Bl**dy alternator again!

[Jocklandjohn]

I noticed my tacho had stopped working properly. It works in as much as the needle moves but was sitting on the 300rpm mark and would not respond to revving the engine and then after a while it would get moving and go up to the correct idle speed of 800rpm (accurate because I checked with a strobe). 

I switched the engine off once the tacho had started working correctly, and then back on again and it immediately reverted to the 300 mark once more, and then repeated the odd behaviour, going up to normal once it had idled for a bit. Consistent with this I noticed the alternator note had changed also, becoming more noisy when the tacho worked correctly.

I've just stripped the wiring and checked it all, continuity to the W terminal etc all ok, and replaced the crimp-on terminal just to be sure. Back together again and it was still doing the weird behaviour.

I've just noticed that when the tacho is acting weird the voltage output is only 13.4v or so. Once it has idled for a bit, tacho goes correctly up to 800rpm and the voltage goes up to 14.5V or thereabouts. Switch off and back on again and I'm back to 300rpm and 13.5V output.*

*Output is measured at the alternator as I piggybacked a wire on the main terminal so I could check it in real time with minimum fuss. It also gives more-or-less the same readings at the battery. 

All the earth straps were disconnected, scrubbed and vaselined last winter and they all look good.

Is this a failing alternator? (its a new one, belt is new a few weeks back, pulley tight so no slippage.)

 

[Jocklandjohn]

Just had another look, with ignition on, engine off, the alternator dash light is off. When I flick key to start it flashed momentarily and then stays off. Voltage reading when switched on initially is only 12.7V and as it idles this increases slowly to around 13.5 (and tacho shows 300rpm and won't move with increasing revs) then there's a sudden jump at around 13.7v up to 14.5v (and as this happens the tacho starts to show 800rpm). The voltage output then seems normal (14.4+) but fluctuates and sometimes drops out. Voltage regulator?

[Peaklander]

Can you direct the strobe onto a mark on the alternator pulley to verify that it really isn't slipping?

[western]

Double post merged where required. 

[Jocklandjohn]

Thanks Ralph.

2 hours ago, Peaklander said:

Can you direct the strobe onto a mark on the alternator pulley to verify that it really isn't slipping?

I did that. At startup it was 984rpm and once it had warmed up it was 1080 - during which time the tacho was static at 300 rpm even when I blipped the throttle. The pulley seems to run at a fairly constant rate (on idle).

I just had a run in the dark and it was all over the place. The tacho stayed at 300, then it started to work and seemed to keep pace with engine revs. But the lights were pretty dim and the IBS battery monitoring system I've got was showing that the  charging voltage was fluctuating considerably (green led's go up and down) and this was confirmed by a small led meter attached to the battery which was showing 12.3v, the up to 12.8v, into the low 13v range and then up to 13.8v.

By putting all the lights and heater fan off, the voltage display got into the low 14v range and the IBS monitor got out of the green range and into the yellow 14v charging range. Whilst this was going on the tacho was either staying put or stuck on 300. Then the EGT gauge went to EEEEE which is some kind of voltage error.

I'm kind of stumped!

[Peaklander]

I've just had a read around and here's a copy/paste. It makes some sense and suggests that your alt is working but shutting down because your battery is fully charged.

If it sounds plausible to you, do you have a partially charged battery to try?

P.S. I should say that I don't think an alternator has a multi-step regulator but I think that they are intelligent enough to control their output as the battery state changes.

 

 

 

[Jocklandjohn]

43 minutes ago, Peaklander said:

I've just had a read around and here's a copy/paste. It makes some sense and suggests that your alt is working but shutting down because your battery is fully charged.

If it sounds plausible to you, do you have a partially charged battery to try?

P.S. I should say that I don't think an alternator has a multi-step regulator but I think that they are intelligent enough to control their output as the battery state changes.

 

 

 

Well thanks for taking the time to find that! Thats a new one on me.

It does make a lot of sense, but this problem has only recently happened. This evening when I had all the lights on, heater fan going etc the tacho needle still didn't move. ANd the charging seems to rise slowly, then drop and start over again.

I've got two new batteries on order as my aux battery is not holding a charge. I have a spare ancient alternator and I might try it tomorrow and if it solves it - good, but if not it points to there being something in the wiring beyond the alternator. Thanks for the help thus far!

[Mo Murphy]

Indeed, substitution would help you narrow it down.

Mo

[Peaklander]

I wonder if it's a problem at the W wire's connection onto the winding which is affected by heat or vibration.

Trying another is a good plan as Mo says. 

25 minutes ago, Mo Murphy said:

Indeed, substitution would help you narrow it down.

Mo

 

[Jocklandjohn]

5 minutes ago, Peaklander said:

I wonder if it's a problem at the W wire's connection onto the winding which is affected by heat or vibration.

Trying another is a good plan as Mo says. 

 

 

Would problems with the w terminal have any effect on the operation overall though? (I'm no alternator expert!)

The behaviour is intself odd though - the cyclic nature seems to suggest something recurring. If the tacho starts working and responding to revs and I switch off, it reverts to being 'jammed' on 300 again. And does so every time.

I did think about heat but it cant possibly cool down that fast simply by switching off and then on again I'd think.

 

[Peaklander]

No it wouldn't affect the output as after all, it's just picking up a very low current signal from before the regulator. Maybe that's my red herring. Sorry. 

Howver what if you have a bad connection down the output side to the loads ( battery itself or on into the truck)? That would really confuse the regulator and the tacho would reflect this. 

[Jocklandjohn]

11 minutes ago, Peaklander said:

No it wouldn't affect the output as after all, it's just picking up a very low current signal from before the regulator. Maybe that's my red herring. Sorry. 

Howver what if you have a bad connection down the output side to the loads ( battery itself or on into the truck)? That would really confuse the regulator and the tacho would reflect this. 

I had a similar occurrence to this last year which is why I fitted the new alternator, not quite the same but just unusual charging behaviour and erratic voltage - but fitting the new alternator remedied it - or so I thought. I wonder if simply fitting new batteries will be the solution. I'll go over it all tomorrow and see if anything behind the alternator is amiss - its an awkward bugger to get at! Thanks again!

[Mo Murphy]

May just be a duff regulator on the alternator. As we said earlier you need to try a replacement to narrow down the problems location. 

Mo

[Jocklandjohn]

Update.

Went out this morning, and before messing about and pulling the new alternator off I fired it up, tacho working on the nail 800rpm, 14.5V coming off the alternator at the rear and at both of the batteries, all appropriate LED indicators on various things lighting up correctly. Applied full load - all lights, spots, stereo etc and even at idle with all that stuff going it was still chucking out 14.2V. 

I would say thats a healthy alternator.

Then I went underneath and pulled off the engine to chassis earth, scrubbed and vaselined. Then the two from the batteries to the engine as well. All were fine - I did them last year too. 

So if I'm ruling out the alternator (unless this is some weird intermittent alternator fault and it comes back again) where is the next link in the chain I might need to look at?

 

 

[Peaklander]

Hmm that's frustrating to say the least and I don't think I can advise but here's where you are I think. Note this is me thinking aloud.

Your alternator is charging your batteries because it all appears healthy on the dials and they aren't losing charge over time (what's going in > what's coming out). The voltages appear correct most of the time remembering that a fully charged battery will have 12.8v when not under load and no charging and the alternator should be delivering around 14v when it is running.

Your tacho is picking up a signal from one of the stator windings which would change in frequency as speed alters as well as amplitude (I think). This is in the circuit before the regulator pack (diodes to convert to DC) and it's on the fixed side so not related to slip rings or anything.

However the tacho shows some lower frequencies than you are expecting to see (you know that sometimes the engine revs are greater than what the tacho displays).

The alternator might be intelligent enough to reduce the output when the batteries are fully charged to the extent that the tacho gets a naff input (I don't know if this is really true but I was told once that it does happen although I thought that the regulator is simply a diode pack to do the rectification and not much more. Taking this further, if the alternator thinks that the batteries are not charged, maybe it would vary its output. This could be down to a bad connection on the +12v supply side not necessarily only on the 0v side

You've checked and there's no belt slippage which is unfortunate as that would presumably explain everything.

 

You said this...

On 25/10/2016 at 2:48 PM, Jocklandjohn said:

Just had another look, with ignition on, engine off, the alternator dash light is off. When I flick key to start it flashed momentarily and then stays off. 

It should be on when the alternator isn't spinning and IGN is on, as the excitation for the alternator is provided by the +12v feed that comes from the other side of that dash charge lamp. It's supposed to be on until the alternator provides enough volts to match this, at which point the current flow is negligible and it stops illuminating. As far as I know, this voltage passes straight to the stator but would still be connected to the regulator. Maybe a duff / faulty regulator could affect it and it is a bit weird that it isn't on at the start. Something is working in that charge lamp "circuit" as the alternator is getting started and then generating its own field excitation once it is spinning.

Go back to plan A and swap the alternator!!

 

I've just read this back - it doesn't help at all, sorry but I will press submit only because reading it through might cause someone who properly knows to come in and help!!

[Jocklandjohn]

Thanks for thinking it through again!  

This:

"It should be on when the alternator isn't spinning and IGN is on, as the excitation for the alternator is provided by the +12v feed that comes from the other side of that dash charge lamp. It's supposed to be on until the alternator provides enough volts to match this, at which point the current flow is negligible and it stops illuminating."

So basically simply turning the ignition on, but not starting, should have the lamp lit. Then when the key is turned to fire the engine up, the lamp should go out? 

Ok that's pointing to something in the exciter wire circuit. I'll have a look at that behind the dash. I had a bulkhead fitted some years back by a "well known restorer of Land Rovers" and I've spent ages sorting out some of their wiring disasters - my Eberspacher heater being one example - they cut the loom and then patched it with odd bits of wire and caused massive voltage drop so then tried to fix it by tapping into the heater circuit, the lights circuit etc and caused a nightmare which I only recently was able to sort out. So goodness knows whats going on in the starting/charging circuit!

[Jocklandjohn]

I saw this morning when trawling the archives:

 

Paul Woodward

• Old Hand
•  
• 
• Long Term Supporters
• 
•  2
• 292 posts
• Location:Swindon/Wiltshire

 

 

Take the warning light wire off of the alternator and connect it to earth. If the warning light is then lit you have an alternator problem.

If there's still no light then the issue is elsewhere.

At the warning light panel remove the bulb and check for a 12v ignition supply at the bulb holder, if ok check for continuity from the other side of the bulb holder through to the alternator.

If the diode is missing or failed then there will be no continuity between the warning panel and alternator, it will be in the dash loom somewhere.

The resistor is connected in parallel with the warning lamp, if the bulb blows it will still allow an exciting current to pass enabling the alternator to charge. Even if the resistor is missing the lamp should still light.

Hope that helps.

[Jocklandjohn]

So, as my alternator bulb does flash on when the ignition is turned far enough to start, that suggests that there is continuity between the bulb holder to the alternator, but that the circuit in the 12v supply TO the bulb holder is NOT engaging? Am I right in that conclusion? 

[Peaklander]

3 hours ago, Jocklandjohn said:

This:

"It should be on when the alternator isn't spinning and IGN is on, as the excitation for the alternator is provided by the +12v feed that comes from the other side of that dash charge lamp. It's supposed to be on until the alternator provides enough volts to match this, at which point the current flow is negligible and it stops illuminating."

So basically simply turning the ignition on, but not starting, should have the lamp lit. Then when the key is turned to fire the engine up, the lamp should go out? 

Yes - the warning lamp is on from when IGN is selected until the alternator is providing enough of its own output volts (so as soon as it is spinning really).

 

3 hours ago, Jocklandjohn said:

So, as my alternator bulb does flash on when the ignition is turned far enough to start, that suggests that there is continuity between the bulb holder to the alternator, but that the circuit in the 12v supply TO the bulb holder is NOT engaging? Am I right in that conclusion? 

The lamp has IGN controlled +12v on one side and the other side is connected through a diode, to the alternator regulator and down to 0v. The current this provides in the stator windings creates enough magnetic field within the alternator for the rotor to start to generate its own power (to the vehicle).

The diode is there to prevent a back feed of current from the alternator once it is spinning and providing its own power. I don't think it does anything else.

For the lamp to light even just momentarily I think there must be a satisfactory connection from the IGN +12v all the way to the regulator. Then for it it go out almost straightaway I can only think

either 1) that the regulator is faulty as it shouldn't allow the volts to rise on that side until the alternator output provides them. As it is also connected internally to +12v from the battery (part of the monitoring of the battery condition to control its own output) perhaps it is this voltage finding its way to this side of the lamp.

or 2) that excitation wire from the lamp, through the diode, to the regulator on the alternator, becomes disconnected or high resistance and there's no longer enough current to drop the volts across the lamp. Could this be happening sporadically as well as when the unit starts to spin?

 

Otherwise I'm b*&&ered if I know :-(

[Jocklandjohn]

Thanks for thsi! Well I'm straying into terra incognito now!

Although all this electro-weirdness is going on the starting is brisk and fires up first-time winter or summer. I think I'll take a poke around in the dahs next and see if anything looks awry. Will report back!

[Jocklandjohn]

Right  - some early morning web sleuthing has revealed some useful info. 

My vehicle started life as a 19j and now has a 200tdi. The original wiring, including (AFAIK) the engine loom is still in place. 

Seems there's a resistor in the circuit that is described in this post I found. and although the post is about a fuel solenoid problem, its still relevant. Good pic of the circuit too. The author states:

"The highlighted wiring shows power being delivered through the ignition switch to the fuel stop solenoid and then onwards to the ignition warning light circuitry. The effective path from ignition switch to alternator sensing terminal is via the warning light bulb, which itself has a resistor wired in parallel. The resistor is to ensure that voltage still reaches the alternator in the event of a ignition warning bulb failure.

In a 19J engine, all would be well. Enter now a 200TDI conversion. The fault as it turns out is that when the ignition is turned off, a small amount of voltage ( Approximately +2.5V as it happens ) manages to backfeed through the warning lamp and head back to the fuel stop solenoid. It appears that depending upon the solenoid ( Age and condition no doubt ), +2.5V is enough to keep it energised and therefore prevent the fuel stop solenoid from cutting the engine when the ignition is turned off. The fact that the original FSS would close in this environment was one of the significant factors in delaying fault diagnosis, as well as a source of misinformation in Internet documentation on the issue.

Later Defenders which had a 200TDI engine fitted as standard enjoy a slightly modified wiring loom over the original 19J, most significant of which is a diode installed in between the ignition warning bulb and the alternator sensor terminal. This prevents the voltage backfeed and therefore cures the fuel stop solenoid issue that is seen on some retrofitted older vehicles."

I'm just wondering whether something like this is plaguing mine, given that it most likely has the original wiring setup? 

One other thing that struck me - I tracked down a weird noise in the alternator a few weeks ago - it was a delaminating belt that was not at all obvious until I removed it. Then the fun started - the belt matched nothing that the LR spares shop had listed for a 200tdi. It was slightly shorter than the normal 200tdi belt. However I bought and fitted the one that is listed as the correct part number even although its a tad longer as there is enough adjustment on the alternator to take it. And then I realised that its likely that the belt that was fitted is an old 19J belt, although I thought the 2.5/2.5td and 200tdi shared the same belt size (but I could be wrong).

But - if there is a belt length difference would the slightly longer belt affect the initial current output by spinning the alternator more slowly than the shorter belt, and affect the startup voltage given that the existing (old) wiring has been designed for a specific belt length and associated output? Or am I way off track with this line of thinking?

[Peaklander]

The reason for the diode as it says is to allow the stop solenoid to shut-off once the IGN has been switched off. As the alternator is still spinning it would still be providing output that kept the solenoid energised.

I don't think that this is linked to your problem - I suppose that if you don't have the diode because it's old wiring then you might have difficulty stopping the engine.

I should add that I only have a circuit diagram for a 300TDi and  the lamp wiring is different as the lamp has IGN +12v on it which then routes through to the alternator, with the diode in series and the resistor across the lamp. In your supplied image of the older wiring the lamp has 0v and the 'other end' has the IGN+12v running through the resistor first before splitting off to the alternator and the warning lamp.

[Mo Murphy]

At the risk of sounding repetative but I would really pull the alternator off and replace with a known good one. 

That way you'll be able to rule the alternator in our out of the equation. 

If I understood the last post correctly them the purpose of the diode is to prevent the backflow keeping the fuel stop solenoid open and so not turning the engine off.

Mo

[Peaklander]

Yes Mo, I read it as: the diode prevents backflow from the alternator that would keep the solenoid open and prevent the engine from stopping and I hope that's what I said too otherwise I'm needlessly confusing things (even more).

and yes swapping the alternator might well isolate the fault, as you suggested earlier.

[Jocklandjohn]

19 minutes ago, Mo Murphy said:

At the risk of sounding repetative but I would really pull the alternator off and replace with a known good one. 

That way you'll be able to rule the alternator in our out of the equation. 

If I understood the last post correctly them the purpose of the diode is to prevent the backflow keeping the fuel stop solenoid open and so not turning the engine off.

Mo

Thanks Mo. This is a new alternator. In fact the second new one!

I had a complete charge failure last winter whilst away working in the van. I got home and checked it out and it seemed the alternator was gone so ordered a new one. It arrived with a bashed box but seemed ok so fitted it and it worked for a few weeks then failed. I figured it had been damaged in transit so got it swapped. Fitted new one and it was all perfect until a months or so ago when I had a similar charge failure.

I swapped the second alternator for the old one which I'd kept and it all worked fine. I suspected a loose connection on the main feed wire + so pulled the old alternator off, replaced the terminal, cleaned and tightened everything and refitted the second new alternator. It has run ok for a month or so but just recently I noticed a variation in some of the charging led's on the IBS monitor and the tach started playing up. So this has suggested that the alternators are likely ok, but the problem lies somewhere in the wiring. 

When I was checking the connection to the back of the tacho a few days ago I was able to get the tacho needle to waver slightly by moving the wiring loom behind the instrument panel. I cleaned up a few connections and went on from there. What I didn't appreciate until peaklander has highlighted it, is the role of the alternator light and the fact that mine is off when it should be on, and that 12v feed is in pretty close proximity to the tacho wiring. So I'm wondering whether there is some dodgy connection there.