I wish to use an arduino like this with a 12v solenoid lock like this. How can I do this. I am told that using this might work, but I am also thinking I can use a transistor's amlification to do that. Can you tell which one is better and if transistor, how to do that?

  • you can definitely use a somewhat small transistor (600mA) for that. search the web for "arduino relay interface", choose a circuit, subsitute the relay with your solenoid, and you're done. Commented Nov 8, 2015 at 8:18
  • That ebay solenoid does not distinguish in its "datasheet" between its pull and hold power consumption; not does it list real and apparent/total power. Good luck sizing a transistor for that. Also if I multiply their stated current and voltage (presumably to get total power), I get less than their stated real power. Commented Nov 8, 2015 at 9:25
  • @RespawnedFluff: Since it's a DC solenoid there'll be no difference between its pull an hold power consumption except for the moment when it's first connected to the 12 volt supply. Also, since it's DC, it'll have a power factor of 1 and there won't be any "apparent power" associated with it. Finally, 12volts, DC, times 0.6 amperes is 7.2 watts, precisely what they state.
    – EM Fields
    Commented Nov 8, 2015 at 9:51
  • @EM Fields: They state 7.5W. Also look up some real solenoid datasheets and see that the activation voltage is a few volts below the nominal one, which makes their calculation even more dubious. And no, even for a DC solenoid you have different pull and hold currents. electronicdesign.com/analog/… Commented Nov 8, 2015 at 9:53
  • @RespawnedFluff: Agreed on the 7.5 watt number. However, since there'll never be anything pulling on the plunger, the hold power will be irrelevant and all that'll matter will be the 7.2 watt pull-in power required to get it moving against the spring.
    – EM Fields
    Commented Nov 8, 2015 at 10:00

1 Answer 1


By sheer luck your lock solenoid looks very similar to this one (similar spec too "Draws 650mA at 12V") and they have a working circuit for it over here so look at that and see what they used to drive it. Apparently it's a TIP120, so the peak/draw current is probably higher than that ballpark figure, which I suspect is for the hold.

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Overengineering the transistor by an order of magnitude or so (for a poorly spec'd solenoid part) ensures it doesn't go pop so easily. Also, a Darlington like TIP120 is very easy to drive from the arduino or some other microcontroller.

A similar project using the same solenoid lock used an IRLB8721 (power MOSFET) instead, which is even more beefy in terms of load current it can handle.


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