High voltage
- Thread starter zcacogp
- Start date
red leader
New member
14.2v is the upper limit any higher and I'd be looking for a new alternator..
scam75
Well-known member
I get anything between 12 and 14 depending on how mine's is feeling! Typically it's at 14 when I fire it up, and will dip to 13.5 once the blowers or demister is on. Can sometimes settle about 12.5 after driving for a while then be back at 13.5 next time I look.
However, something has happened in your case to experience different readings than normal. The alternator could be on it's way out, keep an eye out for the battery over charging. I would get your multi-meter out first and see if your gauge agrees with it and take it from there. The voltmeter gauge is notoriously flaky and inaccurate in a lot of cases but I've found they usually read lower than the actual voltage rather than too high.
Hope this helps!
Stuart
However, something has happened in your case to experience different readings than normal. The alternator could be on it's way out, keep an eye out for the battery over charging. I would get your multi-meter out first and see if your gauge agrees with it and take it from there. The voltmeter gauge is notoriously flaky and inaccurate in a lot of cases but I've found they usually read lower than the actual voltage rather than too high.
Hope this helps!
Stuart
Thanks for the quick replies.
14.2v maximum? The red part of the voltmeter gauge is not 'till well over 15v (and it could be 16v). What happens at 14.2v?
The alternator was new in April 2008 and, at over £200, I'm reluctant to replace it again unless it really is necessary! What causes the voltage to go high? Presumably a failed component in the diode pack. Surely changing the component would be cheaper than changing the whole alternator?
What are the symptoms of a battery which is over-charging?
Good idea about getting the DVM out before getting too concerned about things .... thanks!
Oli.
14.2v maximum? The red part of the voltmeter gauge is not 'till well over 15v (and it could be 16v). What happens at 14.2v?
The alternator was new in April 2008 and, at over £200, I'm reluctant to replace it again unless it really is necessary! What causes the voltage to go high? Presumably a failed component in the diode pack. Surely changing the component would be cheaper than changing the whole alternator?
What are the symptoms of a battery which is over-charging?
Good idea about getting the DVM out before getting too concerned about things .... thanks!
Oli.
Super_Marv
New member
My CTEK battery conditioner has a winter 14.7v setting, so hopefully over 14.2v wont fry the battery!
ukmastiff
New member
Something doesn't seem to be getting mentioned here. Yes it is totally correct that the battery can correctly charge at just over 14 volts and no it shouldn't be much more than 14 but who says that the voltmeter on a 20 year old car is going to be accurate. This is often overlooked just as are oil pressure guages ?.
Oli, I would out a decent Voltmeter accross your battery with the engine running and get a true reading of what your battery is charging at before believing the accuracy of such an old precision instrument ( the Voltmeter), I.E it is just as likely to be the old Voltmeter at fault than the new Alternator surely.
Regards
Mas
Oli, I would out a decent Voltmeter accross your battery with the engine running and get a true reading of what your battery is charging at before believing the accuracy of such an old precision instrument ( the Voltmeter), I.E it is just as likely to be the old Voltmeter at fault than the new Alternator surely.
Regards
Mas
Also sealed unit type and conventionally vented types charge to either 14.4 or 14.7 v but I can't remember which is which.
sawood12
New member
Assuming your voltmeter is reading a rise in voltage correctly (maybe not the right value but the right trend) and you say your alternator is new, what about the voltage regulator? the usual sign on a voltage regulator on its way out is erratic behaviour - volt suddenly jumping up, lights going super-bright, fan blowing a gale, then everything returning to normal. However this may not be the only symptom. If your old voltage regulator was swapped from old alternator to new then i'd bet it is that.
As said before, confirm readings with a voltmeter across the terminals. It should be in the low 14v's with all the electrics off and over (if only just) 12v with all the electrics on (i.e. lights, fan, heated rear window).
As said before, confirm readings with a voltmeter across the terminals. It should be in the low 14v's with all the electrics off and over (if only just) 12v with all the electrics on (i.e. lights, fan, heated rear window).
Chaps,
Thanks for the various replies.
The scenario is a little more convoluted than just high voltage, as follows:
1. 10 days ago, while on a long journey, the tachometer was observed to 'bounce', down to zero and up to revs again, while cruising in 4th gear. Knowing that the tachometer is driven by the crank position sensor, this could be down to a sensor failure, but the engine ran smoothly at all times so I assumed it was an instrumentation issue.
2. 3 days ago, also on a long journey, the voltmeter was observed as reading very high (15v or so) when the ABS warning light (and main warning light) came on. This was at around 3000rpm in 5th, again while cruising with the car otherwise behaving totally normally. I decided not to stop (wanting to get to the destination), and after about 5 minutes the tachometer 'bounced' again (as above), the warning lights went out and the voltmeter reading returned to normal (smidge under 14v). Again, as always, the only thing to notice was the instrumentation - the car appeared to be running just as it should. I tested the ABS later on in the journey and it worked as it should. Watching the voltmeter on subsequent journeys it seems to start at around 14v and go up to possibly 14.5v or so at a maximum, but it wanders between a bit below 13v and over 14v depending upon what is turned on and so on.
I have (just) tested the voltmeter with a DVM on the battery terminals. 14v on the dash equates to around 14.4v on the DVM across the battery. So the voltmeter is under-reading. This was on idle just after cold start-up, with no electrical devices on (apart from the interior light). A bit of extrapolation suggests that the highest reliable reading I have had is therefore about 14.7 to 14.8v, with one peculiarly high reading which may be explained by a more general instrumentation fault.
This, to me, suggests that I shouldn't be worrying about the battery voltage but should be worrying about instrumentation. What sort of failure could explain the symptoms above? To re-cap, these are:
- Sudden drop of reading from the tachometer, but instant return to a correct reading, with no apparent drop in true engine revs
- Apparent ABS fault, with high indicated voltage, returning to normal with a sudden high tacho reading (as above)
All suggestions welcome - thanks!
Oli.
ETA: Scott, thanks for the comment about the regulator. It was replaced with the alternator (as I remember), so is of the same age.
Thanks for the various replies.
The scenario is a little more convoluted than just high voltage, as follows:
1. 10 days ago, while on a long journey, the tachometer was observed to 'bounce', down to zero and up to revs again, while cruising in 4th gear. Knowing that the tachometer is driven by the crank position sensor, this could be down to a sensor failure, but the engine ran smoothly at all times so I assumed it was an instrumentation issue.
2. 3 days ago, also on a long journey, the voltmeter was observed as reading very high (15v or so) when the ABS warning light (and main warning light) came on. This was at around 3000rpm in 5th, again while cruising with the car otherwise behaving totally normally. I decided not to stop (wanting to get to the destination), and after about 5 minutes the tachometer 'bounced' again (as above), the warning lights went out and the voltmeter reading returned to normal (smidge under 14v). Again, as always, the only thing to notice was the instrumentation - the car appeared to be running just as it should. I tested the ABS later on in the journey and it worked as it should. Watching the voltmeter on subsequent journeys it seems to start at around 14v and go up to possibly 14.5v or so at a maximum, but it wanders between a bit below 13v and over 14v depending upon what is turned on and so on.
I have (just) tested the voltmeter with a DVM on the battery terminals. 14v on the dash equates to around 14.4v on the DVM across the battery. So the voltmeter is under-reading. This was on idle just after cold start-up, with no electrical devices on (apart from the interior light). A bit of extrapolation suggests that the highest reliable reading I have had is therefore about 14.7 to 14.8v, with one peculiarly high reading which may be explained by a more general instrumentation fault.
This, to me, suggests that I shouldn't be worrying about the battery voltage but should be worrying about instrumentation. What sort of failure could explain the symptoms above? To re-cap, these are:
- Sudden drop of reading from the tachometer, but instant return to a correct reading, with no apparent drop in true engine revs
- Apparent ABS fault, with high indicated voltage, returning to normal with a sudden high tacho reading (as above)
All suggestions welcome - thanks!
Oli.
ETA: Scott, thanks for the comment about the regulator. It was replaced with the alternator (as I remember), so is of the same age.
peanut
Active member
could be Gremlins Oli .... but I'm inclined to believe that your car has been inhabited by none other than the Prince of Darkness .!
You should get your car exorcised without delay.[
]
ps ahem.... cough ....the regulator is a small voltage regulatory componant which works in conjunction with the diode bridge inside the Alternator to supply a smoothed regulated voltage output to the battery . http://www.thetoolboxshop.com/regulators-for-alternators-282-c.asp
You should get your car exorcised without delay.[
]ps ahem.... cough ....the regulator is a small voltage regulatory componant which works in conjunction with the diode bridge inside the Alternator to supply a smoothed regulated voltage output to the battery . http://www.thetoolboxshop.com/regulators-for-alternators-282-c.asp
tr7v8
New member
Been using my 944 in the snow as the Jag is as much use as a chocolate fireguard & noticed that my voltmeter has read higher than it has ever had. Around 14V. So it maybe the cold weather.
To check the alternator you need to load up the battery, with heated rear window, lights etc. & then with 2000RPM or more measure the battery volts.
To check the alternator you need to load up the battery, with heated rear window, lights etc. & then with 2000RPM or more measure the battery volts.
Nick,
Thanks, I think I'm with the gremlins explanation as well. It did a 120 mile trip back home yesterday, with radio and sidelights on all the way, and showed a very constant 13.9v (or so) on the dash cluster. Not a flicker of anything untoward. Given that all the oddities happened in the extreme cold, I wonder if it is seasonal.
Jim, thanks for your post. Looks like a very similar situation to me. Which is reassuring.
Oli.
Thanks, I think I'm with the gremlins explanation as well. It did a 120 mile trip back home yesterday, with radio and sidelights on all the way, and showed a very constant 13.9v (or so) on the dash cluster. Not a flicker of anything untoward. Given that all the oddities happened in the extreme cold, I wonder if it is seasonal.
Jim, thanks for your post. Looks like a very similar situation to me. Which is reassuring.
Oli.
George Elliott
New member
Oli, you said all suggestions welcome, so here are mine.
Change the battery on the car.
In my 20 years of maintaining my own cars, I have had 2 cases where I was baffled by strange electrical behaviour, - your rpm reading is the same type of thing. Both times, the battery replacement cured the problem.
If you want a bit of theory - perhaps the recent cold spell has caused movement within the cells? Has it seen a quick charge on the battery?
After that, I would consider the voltage regulator, you probably know it is attached to the alternator.
Both suggestions are relatively easy and inexpensive.
Only other thing may be - stick a turbo on it
Good luck
George
Change the battery on the car.
In my 20 years of maintaining my own cars, I have had 2 cases where I was baffled by strange electrical behaviour, - your rpm reading is the same type of thing. Both times, the battery replacement cured the problem.
If you want a bit of theory - perhaps the recent cold spell has caused movement within the cells? Has it seen a quick charge on the battery?
After that, I would consider the voltage regulator, you probably know it is attached to the alternator.
Both suggestions are relatively easy and inexpensive.
Only other thing may be - stick a turbo on it
Good luck
George
mr brightside
New member
Tacho driven from the crank position sensor!
Finally i might have a lead on why my DME relay fails to operate intermittently after the cars winter sleep! My tacho went through a stage of reading about 50% of what it should so perhaps the crank sensor's not delivering the correct signal to the DME when it won't start. I'm way off topic but hey, it's christmas...
Finally i might have a lead on why my DME relay fails to operate intermittently after the cars winter sleep! My tacho went through a stage of reading about 50% of what it should so perhaps the crank sensor's not delivering the correct signal to the DME when it won't start. I'm way off topic but hey, it's christmas...
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