SLA charger from Car socket

Discussion in 'General Electronics Chat' started by Johnr86, Sep 24, 2016.

  1. Johnr86

    Thread Starter New Member

    Sep 24, 2016
    Hi Everyone,

    I'm trying to put together a circuit to charge a 7Ah SLA battery from a car lighter socket.

    I am part of a neighborhood watch group in my country (South Africa). As part of this group we all use flashing lights on our scheduled "patrols". This is a simple strobe type LED light that plugs in the car lighter socket. What I would like to do is use an SLA battery with the light so that when I turn off the engine, the flashing light stays on even with the lighter socket off. I do not want to run off the car battery when the ignition is off.

    Points I would like to achieve:
    • Have the light running when ignition is off
    • Not use the car battery when ignition off
    • Use an SLA battery (7Ah)
    • Charge the SLA battery whilst ignition is on
    • Have the light on whilst charging the SLA battery.
    • Protect the SLA battery to extend its life.
    I have done some searching around and so far I have decided on the simple circuit supplied in the datasheet for the PB137(link) regulator (ST). I am concerned that this simple circuit will not provide necessary protection for the SLA battery to prevent premature "battery death".

    I would appreciate your advice!

    My background:
    Trade Electrician
    Diploma Mechatronic Engineering
    8 years Work experience in Maintenance Department of Factories ranging from Heavy metals to Food processing
    Not much experience on circuits < 220v but I have dabbled.

    Thank you!