My wife's X type didn't start the other day. Not sure why but she called aaa and they jumped it. Started fine and the battery had a great charge but I ran it thru a cycle of the battery tender anyways. Only took about an hour til it was solid green or charged. So I took a volt reading at idle. It is putting out 15.2/3 or so at idle. goes up to 15.4 or 5 with increase in rpm. I see they have a dual regulator but if the battery is showing a 12.6-12.8 after some time to rest wouldn't the regulator be using the lower charging amount? I did add some soda to the neg cable as it was a bit powdery but still not sure why it didn't start for her the other day.

 

Trevor, the high voltage may be caused by a few things. First off, how long after starting the car did you get the 15ish VDC reading? The car will artificially raise the voltage for a period of time (based on how far the battery voltage drops during starting) to top off the battery from the power pulled during starting the car. But, even under abnormal conditions, after a minute or so, it should have lowered to 13.7VDC or so.

The other potential problem is there is a wire that senses the voltage going to the car and this gets fed back to the ECU. This is what the ECU uses to set the voltage output of the alternator. So, if you have a resistance in either this sensing wire or the battery wires, you can have an artificially high voltage since the ECU is seeing a lower voltage.

 

Probably let it run about a minute or so it might not have dropped yet if it is a timed thing, that would be too high of voltage though right for a long term? I'm not crazy on that am I? So the ECU sets voltage not a regulator?

 

I think it's like the S-Type and has the higher voltage for a while to condition the battery. Normal - and detailed in the free download workshop manual

 

Trevor, yes, you are correct. The ECU keeps the voltage high to recharge the battery for the power it lost starting the car. The rate of charge to a battery is relative to the voltage above the battery when it is sitting there with no outside connections to it (ie, the 12.6 VDC for example when the motor is off). So, by raising the voltage for a short period of time, the battery gets a boost of energy. For short periods of time, doing this to a battery is no problem. When you do it for long periods of time, that is when battery damage can happen.

The ECU is programmed to look at the voltage that the car is seeing for all the computers and attempts to keep it at a constant value even when loads are being added and subtracted from the electrical system. This helps to keep the computers from giving erroneous errors and also to prevent an under/over voltage condition, resulting in component failures. The voltage difference occurs because all wiring has a finite amount of resistance to it (may be very small, say 0.01 ohms over a 10 foot run), but when you start running say 100 amps through that same wire, it will result in a 1 VDC loss (using ohm's law, voltage = current x resistance or 100 amps x 0.01 ohms = 1 VDC). So, when you have lots of stuff turned on in the car, the voltage at a far point in the car will actually drop. This same effect can be seen to a degree in cars that have a large current draw from the radio and the headlights flash with the beat of the music (granted, most of this dimming is coming from the fact that the alternator is getting overloaded and its output is dropping off).

As for how long that the ECU keeps the voltage elevated, it isn't a fixed time. It has to do with multiple factors. So, you have to give it a little bit. I would say to try this: start the car and go for a short drive (5 minutes). When you get home, turn off all electrical stuff and keep the engine running. Measure the voltage across the battery. You should get 13.7 VDC. If it is up at 15ish VDC, get back into the car and turn on your headlights, rear defroster, seat warmers, and the dash fan (max speed). This should put about a 90-100 amp draw on the alternator. If the voltage is still up at 15 VDC, then your alternator/ECU is not properly controlling things. If the voltage drops to 13.7, then we more than likely have a few things going on (issue with the voltage sensing line and a cable with a higher than acceptable resistance).

 

Thanks Thermo, you were dead on. Took about 5 minutes then it dropped down to 13.4-13.6 at idle. That 15 worried me. Now lets see if the mystery need a jump comes back.

 

The workshop manual is pretty useless these days with windows 10. My old laptop died. Boy do I miss XP

 

I've got Windows 10 Professional and JTIS works faster than ever! I installed it on my laptop when I was on Windows 7 iaw this link
https://www.jaguarforums.com/forum/x...archive-66011/
When I upgraded to Windows 10 Professional I didn't need to do anything with JTIS.
That link also installed the whole issue onto the hard disc, so I don't even need the JTIS disc in the CD Drive
These days it seems to be worth going for the Professional versions of Windows just for the ability to cope with older software, eg my Quicken finance program 2002 edition still works fine on Windows 10 despite reports that it won't!

 

Here's a handy inexpensive tool I bought from Amazon. With it you can easily tell battery and alternator condition from driver's seat. Shows static battery charge before engine start, then alternator voltage afterwards.

 

Yeah I don't speak geek so that is like reading directions from China to me. Still haven't gotten TuneECU and Autoingenuity to workand that I think is a simple driver problem.

 

Or just buy a used laptop with XP for roughly free.