3 LED volt indicator?

Discussion in 'General Electronics Chat' started by tee2, Dec 15, 2009.

  1. tee2

    Thread Starter Active Member

    Nov 19, 2004
    I know I have seen a circuit that had three LEDs that would light up at different voltages, but can't find one now.

    It is for my motorcycle, I want a green LED to show a good normal voltage, I'm thinking in the 14v range. A yellow one that would be a warning that voltage getting low, high 12v. And red that the voltage is at or below using the starter.

    I'm not sure of the exact voltagebut that shouldn't be hard to find out.

    Any ideas?

  2. SgtWookie


    Jul 17, 2007
    Hi, Todd.
    You're looking for what is called a "window comparator".

    If over 14.5v, the charging system is probably overcharging your battery.
    13.7v to 14.4v is a normal charging range while the engine is running.
    13.3v to 13.7v is a normal "float" or trickle-charge range.
    At about 12.7-12.9v your battery is fully charged.
    Below 12.5v, it needs re-charging. Plate sulphation begins at 12.5v, which kills batteries quickly.
    Below about 12, it's over 50% discharged. You might still be able to start it, but it won't turn over for very long.
  3. VoodooMojo

    Active Member

    Nov 28, 2009
    attached is the datasheet for a LM3914 dot/bar display driver.

    do a google / bing search. you will find hundreds of circuits that may help you.

    With a handy voltage divider circuit and a little calibrating, you can monitor any voltage range your little heart desires.
  4. tee2

    Thread Starter Active Member

    Nov 19, 2004
    Thanks VooDoo,

    I was just looking at a circuit for the LM3914. Looks like it would do what I need, but it looks like you need and adjustable power supply to set it up, which I don't have. I can't think of anyone with one either. :confused:

    Maybe if I get some $$ for Christmas I can get one. Sure would be nice to have.