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Topic: Arduino Solid State Relay Control (Read 7398 times) previous topic - next topic


Hi there, I'm testing the control of a solid state relay from my Arduino Mega, and have the thing wired up like this:

I have the following SSR (SSR-25 DA):

The SSR is connected to mains and should, I believe turn the light bulb on when I send a digitalWrite HIGH to the relevant pin, and I can see the LED built into the SSR turn on when this happens, and after 10 seconds when I wrote a LOW to the same pin the LED in the SSR turns off. Mains is 240V AC / 10A.

The problem is that the light bulb does not go on. When I replaced the light bulb with a multi-meter I could see when HIGH is written about 23-24V goes through, well short of the 240V from mains.

Could the SSR be faulty? Or am I missing something really obvious (I am new to this)  :-)



Sorry, originally posted in home automation since this is part of a home automation system :-)

Any ideas? Should I just try another SSR, from another manufacturer?

Thanks all!


23-24V goes through

Where are you measuring that voltage? Does you meter read correctly if you check your power source, the mains supply?

mains supply leg1......bulb....relay....leg2

Do you get 240volts from leg1 to leg2?
With the relay turned off do you get 240v across the relay?
With the relay on what voltage do you measure across the relay?
Stupid question but, is your bulb a known good one?
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com


Where are you measuring that voltage? Does you meter read correctly if you check your power source, the mains supply?

Hi there, I can confirm that the meter is fine, it reads the full 240 volt (a few more but I guess that is expected) from the mains. The bulb is good and tested with a straight mains connection.

I am testing across the high voltage capable SSR output connectors (which say 24-380VAC next to them), not the lower voltage input control connectors of course (which say 3-32VDC next to them). Unless the label on the SSR is incorrect, it is a cheapie, but I would hope that would not be the issue, and I definitely don't want to run 240V AC through the other connectors!

Do I need a resistor on the control side? Apologies if that seems like a silly question, I assumed not since an SSR (according to what I have read) should be a lot easier to drive than a mechanical relay, where I've read it can blow the Arduino if not set up correctly.

Thanks for the reply :-)


Assuming the relay is good, that diagram is correct.  I just hooked up a similar relay last week.

Did you remember to set the pin you are using to output?
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com


Thank you all for your posts! Notch this one up to a Newbie error. I had mounted the light socket on a piece of plywood, and during that process one of the cable in that socket came loose. Once this was rectified it all worked.

I found this by testing the light directly with no relay in the path, just plug cabled straight to socket. When that didn't work I had my answer :-)

Now I just need to figure out how to dim lights, but that's for another post (only if I get stuck!)  :-)

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