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Voltage gauge accuracy

asterix_the_gaul

Well-known member
Joined
20 Dec 2008
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1,315
How accurate is the voltage gauge?
Took a trip today and since having alternator issues on another car was watching the gauge and it was only hovering over 12v, dependant on how much stuff I had running. not got a voltmeter in the car to check what im actually getting, but what does your voltage gauge read ?
 
Thanks guys, it started again fine last night when I went out for dinner, I was having anxiety issues after being stranded last weekend driving the heritage vehicle with duff electrics.
Have several voltmeters at home so will check when I get back, did my anxiety no good when I realised I had taken the jump leads out Of The frunk for the other car last week..
 
Mine reads around 11.5v when engine is not running (my battery is over 6 years old and only an S3) and up at 14v when running.

As a quick easy check, pull up against a wall in the dark, switch your engine off, put your headlights on. Start the car and see how much brighter they go with the engine running.
 
So took some readings as soon as I got back, the voltage gauge reads about half a volt lower than it actually is.
Measured with voltmeter, Hot, when I just got back after 2hrs on the motorway, at the battery, 12.5v engine off hood open. Just started 12.6v hot, 12.7 back in the engine bay off the jump terminal. That's not charging though at that voltage, but is it a clever system that senses when Batt needs charge?

Cold this morning it read 14v just after I started it up from the dash gauge which held for a minute or so before dropping to 13.5 ish. Later in the motorway it was reading about 12.5 on the dash, but dash reads about half a volt lower than what's seen at the battery.

Just seems a bit weird? Not run out of electricity ever but it's not a new battery by any means and it's usually sat on a trickle charger during the week
 
Obligatory photo, I hadn't actually broken down or sprung a coolant leak..
 

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Car hot / running , headlights on , main beam on .. fog lights on radio .. heated seats .. anything electric ..

voltmeter on the battery and not the gauge .. if below 13 volts then your alternator is on its way out .

Cold / hot and a faulty alternator will give different readings .

checks are always done via a separate volt meter .
 
So finally got resolution on this one, had the alternator changed and it now puts out a solid 14volts on the dash gauge all the time when the engine is running. It did eventually kill the battery as the alternator was not charging it when it started to give up. Having it on trickle charge kind of masked the problem for ages.
 

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