Charge fault

[stevec5]

My citroen C5 x7 has developed a charging fault - dashboard alarm states; "Battery supply or electrical charging fault" and the battery symbol stays up on the instrument panel. The fault isn't permenant, it can come on at anytime during a run stays on for 10mins or so and then clears! I have checked the alternator belt and clutch pulley and they're ok i.e. not slipping. I stopped the car when the fault came on and checked the battery voltage which was 12.5volts indicating it is an actual fault and not just and indication error. The connections to the alternator are clean (one push on plug for the excitation and a stud for the battery feed). Does anyone have a circuit diagram for this car, or have had a similar fault.
Thanks

[sparksie]

Ok, 12.5 is too low.
Check the voltages at the alternator.
You should have battery voltage at the B+ terminal and slightly higher at the D+, with engine running.
Ignition on, but not running, you should have a low voltage (2ishV) on the D+.
I'm not familiar with your car, but these are basic facts associated with all standard alternators.
Given you only have 2 wires going to the alt, you can be sure you don't have an external reg, or ecu controlled alt.
If you have a higher voltage at the B+ terminal than at the positve battery post, you must have a bad connection in the charging line. This is likely to be a big fuse not correctly seated, or with burned contacts in the fusebox.
Given the intermittent nature, however, my money's on brushes and/or slip rings in the alternator.

[Peter.N.]

You should have around 14.4 v across the battery with the engine running, if much less you have a faulty alternator or a fault as described by sparksie.

Peter

[stevec5]

Ok thanks - I intend to take the alternator off and check the brushes/slip rings - with this being a 2 wire alternator, i assumed the thin wire with the plug connector would be the excitation but when i removed this and started the car with only the battery connected and checked the voltage at the battery - I was getting +14v (obviously when the fault wasn't present) how can the alternator charge without excitation? or is this small wire for something else?

[xf1ref]

I think that the voltage from excitation wire is used only when the engine is started and after the alternator is self-excited. This why at older cars like mine (xantia) the charging light from dashboard goes out.

[Peter.N.]

Yes it was the charging light that supplied the excitation current, so if the bulb went or lead became disconnected - no charge. Check the thin lead connection for 12v with the ignition one.

Peter

[sparksie]

Hi
Firstly, it's not a good idea to disconnect wires from alternators while they're running.
Some depend on the battery presenting a load, for regulation purposes. Other's monitor the D+ terminal voltage.
You could cause a dramatic overvoltage and "spike" the sensitive electronics cars are riddled with nowadays!
However, you may have a self exciting alternator, in which case the thin wire may be the "W" terminal, used to drive the tacho on diesels.
Even a non self exciter may sometimes do so due to residual magnetism in the iron cores.
You can't depend on lack of excitation current to prevent the alternator from working any more, though it used to be common practice to do exactly that with old CAV types. You could remove the alternator load, to save fuel, or increase available power, by switching off the warning light feed.
Can you probe the small terminal with the engine running?
If it's 0.5v higher than battery voltage (hopefully around 14.5 - 15 volts) then it's D+ and is used for excitation.
If its around 7v it's most likely a W, connected to one phase of the alternator, and intended to pulse the tacho.
Of course, while it's not working, none of the above may apply...

[stevec5]

Thanks for that, I'll carry out some tests today. I didn't disconnect the main battery connection, just the small wire and that was before turning the ignition on. But thanks for the advice. My car is a diesel - will the terminals be labelled on the alternator.

[sparksie]

Usually the terminals are labelled.
If it's a Valeo, you might find it confusing, though. Valeo use the same rear bracket for several different alternators, so you may find a lot of markings beside holes in the bracket, that aren't pertinent to your particular alternator.
Sometimes an educated guess is required to figure out which label applies to the terminal you're looking at.
In your case, with only two wires connected (though don't be surprised if you find a third!), it should be relatively easy.
In a conventional setup, you'd expect the main terminal (B+), a smaller terminal (D+, or occasionally L, or WL) and another small terminal (W).
The B+ goes straight to the battery, nowadays via a high value fuse.
D+ is an ignition fed supply, usually via the battery warning light, used to excite the alternator.
W is an AC output, from one of the phases, used to provide pulses for the tacho on a diesel.
There are other configurations, notably on Valeo and Hitachi, which have "battery sensing" and need to be able to sense the voltage at the battery.
Some are isolated return and need a heavy ground lead. Some have wires that are involved with detecting loads and adjusting the regulator before the voltage gets dragged down.
I doubt whether you need to worry about any of these variants, although you are dealing with a Citroen, so....!

[BX]

Sparksie is probably on the ball on this one given that the fault is intermittent. However remember a battery that is failing can soak up a very large charging current without the terminal voltage rising much. On older cars with voltmeters on the dash a low voltage period over a period was as often a warning of battery failure as it was of a fault in the charging system. I got caught out with a Hillman Hunter many years ago. The Lucas ACR 16 was doing its best but couldn't get the voltage to rise over 13V. Turning on the headlamps(twins) and the heated rear window caused the voltage to drop right back to 12V. I fitted a 40Amp Ducellier alternator. Things improved for a while. Then a new battery was tried and all was well. Now I have a DC Current clamp. If the voltage doesn't rise but there is a high charging current bye bye battery.

[djadams]

On a modern diesel like the DW10/12 HDi units the tacho will be "driven" using an engine speed signal over CAN from the ECU - not a single phase AC from the alternator. Am pretty sure that the smart alternator systems also only have two connections - one from the charging system ECU and the other to the battery, so it being a two-wire set up doesn't guarantee it's simple old-school tech. :-/

[sparksie]

Ok, hands up on that one!
Never had any dealings with an ecu controlled alternator, yet!
I've been led to believe they're more complex than standard ones and use the BUS to interact with the ecu, in common with everything else on the car.
I'd have expected a multi-pin connector for this, but maybe my impressions are inaccurate!
A crude, unregulated alternator can relatively easily be made into an intelligent charging system, using a simple PIC controller and a D/A converter to control current to the field. I suppose this may be what modern manufacturers do...?

[djadams]

...I'd have expected a multi-pin connector for this, but maybe my impressions are inaccurate!
A crude, unregulated alternator can relatively easily be made into an intelligent charging system, using a simple PIC controller and a D/A converter to control current to the field. I suppose this may be what modern manufacturers do...?

It caught me out the first time I worked with a smart charging system, too - I expected there to be a multi-pin connector, but I think you're right - the alternator itself needn't be "smart" (it needn't have a controller embedded in it to talk to the CAN bus), but it's field current is controlled by the charging ECU, which talks to everything else via CAN...

[stevec5]

I removed the alternator yesterday and checked the brushes and slip rings (the car has done 87k) the condition of these are pretty good, the clutch pulley is OK as well. Whilst checking the alternator over, I noticed the push on plug connection (single pin) has a track from it built in to the rear plastic cover, so it relies on the plastic cover mounting nut for its connection to the regulator (Valeo CL18), this looked a little corroded, cleaned everything up and reassembled - I have now fitted everything back on the car and i'm crossing my fingers!! Does anybody have a copy of the wiring for the charging circuit for this car - C5 X7 2010 170bhp dw10c engine.

[BX]

I know very little about the operation of the smart charge system. The little I do is on Ford. If the vehicle is not charging or has the no charge warning lamp lit. Unplugging the 3 pin connector causes the alternator to function in the old fashioned way. If the vehicle starts to charge the fault is in the wiring or the pcm. If it doesn't the alternator is faulty. I only used this to get vehicles which were in warranty to limp back to the dealer. On older ones the fault was always in the alternator.