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How to trigger solenoid with very low current?

Discussion in 'General Electronics Discussion' started by Kjetil, Jan 24, 2017.

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  1. Kjetil

    Kjetil

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    Jan 24, 2017
    Hi, I would like to use a very low current (something like 5-20 milliamps) to trigger a 9V solenoid. Since this very low current cannot be used directly, I am guessing that I need something like a relay switch. For the record, I am a complete novice when it comes to these kind of things!

    My question would then be, is this at all possible? If yes, what do I need in order to make it work?
     
  2. Alec_t

    Alec_t

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    Jul 7, 2015
    Welcome to EP.
    How much current does the solenoid draw when supplied with 9V?
    Can you post a link to the solenoid spec?
     
  3. shrtrnd

    shrtrnd

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    457
    Jan 15, 2010
    Can you supply the information Alec_t asked for? That would help.
    In your situation, without knowing your application, you are on the right track considering using a relay to
    control a required current to the solenoid. HOWEVER, the only thing a relay does, is apply some other
    power supply value (the current you need to activate your solenoid). A relay by itself doesn't supply it's
    own driving current to the solenoid. Just wanted to point that out in case you don't know it.
    Can you tell us more about your application? We can probably offer good advice if we have that.
     
  4. Kjetil

    Kjetil

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    Jan 24, 2017
    Thanks for your replies!

    As far as I understand the solenoid will draw something like 0.5 amps. Here is a link to the basic specs:

    http://vi.raptor.ebaydesc.com/ws/eB...244&category=181878&pm=1&ds=0&t=1485290605105

    Yes I understand that the relay will not provide a current by itself, but that is a fair question considering my level of knowledge:)

    Basically, what I want to do is to build a kind of touch-sensitive sensor that should trigger the solenoid. My plan was to use thin parallell metall wires (that does not touch each other), spaced a millimeter or so apart, hooked up to a 9v battery. Then relying on a hand/finger to close the circuit. This weak current would then activate the relay switch, triggering a higher current to the solenoid.

    Not sure if this makes sense at all..

    Once again, thanks for your help. Its much appreciated.
     
  5. BobK

    BobK

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    1,676
    Jan 5, 2010
    You are expecting 5 to 20 mA through the skin? Think again. 10 mA would be a painful shock.

    But don't worry too much, with 9V you would be lucky to get 10 μA, which is nowhere near enoufh to trigger a relay.

    You need a touch sensitve switch circuit to do what you are trying to do.

    Bob
     
  6. Kjetil

    Kjetil

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    Jan 24, 2017
    Thanks for the tip!
     
  7. Kjetil

    Kjetil

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    Jan 24, 2017
  8. Alec_t

    Alec_t

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    Jul 7, 2015
    Difficult to say from the write-up for that switch. If it's too sensitive you may find that 1.5 metres of wire makes a good enough antenna to pick up sufficient interference to give false triggers.
     
  9. Kjetil

    Kjetil

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    Jan 24, 2017
    Hm..good point. However it says that it should be possible to adjust the sensitivity. Think I'll buy one and give it a go. Not a huge investment in any case. Thanks for the reply!
     
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