Do you want the Road Tax system to change? Do you have thoughts on the potential changes to the Road Tax system? | No thanks
AX charging fault - Darcy Kitchin
Please could I have some advice?

The car is 1994 Citroen AX diesel with 90K miles on it. A few days ago the battery light (comes on with the ignition and goes off when the alternator is charging) failed to light up when starting the car. The alternator had been making growling noises for weeks, in fact since the car went through some flood water a while back. After noticing the lack of battery light, I put a simple voltmeter on the battery; engine off 12.5 volts, during starting drops to 11.5 volts, tickover 12.5 volts, rev the engine to 2500 approx, and there's suddenly 14.5 volts. Moreover there's 14.5 volts when the engine revs fall back to tickover again. I blamed the aternator. Last week the alternator drive belt went, so, noticing some play at the alternator pulley (maybe why it threw the belt), I happily replaced alternator and belt. No growling now, but not charging at tickover either. So, I've spent a happy hour or two on Saturday pulling the instrument panel apart and yes, the battery bulb is not blown. Curses.

Is there another component that controls the battery light and charging? Anyone know where it is? What next?

All comments gratefully received. TIA.
Re: AX charging fault - David Woollard

Are you saying the charge warning lamp doesn't come on when you turn on the ign?

What are your voltages now, static/idle/2500rpm?

Re: AX charging fault - Darcy Kitchin
Light is out all the time, voltages just the same with new alternator.
I'm stumped ...
Re: AX charging fault - John Kenyon
Darcy Kitchin wrote:
> David
> Light is out all the time, voltages just the same with new
> alternator.
> I'm stumped ...

Check the bulb. If I remember correctly the bulb is wired in series
with the field windings of the alternator. When the alternator is
not being driven, the field coils act as a few meters of low resistance wire,
and the bulb lights.

When the alternator is turning then a voltage drop occurs across wire
and the bulb goes out.

If the bulb is duff/missing then there is no supply to the field windings your
alternator won't be generating anything.

(for the uninitiated, winding = coil of wire stationary or moving, forming part of a motor, dynamo or alternator)

Re: AX charging fault - Darcy Kitchin
Thanks for the reply, the bulb is fine.
Swapped it for another working bulb in instrument panel to be sure
Re: AX charging fault - Mike Humpherson
I've had this problem on a vauxhall astra.

When the engine is stopped, current should flow from the battery, through the red lamp on the dashboard, through the alternator field windings and then back to ground through the body of the alternator.

Obviously your problem could be anywhere along that current path.

My problem was caused by a poor earth connection between the alternator and the engine block.

If you remove the wire between the lamp and the alternator and earth it, the lamp should light. It is probably easiest to remove it at the back of the alternator. (Engine OFF for this test!) The result of that test should divide the problem into two.

If the lamp does not light, the fault is between the battery and where you have removed the wire, and if the lamp does light, the fault is between the alternator and ground.

Mike Humpherson.
Re: AX charging fault - Michael
i had a similar problem a few years ago. It was the a bad earth connection between the engine and bodywork. The earth cable was badly corroded under the bolt that connected it to the bodywork.
Re: AX charging fault - Darcy Kitchin
Many thanks to everyone. I'll test the light at the weekend to see if it works by Mike H's method and I'll check the earth again. This was last done in Feb when 2 glow plugs went at once and I had a general tidy up of earth leads.

Ask Honest John Right column

Value my car