Hi folks,

After replacing the battery a few times now - every 12 months - I checked the volts on my alternator output and am outputting 15.9 to 16.02 volts from the alternator.. Well the voltmeter is reading that across the battery terminals..

I suspect this is what is cooking the battery over time and hence I need to keep replacing it..

Couple of simple questions really.. What are the expected alternator voltage ranges on an x-type? Is the obvious cause a faulty regulator on the alternator or could this be a wiring loom issue? How can I determine the true root cause?

Any thoughts or suggestions would be much appreciated...

Am happy to change the alternator but they're not cheap and can be a pain to remove/replace..

Thx
Axelf

 

I'm no expert but that's pretty high. Probably too high even for cold charge. A 12v system should not be charging at 16v.

Measure at the alt positive post to verify. I'd go out on a limb here and if it is indeed charging that high constantly (hot/cold) the internal regular is bad/ PCM? Issues. Higher then normal charge is expected when "topping off" the battery but 15.9/16v constantly could cause bigger issues then fried batteries in a 12v system.

In my Jeep with 3 batteries and a mechman 270amp alt, it would never charge over 15. Just food for thought.

 

Thx for the feedback, I suspected as much.

Having said that, I followed busters advice and put the car into test mode (holding the trip button whilst starting the car) and monitored the alternator charge level this morning...

Started off high.. Around 15.2, then after a few minutes it dropped to 14 and after 5 mins was ticking along nicely at 13.2...

According to some other posts this is as expected on the x-type...

I will do a check at the battery with my meter and compare iit to what the car in test mode is telling me, hopefully everything is ok.

One thing I have noted in the posts is that jag's are brutal on batteries so having upped the battery from a 62/540 to an 80ah/760amp one I am hoping it will be better able to handle the demands ... The car only clicks on the starter if the Amps drop below about 250-280 and my old battery was only just charging to 300...

Axelf.

 

Jaguar spec for X Type batteries is

Petrol - 80Ah 680A, Diesel 80Ah 640A

So you were struggling with a 62/540 and even an 80/760 is not quite there!!

15.3 to 13.6v is the correct range for a petrol but it can vary depending on conditions

 

JTIS explains the higher voltage.

I think you need to use an old-fashioned lead acid battery in case you're not doing.

 

Well that just figures! I went to my local motor factors supplier and they entered my car reg in their computer and came up with the 62/540.. Goes to show, never trust a computer or is that a motor parts company!


The 80/760 is just above the 80/680 that you have quoted for Petrol so it will be interesting to see how this one does over the next year... Will let you know..

 

I have got a YUASA Silver HSB096 with a 5 year guarantee - supposed to last 50k engine starts against a normal 20k engine starts...


I have put a note in my car folder with the receipt so that I will be able to try and claim (note the word 'try') if it fails before then. I would say I'll let you know... but seriously!

 

In case that's the wrong technology it'll be the wrong battery and may not last.

 

Axelf, I want you to try something for me. I want you to pull the cigarette lighter out of the center console and have it so the terminals are reachable with your multimeter. Start your car and put it into the diagnostic mode (like you did before) monitoring the battery voltage. With the car running, I want you to turn on your headlights, both seat heaters and the rear defroster along with the dash fan on the fastest speed. I want you to note the voltage the instrument cluster is reading and write it down on a sheet of paper. Now, using the multimeter, measure the voltage at the cigarette lighter. Write that down (do an idiot check and make sure the instrument cluster has not changed by more than 0.1 VDC, if it has, redo the cigarette lighter voltage check). Next, measure the voltage across the battery (again, check the instrument cluster indication against what you originally got) and write that value down.

You should expect to see all 3 of these voltages within 0.5 VDC of each other. If the battery voltage is higher than the other 2, then your power wire between the interior of the cab and the engine bay fuse box has a high resistance connection and you will most likely need to get that replaced.

If you find that the instrument cluster is reading much lower than the other 2 voltages, then you most likely have a problem with the ECM and that is what is leading to the too high of voltage.

If you have more questions, let me know. If you want to learn about batteries, let me know too. I work around batteries for a living. The ones I play with can power a small town (literally).

 

Thx Thermo for the detailed instructions on this, I am going away for a few days.. Will let u know the results when I get back....

 

You could be right, but as I already purchased the battery and it has a 5 year guarantee I will not worry too much. TBH, if I have a wiring/alternator problem then that is really my goal to get fixed.

 

Of course. So far the volts sound OK but no harm doing more checks.

 

Hi Thermo,

Did the tests, voltage from the dash.. 14.6, voltage from the cigarette lighter 15.6, voltage at the battery 15.7... So basically the car is stating 1 volt less output than my multimeter...

Will try and get another meter and try that... Perhaps my meter is on the fritz...

Axel

 

Axelf, if the dash is reading a lower voltage than the 2 meter readings, this would tell me that you have an ECM issue. In short, the ECM is getting 1 voltage to come into it, but it is not measuring it correctly and therefore thinks the car is running at a lower voltage than what it actually is. Therefore the computer attempts to raise to voltage to make the ECM voltage what it wants. It doesn't go higher than the 15.7 VDC since the field is maxed out and cannot generate any more field and therefore limits the voltage from rising any higher.

So, in short, sounding like you have a bad ECM that is no longer able to control the alternator. Before we just jump on a bad ECM, I want to try 2 things first. The first would be to access the fuse box under the dash and remove fuse F82. This is going to take out your TCM also, but this will also kill the main power to the alternator too. Now, start your car and put the instrument cluster into diagnostic mode. Does the instrument cluster still show a voltage of over 13.0 VDC? If no, then this is pretty much confirming a bad ECM. If yes, turn the car off and access the alternator. If you look, you will find 2 groups of wires. There will be a large, single wire and then there will be a plug with 4 wires on it. Disconnect the plug. Now, attempt to start up the motor again (putting the instrument cluster into the diagnostic mode). Does the instrument cluster indicate over 13.0 VDC? If no, points back to a bad ECM (granted, give the plug a quick look over to make sure things are not awry inside the plug). If the cluster is indicating over 13.0 VDC, then you have a problem internal to the alternator. You will need to replace the alternator.

 

I'd avoid that for now.

Instead, just measure with engine off: battery & what does dash tell you? Will probably be about the same 1V difference.

If you go for a drive of say 20 mins and without turning engine off do you find the 15.x has dropped to say 13.x or 14.x? It normally does, as the charging profile only wants 15.x for a while.

If all that's right then you don't have any fault.

 

Measured with the car running at 13.2 and meter showing 14.1
turned off and waited a while (ignition on but car not running)
car read 12.3 and meter read 13.1 at the battery and the cigarette lighter.


So as you suggested there is probably not a problem with the car and this is most likely all down to the motor factors shop selling me an under spec battery last year.


Now I have a proper spec battery in place this should not happen again.


Thanks JagV8 and everyone for your help and advice it has been much appreciated. Thanks also to Buster for the tips on getting the car into test mode, that helped greatly in this.


Axelf