crobertsbmw 0 Posted August 27, 2011 Share Posted August 27, 2011 I have a circuit that I need to develop. I want to add a switch to a 220v ac source and switch it on or off with an MSP430. At first I was intending to use a solid state relay. However, I could not find an SSR that could handle 220vac, and have a coil voltage low enough to be triggered by a micro-controller, and keep the circuit inexpensive. I then looked at using a TRIAC as a switch and I bought one and was messing around with it and I couldn't get it to work the way I thought it should (it was always closed, even when I thought the thing should be open. I may have destroyed it while trying to solder leads to it). I then found out you have to "isolate the trigger." I have little idea of what that means. Does anyone know of any switches I could use for this application? Whether it be a specific SSR, or some other type of switch that I am not familiar with. If I were to use a TRIAC how do I isolate it and make it work properly? Thanks Chase Quote Link to post Share on other sites
RobG 1,892 Posted August 27, 2011 Share Posted August 27, 2011 You have to use optocoupler to isolate, very important since you are dealing with line voltage here. Look at this post. Which triac are you using? BTW, I will have several triac boards available soon. Quote Link to post Share on other sites
crobertsbmw 0 Posted August 27, 2011 Author Share Posted August 27, 2011 So do optoisolators have TRIACS built into them? So I need to buy a TRIAC/optoisolator combo correct? I have kiCad on my computer and wish I knew how to use it well enough to draw up a quick schematic to confirm how to integrate this optocoupler into my circuit. I have to have my buddy give me a crash course in kiCad sometime. Is there anything I need to know about opto-couplers when picking one out? It won't let me post off site URL's because I'm new. This is the TRIAC I was looking to use: digikey part # 568-1780-1-ND Now I am thinking of getting this: digikey part # 751-1489-5-ND Quote Link to post Share on other sites
RobG 1,892 Posted August 27, 2011 Share Posted August 27, 2011 Opto isolators do have triacs in them, but they are used to trigger main triac. Are you planning to do PWM or simple on/off? For PWM, you should use opto like MOC3023 (random phase) and zero crossing detector with another opto, 6N138 for example. If you only need to turn off/on, then get zero crossing opto like MOC3063. The triac, I would suggest getting something like BTA24-600BW or CW, it's snubberless and isolated. Also, see taydaelectronics.com or futurlec.com, they have pretty good triac prices. Quote Link to post Share on other sites
crobertsbmw 0 Posted September 1, 2011 Author Share Posted September 1, 2011 So I got all these pieces and breadboarded it up to do some testing. I can't seem to get the triac (TO-220AB Insulated) nor the opto-coupler to do what I think it should. First I tried this: and when putting 5 volts across the anode/cathode I got nothing. So I tried to look at just the optocoupler. I put 7Vpp 60Hz across the two main terminals. And the voltage across the resistor is 0 and the voltage across the main terminals is 7 as expected. When I put 5 volts dc across the LED of the opto-coupler I thought the switch should close and allow the voltage across the two main terminals should go to 0 while the voltage across the resistor should go to 7. I am finding that the voltage across the terminals remains at 7 volts and the resistor has no voltage across it (basically nothing happened). With the triac I am getting a similar problem. I can't get the switch to close and put a voltage across the load resistor. Can anyone spot what is going wrong? Quote Link to post Share on other sites
zeke 693 Posted September 2, 2011 Share Posted September 2, 2011 SCOTTY! MORE POWER! To my eyes, it looks like you need more power than the function generator is going to provide. In fact, I bet the function generator is going to output 1Vpp @ 10mA maximum. A first thought would be to study the MOC3063TVM datasheet to see at what point it triggers. That is, the working voltage and load current to make it do something useful. Also, may I suggest that you test the triac using 24VAC from a standard door bell transformer instead of the function generator? The bell transformer will lower 120VAC to 24VAC and make it less deadly to you but still provide enough current to do something. You could also put an incandescent light bulb in the load side to give you a visual indicator of your circuit function. Either that or a DVM or 'scope. On the input side, you could rig up a simple switch that applies the proper trigger voltage to the anode through a load resistor. You should tie the cathode to ground in that case. What do you think? RobG and crobertsbmw 2 Quote Link to post Share on other sites
crobertsbmw 0 Posted September 2, 2011 Author Share Posted September 2, 2011 SCOTTY! MORE POWER! To my eyes, it looks like you need more power than the function generator is going to provide. In fact, I bet the function generator is going to output 1Vpp @ 10mA maximum. A first thought would be to study the MOC3063TVM datasheet to see at what point it triggers. That is, the working voltage and load current to make it do something useful. Also, may I suggest that you test the triac using 24VAC from a standard door bell transformer instead of the function generator? The bell transformer will lower 120VAC to 24VAC and make it less deadly to you but still provide enough current to do something. Funny thing about that. At first when I was playing with it I had the leads of the triac confused and I had it hooked up to a little led. Well I started thinking I needed more power so I hooked my circuit up to the wall socket and blew up my triac mighty quick. I also blew the fuse on my function generator. I will take a second look at the datasheet, I thought I could trigger it with really small voltages but maybe i'm mistaken. Ideally I want to trigger it with an output port of my msp430 You could also put an incandescent light bulb in the load side to give you a visual indicator of your circuit function. Either that or a DVM or 'scope. On the input side, you could rig up a simple switch that applies the proper trigger voltage to the anode through a load resistor. You should tie the cathode to ground in that case. What do you think? I think it should work. I am suprised that even with smaller voltages and currents I couldn't get anything. I will try ramping up the power and see if I can get some better results without killing myself. Quote Link to post Share on other sites
zeke 693 Posted September 2, 2011 Share Posted September 2, 2011 A variable autotransformer would be nice right about now eh? Quote Link to post Share on other sites
crobertsbmw 0 Posted September 6, 2011 Author Share Posted September 6, 2011 So this is what I did. However I can't get the light bulb to switch off. At first I thought something is wrong with the optocoupler (or the way I set it up) but even when I disconnect the gate of the triac (let it float) and plug in the circuit the light is on (actually with a floating voltage it's not that odd that the bulb is on, is it?) so maybe the way I have this optocoupler set up is wrong... I followed the exact schematic that is pictured on the optocoupler datasheet for common applications. I am still baffled... Quote Link to post Share on other sites
crobertsbmw 0 Posted September 13, 2011 Author Share Posted September 13, 2011 So I think I blew my triac switch. I ended up buying some new ones, breadboarded the thing up. And now it works wonderfully. Quote Link to post Share on other sites
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