Battery Charging

[Gatts]

Like many other S owners, I have a battery charging problem. My Volt meter always shows between 11 & 12.

I have put on a new heavy duty battery, a new alternator (55 amps), put on 2 additional new earth cables (engine to chasis, and chasis to battery) but the meter still shows only 11 to 12 volts. I know it should be around 13.5 when running.

My lights, indicators, even using my brake lights, cause my meter to drop into the red or dip in time with the winkers!.

I've looked at the wiring diagram and can't see any reason for this "effect".

Is there anything between the alternator and battery which drops the charging voltage to stop the battery from getting over charged when its at peak capacity?

I know some modern cars have this "restrictor" as standard.

Any idea's

Thanks

Paul.

[dern]

I wouldn't trust your volt meter. Before you do anything else get someone with a proper volt meter to check the system as there may be nothing wrong with it. Do you have any other symptoms such as a flat battery?

My indicators make my voltmeter fluctuate. I think it's normal.

Regards,

Mark

[f402mlr]

The simple answer is "they all do that sir", however I had "slow" indicators at one point - MOT fail!. I found that there was a voltage drop at the chassis grounding point at the rear of the NS front wheel arch. This grounds/returns most of the electrics on the car to the chassis and the current is then returned to the battery via the strap at the bottom of the swirl tank. (Electronics lesson - current can't be created or destroyed - it circulates!) May be worth at least giving a spray with WD40, or stripping down and cleaning. See Figure bottom of pg 118 of v1 of Steve's book for a hint at location. Note diagram is schematic, and doesn't show those pesky returns!

David (BSc MIEE)

Edited to say that dern is right, it may be the voltage at the instruments, not at the battery, Get a separate meter on the battery.

>> Edited by f402mlr on Monday 14th October 20:05

[Ballistic Banana]

dern said:
My indicators make my voltmeter fluctuate. I think it's normal.

Regards,

Mark

Yep my old S3 use to do that when the winkers went too.

BB