My interior and parking light has a flicker to it, and I measured a ripple of 1,5 - 2,0 Volts last year. As I live in Norway the car has been in winter storage since october.
Today I fitted a new original Denso alternator, but the problem still exist.
Charging voltage at idle are 14.3 V, and the connections at the alternator was clean and good.
The "funny" thing is that at the battery I measures only 70 - 80 mV ripple, but at the positive post in the engine compartment fuse box I measures 1500 - 1800 mV!
Any ideas? (No I do not need a new battery! :-) )
Normal?

 

Are you blowing any fuses ?

Have you tried giving those lights an extra ground to see if that impacts the voltage fluctuations ?

Z

 

Maybe a less than great ground or +12V connection somewhere between alternator & battery.

Should the alt be creating so much ripple? (I don't know.)

 

Nothing wrong with the car, just that the charging voltage fluctates enough as it can be seen with the naked eye that the interior (floor) light and parking light flicker.
It's not just the lights themselves, as I measure it at the main +12V on the fuse box

 

What I dont understand is why it so much better at the battery, but not at the fuse box.
The alternator are grounded through the bracket on the engine block, and I assume the ground between the engine and chassis are good because the starter works as it should?

 

The cheapest thing to try is to start adding ground to ground jumper wires at various points to see if you have a response.

I’m not saying I understand it either, but poor ground(s) have a wide variety of effects, one of which could be the anomaly you are observing.

Z

 

The alternator being a 3 phase device does produce a substantial ripple. It is much less at the battery as the battery acts like a big smoothing capacitor . Your charging voltage is spot on . On some models there was a large capacitor fitted near the altternator B to earth. are the bulbs flickering LED which are prone to flicker at end of life.
Checking the earths is a good idea but remember the only true earth is the battery negative so a long wire from that to what you want to earth is in order

 

In a word . . . no.

I sense that this flickering pre-dated the fitting of new alternator. I'm sure that you are aware that the voltage regulator is integral, but are you aware that the VR on later cars has a degree of smarts not deployed before 2003 (or thereabouts). The role of the VR serves to not only set the charging threshholds which are time and battery sense related, but also to "crowbar" the ripple you are seeing . . . by any standard, a 2V ripple in (say) 13V is around 16% so no wonder you see lights flickering!

First, re-check the alternator replacement, and check that VR.

Cheers and best wishes,

 

I was not aware that the alternator fitted to the XK8 was Computer controlled ie the ECU monitors charge voltage and adjusts alternator output .
There is no battery sense wire on a XK8 alternator and all the ones listed here in the UK show the same model alternator from 96 to 2005.

Any smarts are not incorporated into the voltage regulator but reside in the ECU.

Check the warning light for glow AT NIGHT even the smallest glow shows an alternator problem.
If you can get hold of an Oscilloscope and put it across the alternator output you should see an even ripple ..any cyclic anomalies in the trace are usually diode related.

 

With respect, are you not aware of the extra terminal on later alternators. If this is left unconnected or fitted to an earlier vehicle, some VR functions are inhibited. I bow to better knowledge of where the smarts reside, but I do know from personal workshop experience of the "smarts" in later alternator cars.

Previously, the VR is set to monitor and react to the battery charge state immediately at engine start. Later VRs do not. They set a high threshold (around 14V) for a set period irrespective of battery charge but designed to replace the depletion that started the engine . . . only then transforming to sense the battery state and setting the charge adjustment. This means that later cars will always start at the higher 14V setting and may only drop to around 13V after many kilometers of travel.

Certainly not seeking an argument, but trying to help the OP discover the cause of what appears a fault condition.
Flickering lights is not normal. Not on any of my Jaguars, nor any I have known.

Cheers and best wishes,

 

I will try to answer all at once. First of all thanks for all input from you that wants to help.
The ripple was there before I changed the alternator yes. Thats was the reason for doing so, the old alternator also had good charging voltage, but I thought maybe the ripple was from the alternator.
There is no smart about this alternator, charging voltage are regulated by the builtin regulator. Only two cables connected.
There are no LED bulbs on the car
There are no supression modul (capasitor) fitted to the alternator
As the electric diagram shows, there are one cable from the battery to the main fuses, and a single cable from one of the main fuses to the starter and alternator. Nothing else are connected to that cable.
From the other main fuse there are two cables, one to the fuse/relay box in the trunk, and one that goes to a stud connector inside the cabin where it splits to the remaining fuse/relay boxes inside the car and in the engine bay.
I will start to day and check if I have the same sort of ripple at every fusebox, try some extra ground from the battery here and there and see if there is something that can explain more of the problem.
I dont have any oscilliscope, but I think that must be the next step. Maybe the ripple has a frequency og pattern that can make some kind of sense.

 

Maybe a 1000uf capacitor from B+ pm the alternator will sort it out . electrolytic 25v or more rated

 

Smells to me like a problem with the main power distribution connection in engine bay. This coincidentally was the source of all my stalling issues a few months ago. I cleaned up all those contacts and replaced the LH fuse assembly and all that went away.

 

The three-wire alternator with the extra sensing didn't appear until the 4.2L.

1.8 - 2V is a lot of ripple. Curious:- how are you measuring it?

The 'suppression module' moved from its original place by the A/C receiver/dryer, but I think it sometimes gets left off after work has been done.

 

I am using a battery tester to measure ripple. No it is not a pro tool, so maybe the numbers are a bit off, but the ripple is there. A digital DC voltmeter are constantly changing and I do measure som AC.
What to the suppression module look like and exactly where should I look for it? I have not seen any cables or connectors nearby the alternator.
I have checked today and I have the same ripple on every fusebox in the car, including the main fuses. Odd (for me) that I measure ripple on the main fuse for the alternator/starter circuit at the battery positive cable, but no at the battery 30 cm away.

 

As posted, battery is rather like a big capacitor so the closer to it the less ripple makes sense I think, but there really should be little voltage drop along the hefty power cable & ground.

But if such a drop is expected then there ought to be something near the alt to deal with the ripple or the alt should not create it.

 

The only thing that by its nature generates a ripple is the alternator particularly with faulty diodes..Check the warning light at night for a glow.

 

Well, as the best solution for every problem solving and diagnostic work - just change everything at once! :-)
Today I removed battery, battery cables and main fuses from the car.
Hooked the battery to a battery charger
Cleaned everything (looked good but you never know)
AND connected a condensator aka suppression module. Info showed that the original condensator is 22000 uF. My son had one that was 10x that, but what to loose?
Reconnected everything, and hoped for the best.
New readings are 400uV ripple at the engine compartment fuse box. Last reading before todays work was 1800uV.
The result is that I no longer can see interior lights flicker.
Should I get hold of a 22000uF condensator instead or is bigger better?

 

If the original was 22000uf then anything above that is fine I would still be inclined to check the output with an oscilloscope if can get one in he future . 22000uf is a huge capacitor but no doubt required in vehicle development . Most cars would have 3 uf to supress radio interference'