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12V DC voltage stabilizer

Discussion in 'Electronic Basics' started by ZhangLu, Nov 8, 2005.

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  1. ZhangLu

    ZhangLu Guest

    I'm looking for a circuit diagram for 12V DC voltage stabilizer for my car.

    I found that every time when I start my car, the starter motor will draw so
    much current that cause the voltage over the ignition coil to drop

    Most circuits I found need higher input voltage to produce a lower stable
    voltage, but the only voltage source in a car is from the battery. So it's a
    12V-12V DC voltage stabilizer that I'm looking for. Any recommendation?

  2. Pooh Bear

    Pooh Bear Guest

    The battery needs replacing.

  3. PeteS

    PeteS Guest

    ISO 7637-1 (12V vehicles) specifies the voltage droops you may expect
    to encounter during engine crank (amongst other things)

    Although I agree with Graham your battery may need replacing, during
    cranking the battery feed may droop to as low as 5V, then raise to
    between 6V and 9.5V once the starter motor is running. Once the starter
    motor is disengaged, things should recover to normal.

    As the only feed during that time is the battery, you would need to
    have a circuit that can take 5V ->14V in and produce your clean power
    for whatever it is you are trying to operate. (Think SEPIC converter).


  4. Rich Grise

    Rich Grise Guest

    Yeah, and the additional current drain on the battery will drag it down
    even more.

    Does the car not start reliably? They're generally engineered to take
    all of those factors into account.

    IOW, if it ain't broke, don't fix it. :)

    Good Luck!
  5. ZhangLu

    ZhangLu Guest

    The battery is a new one. The car, it's an antique car, 1963 moris mini. I
    find it hard to get started at times. Anyway, thanks for all the advice.

  6. ehsjr

    ehsjr Guest

    Look for rust/corrosion on connections in the
    coil circuit, particularly the grounding cable
    from the battery to the engine block.

  7. JeB

    JeB Guest

    I might build or buy a Capacative Discharge Ignition for it ...
    although those older Brit cars are famous for electrical problems.
  8. Pooh Bear

    Pooh Bear Guest


    The battery in that may be slightly undersized by today's standards.

  9. Rich Grise

    Rich Grise Guest

    ANTIQUE????!?!?!??!?!!!! 1963??!?!?!??!??

    Hey, that's when my family got our first convertible! A Ford Galaxie
    500, in "Anniversary Gold", with a red top and red interior. That was
    the one I learned to wreck cars in. ;-p

    Anyhoo, I'm the one who said "If it ain't broke, don't fix it," but
    since you've admitted it's a Brit car, here's what I'd do: First,
    as someone else has posted, make sure you have very good electrical
    contacts, both at the battery posts and at the lugs where the
    cables bolt to the frame/engine block and to the starter or
    solenoid. Clean them very aggressively with a wire brush, but
    avoid chemicals. Don't grease them right away - bolt them up,
    and grease them all around. I don't know what kind of battery
    terminals you have, but I have had the kind with the vertical
    lead posts, and the lead lugs that always get torn up when
    people loosen them with pliers and stuff. Well, I got a post/
    lug cleaner at the auto parts for about two bucks - it was
    two very stiff wire brushes: one to go inside the lug, and
    one to go around the post. I also got new cables, with new
    leaden lugs, and stuck washers under the bolt head and nut
    so I wouldn't tear up the lug when I had to loosen them.

    Which, as it turns out, I didn't have to do very often. ;-)

    Now, I have the kind with side terminals, and I just keep the
    mating surfaces clean and shiny, and keep a 7MM wrench in its
    own special place in the trunk. :)

    Good Luck!
  10. Michael Gray

    Michael Gray Guest

    Most older cars use a simple series resistor to the coil which is
    shorted out when cranking.
    Easy to implement and very reliable.
  11. Michael Gray

    Michael Gray Guest

    "Lucas", Prince of Darkness.
  12. neon


    Oct 21, 2006
    A car battery running a 12 v dc amplifier cannot drain the battery not for at least a day if the car is not running. You do not understand when a car is started the battery see practicaly a very low resistance to spin the starter and flywheels and and also the ignition coil. So a 12v [never is 12v] will dip to 8v to even 6v until the car starts. Once started you may remove the battery it will run fine on the generator. The battery is just there to start up the car after that the generator takes over charge the battery for next time and that is the idea.
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