Possible dying alternator!
Hi folks,
I'm having issues with starting and charging.
Overnight, the battery dies.
When sitting, battery voltage keeps dropping. When running, the alternator puts out around 13.63v at idle and 13.68 at 2000rpm.
5 minutes after running battery at 11.7v resting.
​​​​​​​Any ideas please?

 

Guessing at best, no idea what you playing with.

Alternator is #1 on my list, depending on Year Model of the car, and the make of said alternator, such as Lucas, Motorola, Bosch.

A very old battery, that is sulphated inside, may also be causing alternator issues, but not necessarily a faulty alternator.

Bad earths will reek havoc on charging ability.

Once you clarify the car, and the alternator brand, more specific answers will arrive.

 

84 sovereign 4.2 sorry,
Guessing it's a Bosch, here's a pic of the back, but haven't removed yet.
The 2 thick h
brown wires. 1 goes to the battery positive and the other goes to the headlight fuses and high beam relay. The thin one, brown black stripe seems to go under the air filter somewhere.

 

make sure something is not staying ON, like the boot light, or the interior lights. If the radio has memory presets, there will always be a little comsumption.

The best test is to replace the battery temporarily with a known battery.

 

Not sure why you think the alternator is a problem if youre getting 13.6V-ish. Sounds more like the battery has reached its use by date. Have you changed batteries already and that what leading you to the alternator?

You could have some parasitic loss happening overnight , but the battery seems more likely.

What voltage you see at rest can be affected by whatever static current is , and what the internal resistance of the battery is. If you take the earth lead off, you will get a real reading of battery voltage.

 

Thanks guys,
I've looked at all the lights and even set the camera to video and closed the boot.
My reason for thinking alternator is I'm more used to 14.2 or so, but this is my first jag and some things are just different.
The battery is not quite 2 years old, but I'm getting a new one anyway.
So if 13.6 is fine, I'm happy.

 

I'd say 13.6 is fine. Not optimal, perhaps, but nothing to be concerned about in and of itself.

I'm wondering if the car has been subject to some wiring mods that might enter into the problem? An alternator output wire going to the headlight fuse box is something I've not heard of on a Series III. And there appears to a large ground/earth cable on the engine mount bracket....another oddity to my eyes on a 6-cylinder car.

But I also acknowledge that there might be different wiring schemes depending on what market the car was built for. I'm accustomed to USA build configurations, obviously

Cheers
DD

 

Yeah, me too!!


The big brown to battery + makes sense.


The others mystify me. Not hard to do, though!!!


Carl

 

I tried my logic on one of my own cars , a Toyota Hilux (tacoma in US speak). This is a well maintained daily driver.

It has a USB do hickey in the cigarette lighter outlet. It has dual USB outlets but more importantly has a display that cycles cabin temp, USB current drain, and battery voltage.

Battery voltage accessories off > 12.6V
Voltage at idle > 14V
Voltage not running but accessories on > 11.7V

Pretty much like your car, just a slight diff in Alt voltages but both still enough to keep the battery happy.