car battery tester ...!!

Discussion in 'General Electronics Chat' started by flashking, Oct 20, 2009.

  1. flashking

    Thread Starter New Member

    Oct 20, 2009
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    hi,

    i have a pic , i need the component value if u can help me ...


    [​IMG]


    i need value and serial number of transistor, diode, zener diode and resistors.
     
    Last edited: Oct 20, 2009
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Let me guess: the transistor-like devices are TL431/LM431s. Let me guess further: this is a three-step voltmeter where the Red led lights up if the input voltage > 14.8V, the Amber Led lights at <12.8V, while the Green Led is on from 12.8 to 14.8V. If not, that's the way it should be :p
     
  4. SgtWookie

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    Jul 17, 2007
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  5. flashking

    Thread Starter New Member

    Oct 20, 2009
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    thnx alot .... :confused: but i need ur help to know type of transistor and diodes ....
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Something like this:

    [​IMG]
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Since it is for a car, then these trip points are useless. First, for modern cars, the normal charging voltage (with engine running above 1500RPM, engine warmed up), is 14.2 to 14.5V.

    If the alternator quits, you would like to know that. This means it is your battery that is holding up the bus voltage (for now). The battery almost immediately drops to ~12.65V, and then discharges downward from there with no alternator on line.

    If the voltage regulator shorts, applying full-field excitation to the alternator, the voltage shoots up held down only by the battery, you cook the battery, then damage appliances, so you would like to know that.

    Vbat >14.7V, light the RED led, you have a runaway alternator.

    Vbat < 12.7V, light the AMBER led, your alternator is not charging.

    Otherwise, light the GREEN led.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, but it depends...

    Some vehicles have their charging system set up for Optima batteries. These tend to "live longer" if they're charged at a somewhat higher voltage; closer to 15v. But on a typical vehicle, I've found that once the battery is pretty well charged up, the nominal system voltage is 13.8v to 14v.

    This condition is usually indicated by the ALT "idiot light" on the dash. However, if there is a partial failure in the diode trio (older GM vehicles) the idiot light is lit very dimly, and is hard to see during daylight.

    In the schematic I've posted, the yellow LED is turning off and the green is turning on at 12.7v.
    The threshold for green to red transition is currently (sic) 13.1v.
    Replacing Z2 with a 1N753 6.2v Zener and R4 with a 270 Ohm resistor would change the green-to-red threshold to 14.7v.

    Of course, the schematic was built with "ideal" components. Our OP's mileage may vary.
    [eta]
    I agree, TL431's with trim pots would be a much more flexible design; but they make electronic kits nowadays to be as cheap as possible.

    Sure do miss the Heathkit days. :(
     
    Last edited: Oct 20, 2009
  9. Wendy

    Moderator

    Mar 24, 2008
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    I've never seen the symbol for zener's they show on their schematic. Where was this made, China?
     
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