Battery Charging Gauge

[Roger Kern]

My battery charging gauge shows near maximum when the engine is running, this is a recent issue. Measured the volts at the battery when running on tickover and that registered 13.9 volts, that seemed OK.
Can the gauge be fixed? Should I attempt to open it up and have a look inside? Any thoughts?

[tinworm]

Check voltage at 3K revs if its north of about 14-15 you have a problem with your voltage regulator.

Barrie
ps at idle I would have thought it would be around battery open circuit voltage

[Roger Kern]

Thanks for the information. I will check the voltage at 3k revs. Do you know what the voltage regulator allows as a maximum? What would I need to do to prove it was a regulator problem?

I am thinking it may be a gauge problem as in the past on very long runs (we went to Turin last year) it has been getting pretty hot to touch, however it always showed "normal charge".

Thanks again

Roger

[tinworm]

Hello Roger, your battery charging gauge is a voltmeter and should not get unduly hot. High voltage output from the alternator will boil off the battery electrolyte if not rectified - and damage the battery plates.
A voltage regulator can fail at any time. It should ramp excitation up as engine speed increases and the effects of load on the system (wipers , lights) try to pull voltage down. So it is always correcting itself. When a V/reg fails it can do so at zero excitation - or full excitation.

regards Barrie

[malcolm]

I don't think the volt meters on our cars work that well. Well, mine doesn't. Under load, on tickover, it will get down to showing i've got about 11 volts in the battery n- battery dying. Check simultaneously at the battery with a decent meter and it's 12.8. Fine. At revs, the car meter w ill show about 12.5 volts when real voltage is 13.9. So i'd check the real voltage at the battery to see if it's the meter at fault.

[tinworm]

Hello Malcolm, yours just needs a spot of calibration.

Barrie

[Roger Kern]

Thanks for your responses, I can tell you what happened as follows:

13.3 volts on tickover about 650rpm
Revs increased to 3000 and the meter showed 14.2 volts, dead steady.
Tried the same with the headlights on:
12.8 volts on the same tickover
Revs increased to 3000 and the meter showed 14 volts

All this time the voltmeter gauge in the car stayed on 16 volts, didn't budge!

Has to be the gauge I think.

Cheers

Roger

[malcolm]

Good check Roger. definitely the guage then. Your actual voltage seems fine, both under load and running light. Figures suggest the alternator is fine too.

[tinworm]

Yes something wrong with your gauge Roger - did you know new identical ones are available from Caerbont (think thats what they are called) They are licenced to reproduce Smiths back catalogue.

Barrie

[Roger Kern]

Thanks for the comments, information and advice.

I have sent the gauge off to Speedy Cables in Swansea for repair.

Always nice to get a second opinion on theses things.

Cheers Malcolm and Barrie!

[Terry S Martin]

There is a resistor in the circuit, it services the oil pressure and the voltage.
It is on the left towards the front of the pull down dash panel.
If it is shorting then both will over read.
I was never sure why it was put in place by Jaguar. I found little about it in the manual, if you need voltage numbers I can get them. I don’t have a good enough instrument to give you ohms numbers.
Terry

[johnetype]

Terry, you have a non standard car or are mistaken.

There is an electro-mechanical voltage regulator supplying an averaged 10 volts to the water temperature gauge and the fuel level gauge. It is not connected to the oil pressure gauge or the voltmeter.

There is a resistor in the panel light circuit to give you the dim illumination in the panel gauges but it has nothing to do with the gauges' readings.