The voltmeter in factory form is relatively useful with the key in the run position and while cranking to get an idea of the battery's state of charge. It seems as if Jaguar in their infinite wisdom dampened the gauge's input to filter out potential above 13 volts. This makes it necessary to enter the boot to check the charging circuit.

Would it be possible to somehow defeat whatever filter that they have placed on the gauge? Has anyone done this? Yes, the readings will be on the lower side due to the wiring scheme, but one can always assume a correction factor.

On a related note, here is a nice chart for voltage as it relates to ambient temperature: Battery Voltage Temperature Correction | All About Lead Acid Batteries

 

They put green food dye in mint jelly because the majority of the people expect it to be green , I'm just saying .

Someone recently had a 2 volt difference between the alternator B + post and the the battery B + post due to 2 loose battery cable connections other then the 2 end terminals . So that test point is not valid .

The gauge was designed to be used by an operator and not an engineer .

 

When I developed RealGauge a few years ago, I decided to just address the coolant gauge and oil pressure gauge because their limitations could actually lead to missing clues that could lead to engine damage. The voltmeter was not great, but I felt it was less important.

Eventually I am going to run out of parts to make RealGauge, because one of its key components has been obsolete for several years now. I have a stockpile, but it is dwindling down. Maybe at that time I'll redesign RealGauge with different parts and add the voltmeter also.

(BTW, the gauges are stepper motor type driven by software in the Instrument Cluster. The dampening is done in software. RealGauge works by entirely replacing the Instrument Cluster drive with a separate little computer).

 

Posted in error.

 

YES - 'relatively' being the operative word. I long ago came to the conclusion Jaguar gauges are just there to look pretty. Needles come in two types. Either they lock rigidly at the wrong reading or sway gently back and forth across most of the dial.

Jaguar have such a deplorable record for anything but the clock giving a correct reading that they've dispensed with most gauges on later models.

I had an upgrade on my 2005 XK8



The only accurate measure - the dipstick - has even disappeared from the later 5.0 litre models to be replaced by a gauge accessed through the message centre. On past performance, what chance is there of this being remotely accurate!

Graham

 

Thank you. I have your RealGauge conversion with the oil pressure option and it is excellently engineered.

it does make sense that the Voltmeter is data driven given the extensive CAN bus design of the car. This limits my proposed simple solution, however i wonder if the ECU or Body Control module needs voltage data and has such parameter available for scanning. this would make it as elegant as what you did for the temperature gauge.

going even further, we could do something similar to what the Japanese tuners have done for years and have gauge cluster packs that pull the data from the ECU. these are often seen pillar mounted or modified and added binnacles. since we often wish to keep originality, such a thing could be mounted elsewhere such as the center armrest storage. our cars are not often raced, but it might be nice to know things like trans temp and even oil (a sensor would be needed) especially for long hill climbs.

 

Strangely the one dial there that gives accurate information - the clock - doesn't even seem to do so flawlessly either:
am I the only one whose clock makes a loud "whirr" every minute as its hand moves?

 

yep, pretty standard for an electro-mechanical clock, good old 1960's tech. it is funny that they were installing a network that was very advanced for the time and even now and they did not use a clock with a solid state quartz mechanism with stepper motors for the hands. two possible reasons are that they were more interested in navigation as the future and the three gauge setup was bid out to a supplier who only had to follow the designer's visuals and interface specs.

 

Actually I have been inside the clock mechanism and it is a stepper motor driven by a quartz reference. Still makes a fair bit of noise however and only 'steps' on minute boundaries.

 

interesting, i stand corrected. was trying to visualize whether the face says "quartz". well then it is simply a case of loose fitting plastic parts making a racket. kind of has a charm to it.

 

I have been using scan gauge for over 4 years. Plugs into OBD connector. Coolant Temperature, air temp coming into intake, alt voltage as well as fuel miles. Love it. Easy hook up along with computer code reader keeps me well informed. Rich

 

Scan Gauge

 

Having a sat nav (upgraded to a modern Garmin) and thus no OEM volt meter, I went for a really good digital meter wired directly to the battery terminals via a press-to-make switch and an in line fuse. Readout is to two decimal places and thus a valuable, engineer's tool. It's fitted as the photo shows, in a small custom panel in the little tray in front of the J Gate.
I checked its reading against that of a direct handheld meter to see if there was any noticeable voltage loss in the wiring, the switch, fuse and connectors, but the differences were insignificant.

 

thanks, i will look into it.

 

thank you, that is an elegant installation.