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Relay driver circuit

Discussion in 'General Electronics Discussion' started by vinod chandran, Aug 23, 2012.

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  1. vinod chandran

    vinod chandran

    Jun 21, 2011
    Hi all,
    I want a relay to turn on automatically when a sla battery gets 13.5v and turn off the same relay when the battery voltage drops below 13 or 12.5v. I am attaching the circuit which i tried and confused. Because this circuit turn on the relay but it never turn off the relay when battery voltage is below 13 , i don't know why. Any help would be appreciated. I have a couple of UA 741 op-amps to try with this circuit.
    Vinod chandran

    Attached Files:

  2. davenn

    davenn Moderator

    Sep 5, 2009
    Because the voltage source on the left is always supplying the battery and there is obviously just enough voltage on the base of the transistor to keep it conducting.
    I would assume if you disconnected the base ofthe transistor the relay would denergise ?

    why have that separate voltage source ? it should also be coming from the battery
    well I again assume that is another 14.3V voltage source you havent really stated what it is ?

  3. vinod chandran

    vinod chandran

    Jun 21, 2011
    Hi dave,
    Thank you for the fast reply. That 14.3v source is the charging voltage of that battery. All i want to toggle the relay switch so that i can charge the battery with 400mA in normal mode and 40mA in Trickle mode.
  4. vinod chandran

    vinod chandran

    Jun 21, 2011

    Attached Files:

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