355 - How to measure battery voltage? | FerrariChat

355 How to measure battery voltage?

Discussion in '348/355' started by evo11, Jan 7, 2022.

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  1. evo11

    evo11 Karting

    Sep 21, 2020
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    K
    Gentlemen,

    I wish you all the best in the new year and that your Ferraris never let you down

    Can you tell me how to measure the battery voltage in f355 without removing the wheel arch, the battery is always disconnected with the knob and I do not want to turn it on because the immobilizer control unit is disconnected due to programming.

    In the future, I want to lead the plus cable to the top so that I can charge the battery at any time

    Thanks K
     
  2. greyboxer

    greyboxer F1 World Champ

    Dec 8, 2004
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    Jimmie
    I may be wrong but the 355 has a charging stud on the top of the frame in the engine bay which I think is connected even if disconnect off so logically you should also be able to measure the voltage between the stud & earth (see L8 owners manual)
     
  3. evo11

    evo11 Karting

    Sep 21, 2020
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    Thanks for ultra fast reply :)
    unfortunately I don't have manual near :(
     
  4. Mike Morrissey

    Mike Morrissey Formula 3
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  5. Qavion

    Qavion F1 World Champ
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    The positive stud in the engine bay is connected to the battery positive, but there is no negative. If the cutout is used, you isolate the battery negative lead from the chassis. You cannot charge or check the battery from the engine bay.
     
  6. greyboxer

    greyboxer F1 World Champ

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    'I may be wrong' - thanks correction !
     
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  7. evo11

    evo11 Karting

    Sep 21, 2020
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    So no chance that I could check voltage operating under front hood?
     
  8. evo11

    evo11 Karting

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  9. Qavion

    Qavion F1 World Champ
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    That gives me an idea. In the case where you couldn’t access the CTEK pigtail, and since you also have access to the battery cutoff switch, it may be possible to stick one of the voltmeter probes on the battery side of the cutoff switch and the other voltmeter probe on one of the fuses in the frunk which is hooked up directly to the battery.
     
  10. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
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    There is a stud on the subframe near the + terminal of the right hand side 12V connection. That is the Neg stud.
     
  11. Qavion

    Qavion F1 World Champ
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    Do you mean in the engine bay?

    That won't work if your cutout switch is in cutout and you're measuring across here:

    Image Unavailable, Please Login
     
  12. Ferrari Fanatic

    Ferrari Fanatic Formula 3

    Apr 2, 2003
    1,317
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    Battery voltage is slightly meaningless, until you put a load on the battery and then see how far it drops. Are you trouble shooting an issue. Not being inflammatory just curious.
     
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  13. Qavion

    Qavion F1 World Champ
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  14. evo11

    evo11 Karting

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    Battery voltage is the basic parameter that clearly defines whether there is a problem or not. I didn't start the engine for 4 months so I was curious about the condition of the battery
     
  15. taz355

    taz355 F1 Veteran
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    Feb 18, 2008
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    Mine is not like that it’s a 99
    If disconnect is off no connection to battery from the back
     
  16. taz355

    taz355 F1 Veteran
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    If you could do this that would work
    Mine cuts off the positive
     
  17. Qavion

    Qavion F1 World Champ
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    Is your battery fitted back to front?
     
  18. taz355

    taz355 F1 Veteran
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    Not sure what you mean Ian
     
  19. taz355

    taz355 F1 Veteran
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    My batt is in the front pass side if that’s what you mean
     
  20. taz355

    taz355 F1 Veteran
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    If you mean orientation in the front it is the only way it could be mounted due to length of wires
     
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  21. Qavion

    Qavion F1 World Champ
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    Your cutoff switch is attached to the positive terminal of the battery?

    (EDIT)

    Ah, makes sense
     
  22. taz355

    taz355 F1 Veteran
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    My charger is hooked in back and will not charge if cutoff is active
     
  23. taz355

    taz355 F1 Veteran
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    I think so
    Would that be wrong according to the wsm
     
  24. Qavion

    Qavion F1 World Champ
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    Correct, but the cutoff switch is still attached to the negative terminal of the battery.

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    Your engine bay charger is attached to both the positive terminal and the chassis. When the battery switch is in cutoff, the chassis is no longer attached to the battery, so the charger will not work. The positive wire remains attached.
     
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  25. taz355

    taz355 F1 Veteran
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    Ok makes sense
    When we do this on our heavy equipment I think we always cut the positive but I can not remember the logic. I incorrectly assumed my car was the same
    Thanks for the correction
     

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