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Will back feeding 12v INTO the cigarette lighter cause any damage?

Discussion in 'Gen 3 Prius Main Forum' started by Johnny Cakes, Oct 11, 2021.

  1. Johnny Cakes

    Johnny Cakes Senior Member

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    The "WHY" is a long story and not really relevant. The question is whether back feeding 12v into the cigarette lighter will cause damage?

    Interestingly, when 12v is connected to the cigarette lighter, the Prius acts like it is in ACC mode. In other words, the exact same sequence occurs as if if you pressed the starter button once (beeps, radio start, etc).

    Anyone have any thoughts?
     
    #1 Johnny Cakes, Oct 11, 2021
  2. vvillovv

    vvillovv Senior Member

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    I can't give feedback on the question cause I don't know. The question is interesting enough to check on what's out there on the subject.

    Here is one that addresses one way of backfeeding the cigarette lighter in general, not prius specific.
    https://mechanics.stackexchange.com/questions/15893/is-it-possible-to-charge-car-battery-through-cigar-lighter-socket
     
    #2 vvillovv, Oct 11, 2021
  3. jzchen

    jzchen Newbie!

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    No damage some jump starters are designed to connect there. Makes for a nice comfy place in inclement weather.

    (In other words the fuse does not know which way it is inserted. Can install it either way it still works).

    REVVL V+ 5G ?
     
    #3 jzchen, Oct 11, 2021
    Last edited: Oct 11, 2021
  4. Johnny Cakes

    Johnny Cakes Senior Member

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    Thanks -- it still kinda bothers me that doing that causes the car to go into ACC mode by itself.

    Obviously connecting 12v to the battery doesn't cause the car to go into ACC mode, so its just unnerving that connecting 12v to the cigarette lighter does. Something odd is happening.
     
    #4 Johnny Cakes, Oct 11, 2021
  5. jzchen

    jzchen Newbie!

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    (You just reminded me).

    There are CANBUS chargers/maintainers that use the cigarette lighter outlet. A lot of vehicles the cig lighter is disconnected unless the vehicle is at least in ACC or ON. I saw them at a friend's/acquaintance's house plugged into the cig lighter socket. In those vehicles I knew that the outlets are off unless the vehicle is in ACC or ON. So what you have plugged in must be one of these (magic to me) CANBUS enabling units.

    I can see how that would be an issue if the whole car is basically awake/in ACC mode....

    REVVL V+ 5G ?
     
    #5 jzchen, Oct 11, 2021
  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    The accessory socket is connected to the accessory bus. If you put power into the socket, you should expect the rest of the bus to be fed as well.

    Nothing mysterious about it; nothing dangerous either.
     
    #6 Leadfoot J. McCoalroller, Oct 12, 2021
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  7. privilege

    privilege Active Member

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    can you run the wipers, windows, lock/unlock, fan/ac after it's powered on (acc) via plugging in a 12v to the socket ?
     
    #7 privilege, Oct 12, 2021
  8. Johnny Cakes

    Johnny Cakes Senior Member

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    I thinks so -- it seemed to be 100% ACC

    Makes perfect sense -- thanks!

    Just in case someone finds this thread via a search in the future.....

    I don't want the accessory bus to be hot. I considered adding a diode, but didn't have any around. I did have the circuit board (link below) lying around, which selects a DC source based on priority and then feeds the load. It also isolates the two DC power sources. Six simple screw connections and I was done.

    Thanks to all who helped!

     
    #8 Johnny Cakes, Oct 12, 2021
  9. sam spade 2

    sam spade 2 Senior Member

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    Indeed.
    But IF that socket is designed to go dead after the car is OFF for a while, then applying external power to it might make something "wake up" and go into ACC mode.
     
    #9 sam spade 2, Oct 12, 2021
  10. sam spade 2

    sam spade 2 Senior Member

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    Well then I think you should consider making your connection some OTHER way.
    And just got to ask:
    What exactly is it that you are trying to accomplish by doing this ??
     
    #10 sam spade 2, Oct 12, 2021
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