Ammeter Question | FerrariChat

Ammeter Question

Discussion in 'Technical Q&A' started by Ken, Jul 1, 2005.

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  1. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
    Full Name:
    Kenneth
    Please excuse me if this is off topic as I have a Lotus, but I have a question about my alternator/ammeter. I just had the alternator rebuilt as my car was starting to run off the battery. The VR was changed as well. As I rev into the upper band my ammeter is reading +35 Amps! It NEVER did that; would always be at +5 or so. At idle it does read +5. So, is my battery shot and needs to be charged, or is my VR no good and I'm cooking the battery?

    So far all anyone says is "check it out" but I need the car tonight and can't. I don't want to blow the thing up however!

    Thanks!

    Ken
     
  2. BULL RUN

    BULL RUN Formula 3

    Dec 18, 2004
    1,684
    It would not be abnormal for the ammeter to register a higher amperage reading for a short time since the alternator was undercharging the battery for a while. However it should go back to the 5 amp range after driving a few miles. a digital voltmeter accross the battery should read not more than 14.5 volts or so at any RPM, if it does it's cooking the battery.
     
  3. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
    Full Name:
    Kenneth
    I know it's dangerous to make assumptions, but my battery is only 2 years old, and I didn't drive on the battery for more than 1-2 miles if that. The fault was intermittant. I have driven less than a mile since the R&R so if the battery IS in need of a charge I haven't gone far enough obviously. Frankly, I was afraid of cooking it which is why I'm asking.

    So my question is: If I put some miles on it and see if the needle returns to it's normal neutral range am I risking anything by doing this? I'll do laps around the block...

    Thanks!!
    Ken
     
  4. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
    Full Name:
    Kenneth

    Another comment I just got: "Your field coil is shorting to the ground; you will fry your battery!" I think I better take it all apart again!

    Ken
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,931
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Measure the voltage across the battery during the +35A condition as Italiacars suggested -- if it's exceeding the ~14.7V with increasing RPM then you can declare "cooking" (and have no recourse but to take it apart again), but if no trouble found (and smoke isn't leaking out somewhere;)), why not try an operational test for a few more minutes stationary?
     
  6. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
    Full Name:
    Kenneth
    Good idea. I need to buy a voltmeter....I'm embarrassed to say I don't have one! I do think I need to take it apart though....just a hunch which is a bad way to fix cars!

    Ken
     

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