I'm working on an SSR control for an air conditioner.
The relay is the Kodak 611490 and I haven't been able to find a datasheet.
Just for test purposes, I have the input connected to digital pin 4, and a sketch that just toggles that high/low with a delay long enough that I can see it on my cheapo DMM. I know this part works. (i.e. voltage pin-ground is 5, and it's drawing 4.5mA, when on)
To check the SSR, I switched to measuring resistance across the load leads, but saw nothing on my meter. So I switched to measuring the voltage of a LiMn (nominal 3.7V) cell in series with the load side of the SSR. I thought I'd get something like the voltage of the cell, less the drop of the SSR circuit, and then close to 0. On my charger, a full charge on the cell is 4.1V. What I measured was the voltage going between 4.1 and 2.5V as the Uno switched the SSR on/off. This wasn't what I was expecting. Here's my test wiring.
Then I called myself a dummy for testing with DC, when the SSR might need to see a zero-cross to turn off. So I dug out a 12VAC wall wart. My meter reads it at 13.5. Now, when I'm toggling the SSR on/off, the voltage switches between 13.5V and 4.1V. (Left the above DC test results there, in case that's informative for some reason.)
I understand there's some leakage current even in the off state. I don't know the input impedance of my meter, so I'm wondering whether it's reasonable to think that maybe the resistance of the SSR when off is roughly half of my meter's impedance.
Yes, I ought to acquire some decent test equipment. 