Dead Alternator On 2.1td

[Russell]

Hi Folks,

After info if anyone has it at their fingertips:
My alternator is not producing any voltage: so I currently (hah!) have parked the car and am charging the battery. With the battery out of the car, I have tested for continuity from the alternator o/p (big wire) to the battery +ve, it seems fine.

From looking at other posts, it seems there should be the battery voltage available on the excitation coils (small wire on the alternator) when the ignition is on, (and a battery hooked up again), and that this feed is fused, and that it is provided post ignition switch. I don't remember seeing the charging light on at all. In fact, where is it on the dash?!

My alternator belt tension has been loose for the last month or so: I've tried adjusting it, but I'm guessing I have to take a wheel off to be able to get at it properly. The belt squeals when it starts, but usually stops squealing by the end of the road as the load drops. Any info about tensioning this would be useful.

So to the questions:
1) Where is the fuse and what is it's number/rating for the alternator feed.?
2) If the diode pack has blown open, I presume I should still see a charging light?
3) It's not unregulated, ie shorted producing too much voltage. The alternator was spinning, and the voltage was barely 12V at the battery when it was last "working".
4) If there is no voltage at the small wire I presume I can short the two alternator connections together to see if the alternator is still working OK.?
5) How do I get the beggar out?

cheers
Russell

[onthecut]

Hi Russell.

You mention not seeing the ignition lamp. If in fact it has only recently disappeared, that may be your issue. I don't know specifically for XMs, but certainly on some makes the lamp is a series part of the excitation circuit and if the bulb blows --- no output. A touch of 12V to the relevant terminal at the alternator should prove it, one way or the other.

Mike.

[xmexclusive]

Hi Russell

It is worth checking if the drive belt is slack enough to slip round a stationary altenator drive cog.
If you can get your hand into touch the altenator drive cog then it will be noticably hot if the drive belt has been slipping.

ONLY DO THIS CHECK WITH THE ENGINE TURNED OFF AND STOPPED OR YOU WILL NOT OWN ENOUGH FINGERS EVEN TO CHANGE FUSES.

First run the engine for a few minutes then turn off and check by feel the cog temperature. It is surprising but possible for the altenator to have enough rotational resistance to not turn with a slack belt.
The belt noise on start up is common and may just be the belt inner surface having picked up a layer of fine metal flakes.
If you do have to change the altenator then be aware that the power varies with XM model (90 or 120 Ah).
I have just changed the altenator on a V6 and it did not turn out to be as difficult as I expected despite being on the front of the engine down behind the radiator. As I remember there is a lot more access space to get at the altenator on a 2.1TD.

Regards

XMexc

[Russell]

Thanks guys for the suggestions.

If the charging bulb or the fuse has blown (which one and where?) is blown on the excitation side, this could cause no O/P it, so I can check for this tonight, and hope it's one or the other...

If the ignition switch is dicky? The starter solenoid circuit wasn't getting enough volts after the ign switch a couple of years ago, so I inserted a relay which has proved to be dead reliable. But if the switch is dying, and this excitation circuit is separately switched from other switched ignition bits. Or if the voltage available is too low to generate any volts, but high enough to hold my starter relay on?? I haven't got a circuit diagram (anyone have a schematic.pdf that could be pm'd?) so this may be rubbish.

The altenator is being driven though the belt is loose, I (very carefully) held a round bit of spanner against the rotating pulley to check.

cheers
Russell

[Peter.N.]

Hi Russel

I would make sure that the alternator belt is tight before you do anything else, as XMexc says, because if the slip for long they get 'polished' and wont grip without a considerable ammount of force applied.

Also as Mike says, the charging lamp is probably in series with the exiter winding, I know it was on the CX, I would think the XM would be the same. Just try connecting the two alternator terminals together, that should start it charging.

Peter.N.

[noz]

Hi Russell,

Can you advise what model/year/RP number you have? If you let me know I'll post a copy of the respective charging circuit.

In all cars the excitation voltage passes through the charging light on the dash. Its in the form of a red picture of a battery if memory serves... The purpose of this arrangement is so that the light extinguishes when the alternator is working and stays lit when its not. This is the tried and tested circuit design for charging and is used all over the world. When the ignition is on but the engine stopped the lamp on the dash has 12v one side and the other is earthed through the primary windings so the lamp lights. When the engine starts and the alternator produces 14v the lamp then sees 14v on both sides so it extinguishes. The voltage being the same on both sides of the lamp means no current flow hence no light.

A break in the charging circuit, by whatever means, should result in the light not coming on at all, in any mode. A blown fuse would do this but the question must be asked - why has the fuse blown?

Cheers

noz

ps
why not stick your car details in your signature? That way, when you're asking a question, we know which model you're talking about.

[Russell]

Hi noz, et al.

Thanks for the circuit offer: that will help immensely.
What's the RP number and where do I find it?

If it helps the VIN is VF7YA3F0008AF0818, sig amended with car details.

Back to the plot: which is thickening, and outside with the car where it is dark and cold.

Battery out:
I tried putting a DVM on the small wire at the alternator (lets call this SW), with the ignition switch on: I got 14.5R to ground, presumably sensible through the alternator winding. However, I got 12R to the battery +ve lead connection at the alternator (call this BW, big wire). I expected the reading to be 0R, as the ignition should switch battery +ve(BW) to to the excitation coil on the alternator (SW). But maybe it would be supplied via a relay, so with no battery in I didn't know what to make of that reading, apart from a high resistance.

Battery in: sparks. OK turn off the ignition and try again! Connect battery, turn on ignition, and measure 2V at SW to ground, and roughly 10V between BW and SW. So I have a high resistance connection. Shorting them together? I didn't do it. The SW post is sunk inside what looks like a castellated nut, which connects directly to the alternator housing, unless it's insulated in some way I couldn't spot. The slightest slip with holding a wire on the SW post will short battery voltage to the chassis, and it was dark and cold and the motor would need to be turning, and I needed to take a voltage reading while holding a torch with my teeth! I'll wait for daylight at the very least.

Someone please tell me about this SW terminal post! I can't see what is going on, but I'm guessing there is an insulated stud in the post with a nut that holds the small wire which is probably terminated in a ring tag over the post, and insulated right up to ring tag to avoid shorting it on the alternator/chassis. Can someone confirm this is the arrangement, and ideally tell me it's an M4 or M3 nut on the post I can't see! I think there will be blind unscrewing at some point soon, it's just handy if I'm waving the right tool at it.

The battery charge light was working in the car with ignition on. I forgot to look at it when the engine was running. Battery voltage was steady at 12.5V, but I had charged it for some time, so the alternator wasn't providing anything, proved by revving the engine slightly: no change whatsoever.

Tommorrow is another day. Except it's today already.

cheers
Russell

[onthecut]

Hi Russell

You do know, deep down, don't you, that you're going to wind up taking the alternator off and having it mended at the end of this. It's Sod's Law and works every time !!!!!!!!!! All I would suggest is if you have a good local repairer, give them a whirl. I've seen some very silly alternator prices, when generally the fault can be fixed with new brushes and a regulator at a fraction of the price of a 'rebuit' unit.

Mike.

[xmexclusive]

Hi Russell

On the altenators I was sorting through to swap the one on the V6 the big castellated block around the connection nuts was a black plastic insulator. I managed to do the swap with everything live.

Regards

XMexc

[xmexclusive]

Hi Russell

ORG or RPN Number are different names for the same 4 digit number that Citroen paint between the hinges on the front passenger door pillar of cars.
It decodes to give day of manufacture.

Regards

XMexc

[xmexclusive]

Hi Russell

Have just noticed you asked about altenator nut sizes.
I used a 13mm socket on the large lead and a 8mm socket on the small one.

Regards

XMexc

[noz]

Hi Russel,

This is the closest circuit diagram I can find for your model and year. The salient points (ie the fuse and the dash light) are the same for all diagrams.

When testing any part of a circuit make sure that the lead of the multimeter is touching the part which is furthest down the circuit. What I mean by that is don't assume just because voltage appears at one end of a cable that it must appear at the other. You could have a break in between. In particular, check for voltage at the actual terminal on the alternator not just on the spade connector at the end of the cable. Joints are your most probable location for faults.

Hope this helps.

Cheers

noz

This post has been edited by noz on December 14, 2006 09:06 am

[Russell]

Hi Folks,

It's a poor connection in the feed to the excitation coil, possibly a broken wire.

To fix it I want to supply 12V to the alternator coil connection using a relay with the coil operated by a local +12V ignition switched feed. I'll be loading this feed with a massive 50mA or so, but would still prefer it to be something reasonably beefy.

Any suggestions for a good source of ignition switched +12V in the engine bay.?
Maybe the feed itself might be able to source enough to turn a relay on, but I don't like relying on something broken already.

The circuit diag doesn't show any intermediate connection, but does anyone know if this connection plugs together to the loom from the dashboard somewhere in the engine bay, as I would have thought this quite likely? Many thanks.

cheers
Russell

<background>
All went quiet for a while there. Thanks Noz for the circuit diagram, and XMerc for the the nut sizes. I could see in the daylight today that the small wire (SW) connection is insulated with black plastic: it's amazing how metallic that appeared the other night with a torch. 8mm was on the money too, XMerc. Good job I have another car at the moment.

Today I put a charged battery in, turned ignition on, battery light glows on dash. Checked voltage at SW, it was 4V. Wiggled wires, got a max of 7V. Disconnected the feed rose to 11.3V, but it just can't supply any juice at all.

The high resistance (poor connection) lead pretty much proved, I shorted the SW post to +12V. In the car with ignition off the battery light was glowing, which makes sense, turned on ignition (it went out- still makes sense) started and sure enough alternator working OK, voltage rising at Battery to 14.2V. Revving the engine, voltage solid at 14.2V so regulator OK.

So that's the problem diagnosed: I have a poor connection between the SW on the alternator and the bulb connection on the dash, possibly a broken wire.

Now on Noz's diagram there is also a feed from a relay coil (Part 848) which is the engine running information relay. Can anyone tell me where this lives? It is probably also under the dash near the battery light and other tell tales, but you never know your luck.

Now I'm guessing that getting at the dashboard end of the wiring is not especially easy. And being a philistine, I can just run another wire to the alternator coil from any suitable ignition switched feed via a relay without it worrying me too much.
</background>