handle AC power switching applications? DC SSRs are certainly MOSFET based as SCR/Triacs would not be able to turn off a DC circuit once turned on. But I'm still of the opinion that the vast majority of AC SSR relays made and sold these days still use SCR/Triacs as the switching component, regardless of your stated fact.

Lefty

[Reply #25 on:]

How do I do that?

You need to monitor the line frequency, this is sometimes referred to as a zero-cross detector, it's easier to detect zero than it is to detect a peak or somewhere in between.

I would use a H11AA1 connected to the secondary of a transformer.  The H11AA1 output will turn on when the AC is at/near zero volts and basically be off at all other points.  So, there's the freq reference.
I would use the Arduino hardware interrupt to detect the rising/falling (as req'd) of the reference.
Then I would pulse the SSR on immediately for maximum brightness or later into the alternation (no later than 8msec, assuming 60Hz) for dimming (the later, the dimmer.)
Each cycle has 2 alternations, so there must be two triggering events per cycle (for full wave control.)
Once triggered the output will stay in conduction through the remainder of the alternation.

You can probably find more information on this in Arduino Playground.

<><> There's always X10, pretty safe stuff, very effective.

[Reply #26 on:]

And you may want one of these I would make my own
http://www.inmojo.com/store/inmojo-market/item/digital-ac-dimmer-module/

I like the idea of making my own - how would I do that?

Thanks all for the explanation on zero-crossing. I understand now!

So then, I would like to pursue both avenues - what are my options here?

Thanks!

[Reply #27 on:]

I don't no how to embed Youtube here but this shows a AC dimer I did using the pwm idea it didn't
work well
http://www.youtube.com/embed/NXdhNwEueVE?list=UUPmheWolpf9TGX-D7ch_FTw&amp;hl=en_US

If the OP ask I'll post how to wire one up using zero crossing which worked really nice.

[Reply #28 on:]

I like the idea of making my own - how would I do that?

If you want to make your own ssr, google "westhost mosfet ssr".

All you need to know about modern ssr.

[Reply #29 on:]

BTW, most of Rob's piece comes from a Vishay application note / datasheets for their ssr drivers.