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Thread: Electrical question

  1. #1
    Old timer craZee's Avatar
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    Default Electrical question

    It seems like something is not right with the charging system on my LS1 swapped Z car. It barely turns over at times but when I put a charger on the battery it reads that it is fully charged.

    I started to check things out last night, suspecting that I would see no increase in the voltage at the battery when the engine was started(meaning no charging). Instead, I found just the opposite. Static voltage was 12.3 volts, when the engine is started the voltage gradually increased all the way up to 15 volts and hovers about 14.8 - 14.9 volts.

    This seems higher than what I am accustomed to. I called the group I got the wiring harness from and they said indeed the LS alternators put out 15 volts and that there should be no need for a regulator of any type between the alternator and the battery.

    Does this sound right to others? I am afraid I am cooking my battery and since it sits right behind the front seats, I really don't want it blowing up.

    craZee

  2. #2
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    Stock battery? What is the cca and amp/hr rating on the battery?

    Is it worse when hot? I've had starters that were going bad and drawing a lot of amps when starting leading one to believe it was a battery issue. Rebuilding the starter was the answer.

    A charging system tester is a great tool in these situations f you have access to one:

    Great deal on OTC Tools 3180 at ToolTopia.com
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  3. #3
    BMW Master bawareca's Avatar
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    In a street fully equipped car with many electrical consumers 15 v from the alternator will result in 14.2-14.7 volts going to the battery.In your car with not much equipment drawing power from the alternator you may see 15 v at the battery terminals.Most modern car's alternators produce 14.5-14.8 volts,15v is not uncommon and may only hurt the long time reliability of the battery,a lil bit.
    From your explanation I would suspect bad connection of the positive cable from battery to starter,ground strap,or too thin of a ground strap installed.Or starter.If you connect jumper directly to the engine(negative) and starter lug(positive) and starter turns Ok that means that the problem is in the cables.

    P.S.You will find out that you are overcooking the battery when you start to smell sulfur aroma,that is a sure sign for overcharging.
    Loose Caboose likes this.

  4. #4
    Old timer craZee's Avatar
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    Thanks for the advice. Yes, very little load on the charging circuit. Fuel pump and ECU is about it. No cooling fan needed unless sitting in grid. I have not smelled anything, but have not intentionally tried to. I am going to see if the battery is hot to touch after a session this weekend. Water level does not seem to change, and I would think it would boil off if overheating. Cable connections are solid and sized correctly.

    craZee

  5. #5
    Senior Member Gian's Avatar
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    Voltage drop test. It's the most comprehensive test you can do for finding problems in the starting and charging systems. You can find bad connections and wires. Load testing helps to.
    You can estimate load tests on the batter by using a DVOM set on voltage and Min/Max turns on. Crank the started and let it run. Checking out you minimum and maximum voltage will tell you approximately load on the battery and if the battery is good. Anything under 10.5 volts-NG
    That's not a Typo, I just can't spell no so well.

  6. #6
    Senior Member fatbillybob's Avatar
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    Your battery is dead or not charging. Put it on a charger and see if it load tests.
    voltchart.gif

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