2005 Type X 3.0
Battery light is on most of the time. Using engineering mode (if that is the correct term) the battery voltage varies between 12.3 and 12.9, mostly around 12.5-6. Battery at rest reads 12.72.
A lead acid battery full charge at 80 degrees is 12.650. The same spec for an AGM is 12.8. The question becomes does the charging system think there is a lead acid battery and gets confused with the higher full charge voltage of 12.8?
In any event it seems I should be fine with an AGM battery at about 85% charge and only have the anoyance of the alternator light?
Thoughts or comments?

 

I don't know for sure but I doubt the 12.8 AGM battery is causing the alternator/battery charging light. These cars have a 2 stage charging system. When you first start the engine you should see something like 15 volts across the battery. After 1 or 2 minutes of the engine running that drops down to about 13.4. If you are only seeing 12.5 with the engine running you definitely have a charging system problem.

 

I was afraid of that, thanks

 

You probably saw this thread, looks like the 2 of you are having similar issues.
https://www.jaguarforums.com/forum/x...y-what-282212/

Get at the alternator connector pins 2 and 3 as mentioned over there. Also check codes if the CEL is on, there are alternator codes that could help.

I had a charging system problem which turned out to be the wire providing battery voltage to the alternator had high resistance so the alt was getting maybe a volt less than battery voltage. The fix was splicing in $1 worth of wire so the least expensive fix ever. Good luck.

 

See if your battery & alternator cables are getting uncomfortably hot when it’s been running a bit. They fail/corrode internally (while looking pristine from the outside) which leads to more resistance/heat.

 

I would like to get a meter or a scope on the input pins to the alternator but I can't find a way to get to them. I just learned about using test pins into the rear of the connector and have some pins on the way. Even with them I don't see a way to get a hand in there to insert the pins.
The battery cables look new to me and I scuffed the grounds under the battery box which were very clean to start with.
The + cable measured about 150 degrees and the negative measured 127 or so.
I checked the resistance between the positive battery terminal and the postive post on the alternator when everything was hot from running and it measures 0 ohms.
Part of a paper label was falling off the alternator which I retrieved and it appears the alternator is a reman of some sort.
That's the current situation. Thanks for any help.

Has anyone tried replacing the alternator from the top? I have a write up that says you can remove the fan module, somewhat tricky to get it out, and that gives enougs room to access the alternator and remove it. I really would like to avoid coming up from the bottom and having to remove the AC compressor and open the AC system to get to the alternator should I decide to repace it.

 

What was the electrical load when you measured battery cable temperature? If you look through the forum here the recommended test for battery cables is to turn on lights, seat heaters, rear defrost, etc to get a lot of current and run it like that for at least 5 minutes. If you have a positive battery cable that is 150 deg F from self heating you have a bad battery cable. It sounds like you know electricity so you probably know power dissipated in a wire is current^2 x resistance. 50 Amps (guess) and resistance of a 1 meter 2 AWG cable (guess) from a chart is 0.0005 ohms gives about a Watt of heat. A Watt is not going to heat up that cable.

Testing the resistance of the cable isn't helpful. I'm repeating what Thermo and others have said here but if you measure resistance of a very thin wire that is 3 feet long you will measure 0 Ohms but if you try to run 50 Amps through it that wire will melt. The failure mode of these battery cables seems to be internal corrosion which limits the area for current to flow = area of high resistance = heat.

 

Good point.

 

I hope the bad battery cable is THE problem with your charging system and not in addition to a problem with the charging system. So many bad battery cables are showing up here on this forum lately.

I was able to find an OEM Jag replacement cable on eBay ~2 years ago for short money. Hopefully you can find something reasonably priced. JagBits, Terry's Jag, SNG Barrat,...shop around, the prices fluctuate.

 

If I have a bad cable I will probably make something. I see no sense in spending the sort of money Jaguar wants for a fancy cable clamp that tends to fail fairly often.

Copper is copper.

 

Just saw your other post quoting $850 and I totally agree. Standard battery terminal connects to 2 fat cables, one to the alternator and one to the underhood fuse box. If you don't have the tools maybe go to a hot-rod shop or a place that rebuilds alternators and have one custom made. That will be less than the Jag parts cost.

The only slightly tricky thing with doing it yourself, if I recall correctly, is the underhood fuse box has to come out because you need to remove the old and bolt the new battery cable underneath it. It isn't hard, just takes some finesse because there are connectors under the fuse box you need to press release clips on while looking at them with a mirror and a flashlight.

I'll post my cable source on your other thread.

 

Made some measurments:
104 degrees ambient current readings from clampon DC meter
Line from alternator to battery 65 amps voltage drop 0.120 R= .0018 W= 7.8
Line from battery to fuse panel varies with load from 20 - 105A.
At 20A battery voltage = 13.4 or so.
At 70A battery voltage =12.9 or so.
Max output from alternator 60=+/- A regardless of load on battery to fuse box.
I would really like to get a probe on the 4 pin alternator connector but haven't figured out just how to do that just yet.

Comments? Suggestions?

 

Also no codes.

 

I am encouraged by your 13.4 volts when the load on the battery is small and 12.9 volts which is still enough to charge the battery and not get a charging system light when the load on the battery is high. That seems normal.

Q: Does your charging system light ever come on when the engine is cold? Like within a minute or 2 after starting the engine? Or is it only after things heat up? The resistance of copper wires goes up with temperature so if you are fine for a few minutes but not after that it further implicates the hot battery cable. On the other hand if you get the charging system light on a cold start that probably indicates something not related to the battery cable is going on.

My recollection of the 4 pin connector at the alternator is pin 1 is a digital or maybe analog PWM signal to the alternator indicating how much current to produce. Hard to measure and harder to interpret unless you are able to measure the signal in milliseconds.

Pin 2 should be battery voltage to the alternator coils. If pin 2 is less than battery voltage (as was the case with my car) there is a problem between the fuse box and the alternator.

Pin 3 is the voltage of the field windings of the alternator. It is a DC signal that when working is proportional to the input signal at pin 1. Which is why measuring pin 3 and getting a varying DC voltage indicates the signal at pin 1 is working fine.

Pin 4 is just the wire to the charging system light on the dash board. If your charging system warning light is coming on this connection is probably fine.

That is why I would concentrate on pins 2 and 3. If pin 1 is working than pin 3 is varying so pin 1 is likely fine. Pin 4 is probably fine because your charging system warning light is on.

 

The charging light is often not on when I start but comes on anywhere from a few seconds till often the first little bump I hit. It will rarely go off while driving which is all done with the AC on so something like 70 A load.
The car was hot and had been idling for better part of 10 minutes when I took the measurements the + battery lead was reading something like 15x degrees or so. The negative lead runs cooler by 20 or so degrees.
The ambient is often 100+ with upper range of 115 or so. It does the same when it is cooler. About 75 is as cool as it gets at this time of year here in Tucson.
I have seen 13.9 on the dash with the charge light on. The charge light was on at 20 amp load.

Seems like it should but I am not sure my rather old Scan Tool will pick up alternator codes. It has limited access to sensors. I probably should call Scan Tool and ask.

The alternator is some sort of rebuilt as I was able to retrieve part of a tag that was peeling away.
Perhaps I should carge the battery fully and see if the 50-60 amp charge current goes down at the 20 amp load, showing some control of the charge rate.

I should try driving with 20A load and see what happens. Perhaps I will try that tonight, I doubt the lights will add much and most if the increase comes from the AC, probably the fans.

 

More measurements Ambient 107 freshly charged battery
Start car with minmum load and no charge light. Battery 14.5 Idle 8 minutes, no change. load current 20A charge current 45A
Drive for ~20 minutes still no charge light. battery voltage 12.8, load current 20A charge current 20A
Add load and charge current goes up as load added. At load current 74A (AC on) the charge current is 65A. Still no charge light because I suspect the system has to work at a deficit until the battery voltage drops before the charge light kicks in.

My conclusion: Alternator and control circuits are working as they should with limited current. Alternator is only capable of 65 A probably due to open diode.

Solution: find open diode and replace or replace alternator.

Comments?

 

Finished the alternator install today and all seems well.
I used a rebuilt Nipon Denso by AC Delco from Parts Geeks about $250. It came with a note that said it was set up to charge at two rates, low and high. I haven't had a chance to check the charging current but I suspect it is fine as I have driven it about 50 miles with no problems.
I replaced it by trying to follow a U tube that removed it from the top but could not get to the alternator because the thermostat housing would not clear the fans to remove the hose between the radiator and engine. I wound up removing the radiator and it was pretty smooth sailing. The lower bolt on the alternator comes out from the right side near the serpintine belt. I bought a belt tension tool from Harbor Freight but the 3/8 square was not clocked to allow it to insert into the tension arm. I cut a V out ot the bar and bent it to about 30 degrees and welded it up. Worked great after the mod.

Removing the front bumper made things much easier however I was unable to get the tabs in the bumper to enter the slots so it sticks out a bit. Seems like that will be ok.
It was difficult to get the lower radiator hose on all the way but it finally seated. I used a pry bar to apply pressure to push it on.
I replaced the radiator by myself by looping ropes around each end and inching up a little bit at a time. Tedious but it worked. Hope that helps someone with the same problem or similar.

 

Well it tuns out the new alternator acts just like the old alternator with a max charge current of 68 or so amps.
I finally removed the AGM battery and replaced it with a flooded lead acid and wonder of wonders it all seems to work! The alternaror now puts out more amps than is being pulled from the battery at the initial high charge rate then drops to a lower rate where it pretty well matches the output. I loaded up the system to about 85 amps and for the first time the alternator kept pace matching the load. I have driven about 100 or so miles and no problem. First time I have been able to do this without the alternator light.

Apparently the control circuit gets confused by the different charteristics of the AGM battery and will not respond properly. I believe the problem was due to the AGM battery all along and I did not need to change the alternator. I feel that this answers my initial question as to an AGM battery causing problems. It certainly did on this Jaguar.

 

Thanks for following up, might help a few people in the future.

 

One of the things I read about AGM batteries is if it receives a charge above 15, it destroys the battery. They also require an AGM specific charger that is completely different than the "traditional" type charger we probably all use/own. Well, our 2 stage alternators do charge above that. That probably has an effect on the electrical system in our X's (?). Changing back to a "traditional" battery seems to have corrected your problems, so I guess let sleeping dogs lie.