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Battery cut-off switch

  1. Dec 7, 2015 #1
    How battery cut off switch works??
    How to apply Battery cut off switch on a vehicle..??
    I want to make some electric functions to be operated if the battery is cut off.
    For this what should I do..??
  2. jcsd
  3. Dec 7, 2015 #2


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    Your question is completely unclear.WHAT battery cutoff switch? What is it on? What are you talking about?

    Normally a "cutoff" means exactly that ... it cuts something off (not physically cut, but "turned off")
  4. Dec 7, 2015 #3


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    This is not a Classical Physics topic so the moderators may move it to Engineering -> Electrical ?

    Normally a battery cut is located very close to the battery where there is just one or two wires wire providing power for everything. So if you install a cut off there it will turn everything off.

    Some vehicles have more than one fuse box. It might be possible to install a switch so that it turns off power to one fuse box and leaves power connected to another fuse box that has the functions you want to keep.

    You will need a circuit diagram for the vehicle and an auto electrician.
  5. Dec 7, 2015 #4
    actually cut off switch refers to a switch that turned off power from battery so that discharging of battery could not occur when the vehicle is switched off.
    But If you completely cutoff the battery (power from battery) by turning off the cutoff switch, then no electric equipment can be operated until or unless cutoff switch is turned on.( I am not sure whether ignition switch works or not)
    On some vehicle, hazard light and back lamp still be operated if cutoff switch is turned off.
    I want to know how do it works..??

    Got my point..??
  6. Dec 7, 2015 #5
    @CWatters I am new to physics forum so if this thread should be in electrical section, then they may shift it.

    From your reply,
    If I want to operate hazard light even cutoff switch is turned on then I should supply power at those fuses belongs to hazard light so it can be operated when every other thing can't be..?
  7. Dec 7, 2015 #6


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    Yes that's the idea, however it might not be a simple job...

    The battery side of all the fuses is probably connected together - perhaps by a track on the printed circuit board that mounts the fuses. So if you just connect power to the battery side of the hazard light fuse it will "back feed" to all the other fuses so everything will get power. You might need to insert a blocking diode or modify the wiring in other ways.

    There might also be issues with the system that detects if a bulb has blown.

    On modern cars disconnecting the battery can also cause issues for things like the radio and the alarm.
  8. Dec 7, 2015 #7
    For my case there would be another problem that if we cut the battery off when the engine has been started then other equipment would be turned off. But at that moment If ignition switch is turned off, then switch/engine will not stop as no power would be there to operate ignition switch/motor (or may be it called stater motor). In that case how I can turn my engine off..?? should i supply power from Alternator to ignition switch..?
    what should I do?
  9. Dec 7, 2015 #8
    One thing you could do if your main battery was for some reason disabled, is you could have a backup battery which would not be strong enough to start the motor, but still good enough to keep radio and lights etc going.
    You could have a switch to connect that battery if it becomes needed, otherwise it's not in use.
  10. Dec 8, 2015 #9

    jim hardy

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    Some places sell a battery with a cord that plugs into the cigarette lighter.
    On my Ford Escort my rechargeable flashlight , when plugged into the lighter keeps the radio going with ignition key off. (That was not by design and i'll be fixing the flashlight so it can't backfeed the car... )
  11. Dec 8, 2015 #10


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    Ok, this post shows me that you have a lot to learn about automotive electrics. You cannot expect answers with your current level of understanding. First thing to always remember is to NEVER DISCONNECT A VEHICLE BATTERY WHILE THE ENGINE IS RUNNING! This will cause the system voltage spike well above operating voltage due to the nature of the charging system.
    I have no idea what you are talking about referring to
    This makes no sense. The starter is there to spin the engine in order to draw fuel and air in and start the process. It has nothing to do with shut-down. You are wandering into such unfamiliar territory that I believe you will become very confused and discouraged if you don't stop and learn some basics first. Or worse yet you will become hurt.
  12. Dec 8, 2015 #11

    jim hardy

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    are you adding a battery cutoff switch to a vehicle? I thought you were describing a vehicle with one already in it.

    We could only guess.
    There's several ways to accomplish what you have so ambiguously described.

    It's a safe bet they are not powered through the cutoff switch.

    Get a shop service manual for the vehicle in question and study the wiring diagram. We can help if you post it.
  13. Dec 9, 2015 #12
    yes you are right.
    I will get back to you as I gain some basics to do this sort of changing.
  14. Dec 9, 2015 #13
    A way of designing this is first to figure out what voltage causes the turnoff. Then you could use a comparator to measure when this cutoff is reached. When the cutoff is reached, you could make separate circuitry that could do whatever you want at this point. This is how I would pursue it.
  15. Dec 17, 2015 #14
    I have found that Battery cut off switch is basically a Battery Relay controlled by a switch that turned it on/off as per requirement.
    And also I have found a solution to my case.
    Thanks for your sharings.
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