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    Charging System Questions? # Archived Message

    Posted by Dave Hill on August 14, 2009, 10:10 pm

    Evening all.

    In the last few months I have seen a few motors that have left me a little undecided about whether or not the alternator is faulty. In all examples I have seen good charge rate (measuring volts at the battery), but at idle, with lots of heavy consumers turned on, the battery voltage can be seen to drop to around 12 volts (sometimes less). I have seen this on a few Fords, a Range Rover P38 2.5 TD & now a Isuzu Rodeo TD. I remember a guy telling me a while ago about a problem with Nisaan Navara's struggling to maintain a charge when the glow plugs are on.

    I think it is fair to say that when a Ford Focus has the heater fan on full, the front & rear heated screen, the headlights etc etc that there must be some serious electrical demand on the alternator. I see quite a few diesel motors that only do "the school run" & the battery will run down often (particularly in the winter months). I wonder what test methods the more professional "Sparkies" out there use, to make a decision?

    Here is a capture I made today, from the Izuzu I mentioned. The alternator was replaced with a genuine unit (at the request of the customer :shock: ) & he later mentioned that he was still suspicious about the charge rate.

    I am scoping Glow plug current (Blue) & Alternator output (Red) & Battery voltage (Green) Here is the animated capture...............



    Sorry it this is too heavy for a Friday night. :?

    Cheers all

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