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I've attempted to incorporate a discharging RC circuit that will "unlatch" a solenoid when power is turned off. However, I'm not fully confident that I've correctly designed what I hope to achieve (little circuit design experience).

The solenoid plunger holds position in both extended and retracted positions. Only a brief 100ms of power is needed to move the plunger to either state. I am using two relays, in which the 'NC' terminal is wired to the direction of current which would retract the plunger inward. Therefore, when power is turned off, the RC would discharge and retract the plunger. I am looking for review and feedback on the correctness of my approach. Advice and suggestions are welcome.

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2 Answers 2

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A single relay would do.

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On energising the relay, the capacitor charge-pulse would latch the solenoid.

On de-energising the relay or powering off, the capacitor discharge-pulse would unlatch it.

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From what you are saying, there's still a significant chance that the "hold-up" (aka energy storage) capacitor could get discharged too quickly before the Arduino had a chance to revert the latching solenoid back to "neutral" hence, I'd be looking for something more like this: -

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The diode is repositioned to prevent a loss of 12 volts discharging the capacitor too quickly. I've also moved your resistor to the positive leg (just for my convenience) but, I would question whether you need a resistor at all. Maybe inrush current limiting?

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