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Transistor as a relay

  1. Jul 23, 2014 #1


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    I'm looking for some help setting up a circuit system. Were currently using a magnetic type trigger relay. Im trying to get a quicker release of the circuit. Its for the trans brakes on our drag cars.
    Here is what i was thinking, this is of course a very rough and first draft of my thoughts. Im not sure how transistors work or what kind of problems i would have doing this but im willing to learn.

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  3. Jul 23, 2014 #2


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    hi there

    not quite drawn like that but a close attempt :smile:

    before a suitable transistor could be suggested, we would need to know the current in Amps that the solenoid requires to be operated. as the transistor would have to switch this amount of current

  4. Jul 23, 2014 #3


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    Ya, my paint drawing skills suck, but you get the idea i guess. No more than 10 amps, some solenoids pull 1-2 some pull 5-6. 12 volt systems. The solenoid will be triggered for no longer than 10 seconds at a time, since with a couple types of trans brakes. You have to use the brake for reverse. Though i would like the circuit to be able to handle 20 amps at a minimum.
  5. Jul 24, 2014 #4

    jim hardy

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    I gather there's a noticeable delay now between operating your switch and the actual solenoid release?

    Help the folks here help you.....

    two questions that'll help get you an optimal fix:

    1. Is there a datasheet or part number for the relay, and one for the brake ?

    It's possible that your delay is in the brake solenoid itself.
    If it is equipped with a "flywheel diode" to protect your mechanical relay or switch contact from arcing ,
    a faster electronic relay would still have to wait while the solenoid's coil discharges into that protective flywheel diode.
    Might be that just a tweak of that protective circuit would do the trick for you.

    2. Do you have access to the solenoid's ground wire?

    Sometimes it's easier to place an electronic switch in that wire than in the "hot" one..

    old jim
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