RE - Car Cigarette Lighter Powered Garage Key Fob

Discussion in 'Power Electronics' started by LiamGorham, Aug 2, 2017.

  1. LiamGorham

    Thread Starter New Member

    Aug 2, 2017
    2
    0
    Good Morning Everyone!

    Hopefully someone will be able to help, We're looking to try and get the garage keyfobs (3 simple button fob) that open and close the Garage door but have it as a perm item powered by the cigarette lighter. It's hard to explain exactly so i've included below a link to an item very similar (sadly it wont work with our Mhz gagage door)

    https://www.ebay.co.uk/i/1822862577...=9045311&device=c&campaignid=857333952&crdt=0

    Would there be a way to take the internals of a current keyfob and convert it to be powered via the cigarette lighter? I was possibly thinking down the route of an USB end to the battery sections of the internals of the current normal fob however i'm worried about amp-age etc (the fob runs off on a A27 battery) which i believe only about 25 mamp but 12V - A USB would be 5V and 500mamp, Not enough voltage to power but enough amps to most like damage the circuits.

    Any ideas on how i can convert this keyfob to be powered of either USB (can then just connect to a USB lighter socket bit) or any other ways?
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    7,421
    1,754
    Welcome to AAC!

    Just wire the battery holder terminals to the cigarette lighter. You could include an in line fuse if it makes you feel better.
     
  3. LiamGorham

    Thread Starter New Member

    Aug 2, 2017
    2
    0
    Would that not kill the fob? It's a US mustang, the cigarette lighter would punch out between 2 and 12 amps which would fry a fob designed to take only 0.025 amps?
     
  4. ebeowulf17

    Distinguished Member

    Aug 12, 2014
    2,558
    474
    Ohms law.

    The 2-12 amp spec represents the maximum amount of current that cigarette lighter outlet CAN provide, not what WILL flow from it. The current through the fob is determined by the resistance of its circuitry and the voltage it's provided. If you provide it with the same voltage it "expects," then it'll draw its normal amount of current.
     
  5. dl324

    AAC Fanatic!

    Mar 30, 2015
    7,421
    1,754
    That's a common misconseption by novices. The remote will draw the current it requires to function. The fuse I suggested was to make you feel safer.

    A car cigarette lighter could supply as much as 13.8V when the engine is running, but 12 volt devices should operate at that voltage because a fully charged 12V battery will be higher than its nominal voltage. If you're concerned, you could install a couple diodes in line to drop it to 12.4V.
     
    ebeowulf17 likes this.
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