1. Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.
    Dismiss Notice

12v Starter Slower To Crank

Discussion in 'Early CJ5 and CJ6 Tech' started by aekdbbop, Sep 1, 2016.

  1. aekdbbop

    aekdbbop Member

    So I had a 6v starter on a 12v system. Foot pedal starter style.

    Now I have a12v starter I installed. Engine is cranking slower and I can tell it's having a harder time getting started.

    What can I do? More CCA?
     
    aekdbbop, Sep 1, 2016
    #1
  2. PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    12 Volt should require half as many amps. V=IR. It will crank slower, because the six volt unit was being over-revved on twelve volts.

    Otherwise, check and clean all the connections, including the switch, ground to the frame, etc. Is the foot pedal link and starter switch button adjusted correctly to give firm contact with the new starter?

    I'd try also the starter with a jumper direct from the battery, to be sure the starter itself is okay.
     
    Last edited: Sep 1, 2016
    PeteL, Sep 1, 2016
    #2
  3. aekdbbop

    aekdbbop Member

    We're no longer using the foot switch.. keyed starter now.
     
    aekdbbop, Sep 2, 2016
    #3
  4. ETZFAM

    ETZFAM FLATIES & ROUND FENDERS, SOME EVEN RUN

    Did you go with the newer gear reduction starter?
    They are the cat's meow?
    If everything is clean, good cables, should start right up?
    As PeteL said needs have the amps because of the higher voltage, you really can use a 6 volt starter and then put 12 volts to it and work great as long as the brushes are good, etc?
    I also would check it with a jumper to see if it is the same, sounds like the new starter is not good?
     
    ETZFAM, Sep 2, 2016
    #4
  5. Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Actually I've measured draws on both 6 & 12 volt starters running on 12 volts- draw is effectively the same- ~ 165-180 amps.

    This makes sense if you think about it as it's the same power required to turn over the engine (hp = watts = volts x amps)

    I've found that a fresh 6 volt starter will spin a bit faster than a tired 12 volt but it's probably got more to do with brush/commutator condition than anything else.

    Check your connections/solenoid, sounds to me like that's where your issue is.

    H.
     
    Howard Eisenhauer, Sep 2, 2016
    #5
  6. Glenn

    Glenn Kinda grumpy old man Staff Member

    Does it act like it's really having a tough time or just spinning slower?
     
    Glenn, Sep 2, 2016
    #6
  7. Glenn

    Glenn Kinda grumpy old man Staff Member

    Well, this just threw my understanding of voltage and amps straight out the window. Darn! :)
     
    Glenn, Sep 2, 2016
    #7
  8. aekdbbop

    aekdbbop Member

    just slower. I can here a difference in the pitch.
     
    aekdbbop, Sep 2, 2016
    #8
  9. PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Well, this just threw my understanding of voltage and amps straight out the window."


    Throws my understanding of math right out the window, too. Although a very small window would be adequate.

    Howard, I believe your hands-on finding, but surely your electrical formula means twice the volts equals half the amps, for the same HP/watts?
     
    PeteL, Sep 2, 2016
    #9
  10. aekdbbop

    aekdbbop Member

    [​IMG]
     
    aekdbbop, Sep 2, 2016
    #10
    eti engineer likes this.
  11. Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    I was surprised by the results as well but they is what they is.

    Also, following conventional thinking on this would mean applying 12 volts to a six volt starter would mean four times as much energy applied to the starter which you would think would spin the engine four times as fast but of course this doesn't happen- the starters will not spin faster that a certain RPM (no load speed) & will draw more amps as the load increases to try & maintain that speed. Also I suspect that engine drag isn't straight line torque vs. RPM either- probably a curve there of some sort.

    I'm guessing that the 6 & 12 v starters have a similar no-load speed & of course engine resistance will be the same in either case so the differences between them will not be as great as we all thought.

    H.
     
    Howard Eisenhauer, Sep 2, 2016
    #11
  12. Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Actually thinking this through I suspect my theory is half assed ^H^H^H^H ^H^H^H^H^H wrong but they still seem to draw about the same amount of juice. :rolleyes:

    H.
     
    Howard Eisenhauer, Sep 2, 2016
    #12
  13. aallison

    aallison 74 cj6, 76 cj5. Has anyone seen my screwdriver?

    Could it be wired incorrectly?
     
    aallison, Sep 2, 2016
    #13
  14. eti engineer

    eti engineer Member

    Mine too, and I am a high voltage test engineer, but then again, that is AC volts (lol)
    Do me a favor and tell me what the voltage is that accompanies that current draw when you roll your starter...

    If you are drawing an average of 170 amps when you hit the starter at 12 volts, which actually drops to around 10 volts max on a good battery, you are drawing a total of 1700 volt-amperes or higher, if your battery voltage stays up, which is the same value as watts in DC circuits. This sounds awfully high for a 12 volt starter motor. I don't know what the hp rating for a standard starter motor is or I could tell you what your battery voltage is when your cranking. For example, if your starter motor is 1 hp, you would be dropping your battery voltage to around 4 volts if you are drawing this kind of amperage. When I am starting my jeep, my voltage never even hits 10 volts when cranking, and my current is much, much lower than that... 1 hp = 748 watts (volt-amperes)
     
    eti engineer, Sep 3, 2016
    #14
  15. Chilly

    Chilly Active Member

    A stalled motor with 12v battery will draw more current than a free-turning motor with 12v battery. Counter-electromotive force (CEMF), which is sometimes called generator action in a motor. It's what causes a long piece of copper wire (windings) from being a dead-short. But a stalled motor has no CEMF so it does become nothing but a short-ciucuited ball of copper wire. That's why a stalled motor burns up.

    That's why the Ohms Law doesnt exactly line up when there are motors involved.

    And as was already suggested, there is voltage droop in the battery due to internal resistance.
     
    Chilly, Sep 3, 2016
    #15