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5 volt solenoid

Discussion in 'General Electronics Discussion' started by Tony1958, Mar 22, 2014.

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  1. Tony1958

    Tony1958

    2
    0
    Mar 22, 2014
    Hi

    I'm new here but hoping someone can help.

    I haver two small 5v pull solenoids connected to an arduino board via a TIP 102 power darlington pair with integral diode.

    The arduino activates the solenoids for a preset time determined by the programme. All works fine and the solenoids activate correctly. However when the TIP 102 is turned off the solenoids stick pulled in. If you tap the ends they return normally. At first I thought this was a mechanical problem but it's not as the solenoids don't stick when not first energised. I thought there may be a problem with the circuitry so I connected the solenoids directly to the arduino's 5V supply line driven from the USB on my computer but they still stick open - sometimes not all the time. They still stick open when disconnected from the supply and even when you short the terminals of the solenoids they still stay pulled in. It is as if there is residual magnetism holding in the plungers?

    This is really making me pull my hair out as everything else works fine except these damn things.

    Anyone got any ideas?

    Tony
     
  2. duke37

    duke37

    5,299
    739
    Jan 9, 2011
    The TIP102 has a diode to prevent reverse voltage across the transistors. It does NOT have a diode to protect the device from exess voltage. For this you need a diode connected across the solenoid in a direction that does not normally conduct. Alternatively you can connect a resistor across the solenoid with a value about the same as the solenoid or a bit higher but this wastes power.

    Sticking of magnetic actuators can occur due to some residual magnetic field. A spring to force the solenoid back can be used or a small adjustable brass screw to stop the solenoid closing completely. I dealt with an electric fence energiser which had a relay operating about once a second. This would stick and the little screw had to be adjusted now and again. I replaced the relay with a thyristor.
     
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