CPH

Alternator problems, only 12.6V

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Fiesta MK7 1.6 diesel 2010.

After having a flat battery a few times i had a new battery fitted. After 10 days with the new battery i had a flat battery again. Took it to my local garage and they diagnosed faulty alternator and replaced the alternator. Yes within a week............ another flat battery. Alternator checked at tick over 12.6V dropping to 12.3V when electrical items were switched on and the battery was down from 12.6V new to 12.1V. Obviously the alternator wasn't charging the battery. Alternator was replaced under warranty and the replacement still only giving 12.6V. Auto electrician and garage pointed at the wrong type of battery fitted (although it turned out to be the correct silver calcium type battery) so had that replaced under warranty and still only 12.6V. The new battery was 12.65V when fitted, dropping to 12.03V after one week. I believe my car was fitted with the smart alternator which varies the power output to suit.

Ford have also had the car on diagnostics and could find no fault. All earthing points were good etc etc

The car has been jump started on numerous occasions when the battery was flat.

Now i'm at a loss as to why my alternator isn't charging the battery. Two alternators and two batteries, any ideas? 

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3 hours ago, CPH said:

Now i'm at a loss as to why my alternator isn't charging the battery. Two alternators and two batteries, any ideas? 

There is a small connector on the alternator that goes to the ECU. It may be a 3 pin type for the older PWM style of charge control, or a 2 pin or 1 pin connector for the newer LIN bus control.

I would start by unplugging this connector. With it removed, the alternator should revert to a basic fixed voltage output, in the range 13.6 to 14.4 volts.

The main areas remaining are the control wire from ECU to alternator, or something making the ECU think the battery is fully charged. Does the system have one of those battery monitoring sensors mounted on the battery negative terminal? If faulty it could be telling the ECU that the battery voltage is too high. Or even it may need a reset via the diagnostics after the changes.

The battery needs about 13.6v to maintain charge, and well over 14v to get it up to full charge. A cheap voltage monitor that plugs in to the cigar socket can help to verify what voltage it gets up to while driving. If you have access to a laptop, Forscan can monitor the charging system also while driving. There are versions for smart phones etc as well.

The dealer and others who have looked at it so far seem a bit incompetent if they think it is the wrong type of battery, especially as it wasn't. The usual problem with the wrong battery type is that its life gets shortened by the higher voltage put out by the Ford charge system, not that it makes the voltage stay low.

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Time to find someone who can do proper diagnostics, with the use of an oscilloscope. Throwing parts at it is not going to fix it.

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Might there be a drain somewhere while stopped?

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