Charging issues

[PaulF2.5TDi]

I've posted this elsewhere, but

I am having issues with the charging system on the Avant (2.5TDi Q) that appear to have been ongoing for a while!

When I start the car, the battery voltage stabilises at about 12v(reading the dashboard ammeter) for a couple of seconds, and then comes up to 14v. The time it takes to come up varies, from a couple of second to a few minutes. If the voltage was below normal charge rate,and heaters,lights etc were on, the lights dim and voltage drops. After the voltage has stabilised at 14-ish, no problem.

As I had starting issues, I diagnosed a duff battery and got the worlds biggest tractor battery shoehorned in. This helped the starting, but no effect on the charging.

I then decided it was the alternator, and changed it for a second hand unit. This appeared to improve things, but not by much.

Today, MrsPaulF called to say the charging light was on, with the voltage gauge at 12v after stopping to fill up. Whilst talking to her (helping her to reduce the load) the light went out and the voltage jumped up to 14v. After about 15 minutes of driving, it went down again and stayed there.

It seems to me as if there is a Generator Control Unit playing up, but as the car doesn't have one, I'm a little stuck.
Is there a relay that the alternator charges through? (I'm thinking if so, it could be sticking) The other is earth straps - I did try jump leads from the engine to the negative terminal a while back, just in case the engine earth was playing up - no joy.

Any thoughts would be welcome.

I'm also having trouble with my wiring diagrams, so can anybody with a charging circuit diagram post it for me please?

[Jo Illingworth]

I'm watching this with interest, I'm having the self same at the mo on a passat, new alternator but no charge going into the battery, do they need programming to tell them the new alternator is on?

[PaulF2.5TDi]

When I put the second-hand unit on, there was no programming required.

My best guess at the moment is a sticky relay of some sort - I have no idea where, though!

[adamss24]

No relay as such, could be worn brushes or a bad diode in the rectifier pack !

[PaulF2.5TDi]

Thanks Chris, the problem is it was the same with two alternators.

Rectifier diodes seemed a good bet originally due to the fact it got worse with the cold, but after changing it a good few months back (thanks again for the ident help elsewhere!) with no real change I felt it was something else at fault. A plug full of oil could be a culprit to check.....

The reason I keep banging on about GCUs and relays is that it does seem to 'come online' in a very specific manner. The saloon does too, but within a few seconds every time.
You start the car, the voltage drops to 10-11volts (heavy load, ok), the voltage comes up to 12v (battery recovering) a wait of a few seconds, then up to 13.8-14.2 as prescribed (charging online).
The Avant seems to fall down on the last step for a variable amount of time.

[ametlib]

Hi PaulF,
I,m afraid my diagram was rubbish too as both connections was redirected to the ECU. The D+ is for sure going to the ECU and the thick cable is linked to the battery( via the starter) but the 3rd wire I would expect to be going
to the charging light. In the old days (and I guess nothing have changed;)) the little current going through the charging light was necessary to make the alternater start loading, at first when the dc-alternaters was replaced by the ac-alternators
with diodes, a faulty light bulb(charging light) would strand you. To avoid that problem the manufacturers connected a resistor in paralell to the charging light bulb....
A faulty diode would make your lights blinking, but the voltage would still be 14 v. Faulty brushes would make this fault, but my guess (since you have had 2 alternaters doeing the same thing) something wrong with the wireing ( or voltage)
from the charging light

[PaulF2.5TDi]

Thanks, Amelib.
I now have got my diagram working - sort of. You are correct. One lead is to the battery, one goes to the dashboard and one to the diesel pump ECU.
VCDS allows me to measure the injection pump voltage, and the engine ECU (battery) voltage.
There was a discrepancy of about 0.3v. This suggests there may be earth issues (IP ECU is bolted to the engine, as is the alternator).
These issues would be worse under heavy load (Ask Mr Ohms - higher A for the same R = bigger V drop)

That explains the voltage discrepancy, but not the 'coming online'.
I tried running the car today after spending hours getting a diagram, and the charge light was on with the voltmeter reading about 12v. Checking with VCDS showed about 12 at the engine ECU (battery) The IP voltage was about the same. This implies the alternator was not charging.

As you said, often the charging light current energises the field windings, but if the light was on, I would expect current to be flowing through the winding. Once energised, the field should be self-sustaining.
(I have to be careful as in my professional life things are slightly different and I can get confused at home!)
It is always possible I have a second broken unit.

I didn't do much more today as the weather was truly awful, but will try again tomorrow!

[ametlib]

Part 2:D . I see that you have a good grip of how theese things work, but remember, we are not talking lightbulbs anymore, but more like LED's and electronics ( dash insert)
Here is what I would have done it.
Open the wiring loom that goes over the right side engine rocker cover ( in front of the oil dipstick) and find the blue/black wire. Done by the book you should now measure the voltage on this cable, but as we dont know the resistance
neighter in the dash insert or in the alternater voltage regulator,we wouln't know exactly what reading to expect, so I would go for a direct " headshot" here. Solder a 50 ohm resistor to a wire and connect it to the blue/black (check in the wiring diagram that it's the right color coding)
the other end of the wire to battery +. If the alternater doesn't start loading, the brushes are faulty. If the alternater works with this setup (and I guess it will) your fault is in the wireing or the dash insert...

[ametlib]

BTW The "coming on" issue can mean that the "rest magnetism" in the alternator steel core is big enough to make it start loading without any "start current" from the dash insert. The voltage differences you measured I would
blaim the wiring for, and I don't believe that it has anything to do with your alternater fault.

[PaulF2.5TDi]

'Flashing the Field" - it's been a while since I've done that!

However, I could also try measuring my other car for a reading by unplugging the connector at the alternator, switching on the ignition and reading the voltage (referenced to battery).
You are also correct, I think, about the bulb/led analogy. The big issue is much less current used, and often direct readings are impossible due to transistor switching. I still have Lucas ACR books, and only last year managed to set up a Lucas Dynamo control unit for my tractor, so I know the old ways!

The more I think about it, the more I think you are correct and field current is the culprit in some manner.
I have leaks on this engine, and I bet I will find the plug at the back of the alternator is full of oil. (if you only knew my real life, and how often I solve faults by cleaning oil from the connector plug!!)
The oil will disrupt the field current, thereby preventing the alternator 'coming online'.

[PaulF2.5TDi]

BTW The "coming on" issue can mean that the "rest magnetism" in the alternator steel core is big enough to make it start loading without any "start current" from the dash insert.

I did wonder about residual magnetism - but again, without going into the books for Valeo, I was unsure on the set up. I have dealt with contactor dynamo boxes, Permanent Magnet Alternator (PMA) brushless DC, carbon pile regulators, electronic control etc!

[PaulF2.5TDi]

Ok, an update so far...

I ran the car this morning, and the charge light was on. It went off after a short while and some revving.
I left the car running, to charge the battery, whilst I went to make some measurements. The light came on during this time.

I decided to remove the alternator and check the brushes etc.
As it is truly crap Aberdeenshire weather here, it took a while, but it looks like the slip ring is heavily contaminated. (One of them is black, not shiny copper)

As I still have the original alternator, I decided to have a look at it too.
The slip ring was not contaminated.

However, both units had worn brushes - almost to the limit - and the slip rings are also worn. I will fit a new brush block/regulator to the best unit for now. This should last a year or so whilst I decide what the plan is.

I'll update how it goes over the weekend once I get the brush kit.

[ametlib]

Yes, worn brushes for sure can make this fault and when they become to short they start to burn the slip rings, a mystery though that your original alternator had good slip rings ?
By just replacing the regulator ( brushes) you may have it working a year or two ( if that's the only fault;)) but if you have access to a lathe you can make them good as new.
It's my experience that it doesn't matter if the slip rings diameter is reduced by a half to one mm. I have a minilathe (chester DB8V) and it's just a wonderful little machine for such small jobs.

[PaulF2.5TDi]

The old alternator (which I kept) had very worn slip rings - about 1-2mm down!
The brushes were not at their limit, but were worn.

Unfortunately no lathe, but I may be able to turn them down another way.

The recent alternator slip rings were less worn (only been going up my mile long dusty dirt track for a year, the old one was on longer) but the brushes were more worn - at their limit. As you say, this looks like it caused arcing, burning the rings.

[spartacus 68]

The old alternator (which I kept) had very worn slip rings - about 1-2mm down!
The brushes were not at their limit, but were worn.

Unfortunately no lathe, but I may be able to turn them down another way.

The recent alternator slip rings were less worn (only been going up my mile long dusty dirt track for a year, the old one was on longer) but the brushes were more worn - at their limit. As you say, this looks like it caused arcing, burning the rings.

How much is a new OE alternator Paul... or is it a case of 'don't even ask?'

Just stripped out an electric power steering pump on a 51 plate Mini Cooper and the similarities are almost the same, worn bushes and contact bearing on the armature. You could probably replace the carbon brushes but if but if the slip rings are worn, then simply replace. You know it makes sense, otherwise its only a matter of time.

[PaulF2.5TDi]

How much is a new OE alternator Paul... or is it a case of 'don't even ask?'

Just stripped out an electric power steering pump on a 51 plate Mini Cooper and the similarities are almost the same, worn bushes and contact bearing on the armature. You could probably replace the carbon brushes but if but if the slip rings are worn, then simply replace. You know it makes sense, otherwise its only a matter of time.

About £130 - not terrible, but the brush and regulator pack is about £30 (both from Turriff Auto Electrics), so a big difference. I can also get the pack Saturday, whereas it's Monday for the unit and I'm back on shift Monday so we need both cars then.
I would expect to get a couple of years from it - and I don't know if the car will last much longer than that!
I can get the rotating assembly, including slip rings and bearings for £44, but I think I'll just turn down the best of the two I have with a motor and file/glasspaper.

My problem with any rotating component is 'stew' from the track getting in and forming an abrasive paste in bearings and slip rings/commutators, as well as destroying filters, locks and electrical contacts.

You are correct in what you say, But..........

[PaulF2.5TDi]

An update :-

I got the brush/regulator pack on saturday and picked the alternator with the least wear on the slip rings. I used a star bit in a drill to spin the alternator and turned down the slip rings with various grades of file and glass paper. (Incidentally Ametlib, there was no voltage produced via residual magnetism when running it on my electric drill) I fitted the brush pack refitted everything and all worked fine.
I refitted the alternator and connected it, but before I put everything else back, switched on the ignition and ran it up with the drill - the light went out (and the drill started wheezing with the strain)

I took a couple of pics, so I'll try and do a 'how to change alternator brushes' at some point

The battery voltage was low - about 11 volts when I first started the car due to the buggering about without the alternator working. The voltmeter took a few seconds to come up to about 13.5volts, where it sat for quite a while before coming up to 14.some volts once the battery had recovered. A 120A alternator will not put out 120A at 14V, so I think if the battery is low, the voltage is slow to come up due to the current drawn. (Bloody Ohms feller again!) My giant battery may make this worse in the cold as it will take more current at a faster rate than a standard size battery.

[ametlib]

Excellent work!
About the instruments in our cars, I'm not convinced they are there to perform exact measurements in real time, more to reassure the driver, I think.
Take for instance the temp gauge, it will show 90 to anything between 40 degrees and engine core meltdown !!;);)
Sorry, too much coffey !;) But for the record, anything berween 78 and 105 degrees. Not convinced the voltage gauge is much better, so the delay up to 13,5 volt, hmm, not so sure my multimeter would have showed that.
Remember that Mr. Ohm , Mr. Volt and Mr. Ampere are friends with everyone who knows the relationship between them:beerchug: