Using a 12v relay in a 4v circuit

Discussion in 'The Projects Forum' started by OigMan, Jul 30, 2014.

  1. OigMan

    Thread Starter New Member

    Jul 30, 2014
    This might be a bit of an odd one but I am using an 18650 battery as a power source which puts out about 4.2v on a full charge and as many as 20 amps. I am trying to use a relay in my circuit but am having trouble finding a 4v relay that will support more than 1 amp. I was thinking about using 3 18650 batteries to be able to run at 12v high amp relay but I would then have to reduce the power down to 4v before it reaches the kanthal heating element. Is there any way to use a 12v relay in a 4v circuit?
  2. MaxHeadRoom


    Jul 18, 2013
    Use a 3v-35v SSR.
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    There are plenty of 5v relays.. but what exactly are you trying to do.
    A relay has a coil (that you apply voltage to and it uses a small amount of current).
    that coil switches a set of contacts magnetically to create a circuit just like flipping a manual wall switch.
    The "contact" side is isolated from the "coil" side and is commonly switching a different voltage/current level or the same.

    So are you using this 4v source to turn on the coil side and then also using the same 4v to turn on a heating element (e-smoke or dab vaporizer.. I'd guess)
    What is the "on" button?
    What is the resistance of your heating coil?

    Just because a battery could deliver 20A doesn't mean it ever will
  4. OigMan

    Thread Starter New Member

    Jul 30, 2014
    Thank you for the quick reply and while this would likely do the trick I freer that it is to large as space is a limiting factor

    Mcgyvr, you are correct this is for an electronic cigarette. I have a 4v high amp current that I am trying not to run though the switch just to be safe because 20 amps is a lot of current to put though most momentary switches. Not to mention the only high amp switches I could find can only be activated with 12v of power

    I have worked with relays before but only in 12v circuits, honestly I have only worked with 12v systems period as the only time I am doing any kind of wiring its usually on my car or truck
    Last edited: Jul 30, 2014
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
    Do you need something like this but I presume you aren't in the UK?
  6. OigMan

    Thread Starter New Member

    Jul 30, 2014
    That looks like something that would be useful to me yes and you're correct I am in the US. Awesome find though thank you, maybe I can find that here.
  7. inwo

    Well-Known Member

    Nov 7, 2013
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    and the resistance of your heating coil is....?

    If your voltage is 4V and your coil is 1 ohm..
    Then the max current you will draw from the battery is 4/1=4A
    If a 2 ohm coil 4/2=2A

    You probably don't have a .2 ohm coil so you will never have 20A..
    hopefully you aren't one of those silly cloud chasers.
  9. takao21203

    AAC Fanatic!

    Apr 28, 2012
    you should use a MOSFET
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
    as max said before, use a ssr. a solid state relay with an input voltage of 3 to 35 volts at very low current. just make sure it is a DC ssr. a simple 4 connection fairly small block of eoxy.