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Car voltage monitor

Discussion in 'Electronic Basics' started by Grey, Aug 9, 2005.

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  1. Grey

    Grey Guest

    I do a lot of work from my car, which is brand new. But I had some current
    leakage somewhere and the battery drained away and I was stuck.

    What I would like is a small LED which would warn when car battery falls to
    a critical level at the point where I cannot start. To save pulling more
    power, I would be an idea for it itself to be powered by a small battery. A
    better idea would be a tri color LED to indicate full- 50%-0 charge, but
    pull little current from the car.

  2. JeffM

    JeffM Guest

    ...I would like...a small LED which would warn
    Won't work.

    Some concepts you don't grasp:
    Thevenin resistance
    Kelvin sensing

    Why not get the actual problem repaired?
  3. kell

    kell Guest

    Did the car itself have current leakage or did the equipment you
    installed in it to do this work you mentioned cause the problem?
  4. Redink

    Redink Guest

    I don't think their is any actual problem since car battery if not used
    will drain away.
    their can be a way to do this it's rather simple actually

    take a voltameter and hook it up to the car battery and make sure the
    current is passing and showing up.

    now unconnect it and do the following

    now take the voltameter and open it up and make a seriously small hole
    in the board of the voltameter that tells you what is the number of
    volts (Board that you read to know what current it is passing) put a
    new piece of wire through it and make sure it touched the glass of the
    thing if you want make a hole in the glass also and pass the wire
    through and tie it up on the glass or soilder it
    lol also make sure that the needle is to the right of that wire first
    now hook a wire from one point of the voltameter's wired (those red and
    black) take the red one and hook it to the needle but make sure the
    needle can freely move.

    now take the LED and connect the shorter side to the black wire and the
    longer side to the wire we just put through the voltameter.

    if you followed what i just tried to say you will understand that
    basically the voltameter will act as a switch when ever the voltameter
    has a certain voltage the needle will touch the wire we put through and
    hence completing the circuit and hence lighting the LED if the power is
    full the needle will not touch the wire and hence breaking the circuit
    and not lighting the LED

    if you did not understand any thing or some thing just say so and i
    will try to my best to explain it in detail

    and ya do measure some safty k m8 car battery packs quite a punch and
    you might get some serious harm done to your self or some thing.

    Basic rule to follow for Safty never touch two different wire at the
    same time and never touch a wire that is touching two different wire
    either. :D




    You cannot test your car battery's capacity to start your car without
    putting a load on the battery. The act of testing the battery diminishes
    its capacity.

    You would need some device that intermittently load tests your battery and
    sounds an alarm if it is below a certain threshold.

    Seems like the wrong approach.

    Does this problem occur in the morning when you go to start your car? The
    battery was slowly drained overnight? One possible cause is the battery has
    internal leakage, just because it is a new car does not mean the battery has
    to be good.

    Or, you are correct and one of your electronic devises is drawing current
    and needs either repaired or unplugged when the car is shut off.

    Are any of the devices battery powered and charging batteries while plugged
    in, if yes, you may have a faulty battery in that device or the charging
    circuit in that device is faulty.

    If you have allot of electronics in your vehicle you may just want to have a
    second power port wired in and done in a way that when the key is off or not
    in the "Acc." position the power port is shut off.
  6. Rich Grise

    Rich Grise Guest

    Then the first thing you do is take it back to the guy that you bought
    it from "brand new" and have it replaced by a car that works.

    Good Luck!
  7. ehsjr

    ehsjr Guest

    What is the point of a LED telling you that the battery has fallen
    to the critical level? At that level, per your statement, the car
    won't start. The LED lights up too late to be helpful.

    Suppose you design it to light up one hour before the battery
    falls to the critical point. You park your car, and the LED
    lights up while you are gone. What good does it do? If you
    come back in less than an hour, you'll start the car anyway,
    with or without an LED. If you come back in over an hour, the
    LED doesn't help - you still can't start your car.

    In short, you are proposing/requesting a useless device.

    Get the car fixed.


    To save pulling more
  8. Bob Monsen

    Bob Monsen Guest

    When you say you do work from your car, are you talking about running a
    laptop, an inverter, or just letting it sit there while you go off and
    do something else?

    Whatever the reason, you can buy portable batteries that can be used to
    jump the car. They are about $50, and sit in your car, plugged in to a
    lighter socket. If you drain the battery for some reason, you can use
    them to start it. Here is an example:

    RV folks tend to use them, because RVs have the same problem with
    drained batteries when parked for long periods.

    Bob Monsen

    If a little knowledge is dangerous, where is the man who has
    so much as to be out of danger?
    Thomas Henry Huxley, 1877
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