Ammeter - Not charging?

[JD-JAG66]

I have managed to solve my transmission issues and so could drive it for the first time on the road (just a couple of hundred meters, since not yet registered)
Got back into the garage and noticed that the ammeter was on "C"



Turned the engine off.
=> I run a 4.2 engine (fitted with an Emerald injection system) out of an XJ6 which also provided the alternator.
Turned the key onto the "on position" and this is what I got:



Immediately after the engine starts running the needle flips onto the "C".
No blown fuses.

So, any suggestions?
If I have a charging problem, how to best check this?

Cheers
Jan

[Series1 Stu]

You're ammeter is operating in the charge side of the gauge so you don't have a problem with a failure to charge but perhaps a problem with over-charging.

Perhaps start with a voltage check at the battery terminals. Anything over 14.5 volts indicates a problem with your voltage regulator. I would suggest that your alternator is working alright.

Regards

[JD-JAG66]

Cheers Peter.
Will follow your advice and check at the battery next time I run the car.
Rgds
Jan

[chrisfell]

I’ve had this before.

The ammeter tells me the alternator is charging and the battery is drained. Checking the voltage, it should be around. 14 volts. If it is 15 or higher, the regulator is suspect. If the volts are at 14 and ammeter stays pegged at C for more than a minute or two then the battery is suspect.

With luck all it is, is a drained battery and all will be well once the battery is charged. In my case the battery had a short. I had a spare, and the suspect battery was demoted to non car use. It still holds a decent charge some six years later, and is used to power my electric jack impact wrench.

[Heuer]

Happened to me on my 3.8 with dynamo. The sense wire connection was loose. Basically as you rev the engine the alternator/generator will increase its output to over 20 volts. The regulator (4TR on the 4.2, RB340 on the 3.8) detects this and limits the charge output to below 14.3 volts. Either your regulator is faulty - common with the 4TR - or you have the connections wrong somewhere and the sense circuit is broken.

[johnetype]

I have managed to solve my transmission issues and so could drive it for the first time on the road (just a couple of hundred meters, since not yet registered)

=> I run a 4.2 engine (fitted with an Emerald injection system) out of an XJ6 which also provided the alternator.

From the information you've given I'd say this is normal behaviour. The alternator from the XJ6 can charge at many more amps than needed to drive the ammeter you've got to the "C" position and given you've only run the car/engine for a few minutes it's likely that your battery just needs charging and that's exactly what the alternator is doing.

Either fully charge the battery with an external battery charger before you start the engine again or just run the engine for longer and the needle should come away from the "C" position eventually.

Longer term it really isn't advisable to use an ammeter when you've got an alternator, it's one reason why Jaguar changed to a voltmeter on the Series 2 and I'd suggest you do the same as otherwise you have large currents running in and out of the dashboard wiring loom which along with overloading the ammeter as you're clearly doing at the moment increases the electrical fire risk.

As others have suggested, also check the voltage across your battery isn't greater than 14.5 volts with the engine running.

[Series1 Stu]

Yes, of course. If you're running the old 30 Amp ammeter it will be overwhelmed by an alternator. I swapped the internals of mine for a 60 Amp gauge but kept the original case and dial so it looks perfectly standard.

Regards