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555 timer control of solenoid actuator

Discussion in 'Sensors and Actuators' started by rogierk, Feb 8, 2010.

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  1. rogierk


    Feb 8, 2010
    I have this monostable 555 timer circuit that works fine with a LED (+resistor), but with a 12V solenoid actuator, it just opens but it does not close. The solenoid works fine when connected directly to the 12V source. Ideas about what could be wrong would be very welcome.

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  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It sounds like your 12V solenoid requires more current than the 555 can supply.

    Have a look for 555 circuits using a bipolar transistor, a mosfet or a relay to drive heavier loads.

    Also don't forget to place a diode across your solenoid (or relay if you use one) to protect your 555.

    This has a few examples.
  3. rogierk


    Feb 8, 2010
    Thank you *steve*, that is very helpful. If the current is too low, how come the solenoid stays open? Does it prevent the timer from running out?
  4. Resqueline


    Jul 31, 2009
    A 555 is rated to supply up to 100mA. Above that the output voltage sags.
    A relay & a solenoid requires a lot more current to pull than to stay pulled.
    Example; a 12V relay may pull at 9V but may release at only 3V.
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