I don't have much experience with solid state relays. I am going to describe my problem.

I have a SMC AC valve that I want to control with a Crydom SSR and an Arduino UNO.

When I send the signal to the SSR, it activates the valve but if I turn off the signal the valve is still running. I can only turn off the valve by cutting the AC voltage with a switch or disconnecting the voltage source.

I have measured the relay input when I send the signal and when I turn it off. I have not seen anything strange with the oscilloscope.

Can anyone give me some advice?

  • 2
    \$\begingroup\$ Minimum load current is 60 mA. Your valve is very small and your SSR is very large. Try adding a dummy load in parallel and report back. \$\endgroup\$
    – winny
    Jun 23, 2021 at 8:52
  • \$\begingroup\$ Should not, the datasheet states 0.1mA leakage current in off-state \$\endgroup\$
    – Damien
    Jun 23, 2021 at 11:04
  • 1
    \$\begingroup\$ @winny has it right - this type of solid state relay requires a minimum load current or it might stay on. Once off, your leakage spec is valid. \$\endgroup\$ Jun 23, 2021 at 19:08
  • \$\begingroup\$ @winny Thank you very much, that was the problem. The valve consumes so little power that the relay is unable to work properly. I connected a fan I had around here in parallel and now everything works without any problems. I will have to look for a more sensitive relay. \$\endgroup\$
    – Bercebus
    Jun 25, 2021 at 8:41
  • \$\begingroup\$ Or another SSR! \$\endgroup\$
    – winny
    Jun 25, 2021 at 8:51

1 Answer 1


The problem is that your very large SSR has a minimum load incompatible with your tiny (load-wise) valve.

enter image description here

Common problems with that configuration includes not being able to turn off.

Possible solutions include increasing the load to meet the 60 mA by adding a dummy load of getting a smaller SSR with lower minimum load requirement.


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