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I'm using an SSR but I would also like to be able to turn on the circuit using a switch. Can I use a switch in parallel with the SSR load outputs? This would cause a short between the terminals.

The following diagram illustrates the idea. If the SSR actually works as switch this would be ok, but I want to make sure, considering its true behavior.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Sure you can, I would like to inform you that SSR when gots damaged it usually remain in conductive mode. If the purpose is to have manual backup switch. \$\endgroup\$ Commented May 29, 2016 at 9:29
  • \$\begingroup\$ @MarkoBuršič I got what you're saying. If I was to use it as a backup switch I should place it in series with the SSR. My purpose though is only to have it as an alternative, in case people want to turn on the circuit without using the micro controller. Thanks for pointing that out. \$\endgroup\$
    – hugos
    Commented May 29, 2016 at 13:06
  • \$\begingroup\$ And that was also my thought, wit an relay and alternating switch you can turn on/off both with contrller and manual. I will post an answer. \$\endgroup\$ Commented May 29, 2016 at 14:21
  • \$\begingroup\$ You could connect that "manual" switch to the microcontroller as well. This way you can fully program the behavior of this switch in combination with whatever logic is on your microcontroller. \$\endgroup\$
    – aaa
    Commented May 30, 2016 at 5:37

3 Answers 3

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Yes.

I've been doing this for years.

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How to turn on/off in both auto an manual mode:

schematic

simulate this circuit – Schematic created using CircuitLab

The relay could be bistable with two coils that swap the position of contact.

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Yes, once the switch is closed, the SSR output is turned off, then all current will flow through the switch.

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  • \$\begingroup\$ The switch will have a near zero volt-drop. The triac will be about a volt. The current will flow through the switch whether the SSR is on or off. \$\endgroup\$
    – Transistor
    Commented May 29, 2016 at 19:18
  • \$\begingroup\$ After OP edit. This still isn't quite right. Depending on the SSR triggering arrangement the SSR could still be turned on but not conducting because the switch has lower resistance. If the switch is opened mid cycle the SSR would conduct in this case. \$\endgroup\$
    – Transistor
    Commented May 30, 2016 at 6:19

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