Electrical problem on Peugot Boxer 2003 (1 Viewer)

[Laugher]

Hi All My engine battery keeps going flat. I measured the output of the alternator with the engine running and only got battery voltage. I fitted a new alternator, but nothing has changed. Here's the scary bit, with the engine running, I disconnect the negative of the engine battery, leisure battery is already disconnected, and with all the headlights on and four way flashers going, they remain working. So what is keeping these powered up, it must be the alternator right, so why isn't it charging the battery? Oh, I almost forgot, the engine warning light comes on and goes out when started. Help

 

[Clivefog]

Must be wiring, time for the multi meter.

 

[autorouter]

It is a very bad idea to disconnect the battery from the alternator while the engine is running. Manufacturers go to great lengths to avoid this. Unconstrained by the battery load, the voltage can surge to about 60V for several seconds, until the engine stops. If it's a diesel engine, it won't necessarily stop. The electronics is supposed to be able to withstand this voltage surge, but I wouldn't bet the house on it.

You need to check the battery drain, with a meter. A clamp meter with a low DC amps range is ideal for this - no disconnecting necessary. Easier than a standard meter where you have to pull fuses or disconnect wires to measure amps. I'd have suggested a failed alternator diode, but since you put in a new alternator that's unlikely. Except that you disconnected the earth, which might have caused a diode problem.

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[GeoffnDee]

There have been many problems being caused with poor earth lead connections between the engine and body, even when they look ok., It would be worth replacing (or adding another) the engine to body earth lead.

 

[Laugher]

Hi Jockaneezer

Thanks for that, I have a clamp meter so I will check

 

[Laugher]

Hi G

You got it. Cleaned up all the earths, had to cut the earth braid from gearbox as it was so corroded. Charging at 14V now. Thanks for the advise.

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[GeoffnDee]

Great news and thanks for getting back to us and letting us know that a possible cause fixed the problem on this occasion.

 

[Laugher]

Hi G. No possible about it, I only wish I had joined the forum before I bought and replaced the alternator, anyway I have a spare, unless anybody wants to purchase a second hand, perfectly serviceable alternator.