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Assuming I have a relay module (I'm not sure about its features) that is connected to a 12 V DC solenoid valve and should be operated by a microcontroller.

  • Do I need a flyback diode connected with the relay module? -Do relay modules usually include flyback diodes?
  • What about the solenoid valve - does it need its own flyback diode or is it unnecessary?
  • Finally, do I need to make sure that opto-coupling is provided?
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    \$\begingroup\$ DC or AC solenoid valve? Edit the details into your question. \$\endgroup\$
    – Transistor
    Commented Oct 11, 2020 at 22:33
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    \$\begingroup\$ @Transistor I've just edited it. Thanks very much for your concern. \$\endgroup\$
    – Doua Ali
    Commented Oct 11, 2020 at 22:38
  • \$\begingroup\$ The following posts might help: (1) Flyback diodes for solenoid": raspberrypi.org/forums/…, (2) "Flyback diodes selection": raspberrypi.org/forums/… \$\endgroup\$
    – tlfong01
    Commented Oct 12, 2020 at 0:38
  • \$\begingroup\$ What's a "relay module"? Could be anything from a plastic bin with a relay inside to a PLC. \$\endgroup\$
    – Lundin
    Commented Oct 12, 2020 at 6:12

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the relay module will include a flyback diode, but that diode is only foir the relay itself. you will need another diode for the solenoid.

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  • \$\begingroup\$ Thanks very much. Is 1N4007 fine as a flyback diode for a 12 V/ 2 A DC solenoid valve? and will connecting a flyback diode dramatically slow down the operation of the solenoid valve? \$\endgroup\$
    – Doua Ali
    Commented Oct 12, 2020 at 0:41
  • \$\begingroup\$ 1N400x are good for 1A average current, used with a 2A solenoid it will see 2A peak current (and usually much less) so it should be fine. \$\endgroup\$ Commented Oct 12, 2020 at 1:13
  • \$\begingroup\$ Thanks a bunch for your useful info. Excuse me, if the relay module provides optocoupling, do I still need to use a separate power source for the relay module (VCC) other than that of the microcontroller? \$\endgroup\$
    – Doua Ali
    Commented Oct 12, 2020 at 22:23
  • \$\begingroup\$ the best I cab say there is maybe, \$\endgroup\$ Commented Oct 13, 2020 at 6:27

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