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Old 8th January 2020, 21:14   #11
Atlan
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Have you checked for the AC voltage at batterry with car running as advised ?
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Old 8th January 2020, 21:27   #12
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Quote:
Originally Posted by Atlan View Post
Have you checked for the AC voltage at batterry with car running as advised ?
There won't be any AC voltage at the battery.

His multimeter gave him 14.6 volts DC.
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Old 8th January 2020, 21:30   #13
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Originally Posted by trikey View Post
I’d suspect a dead cell in the battery, the live feed from the alternator runs directly to the battery via a join on the starter motor so not much chance of anything going amiss in that area.


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The OP said his battery is holding at 12.8 volts when it's disconnected from the car.

A dead cell would show around 2 volts less than that.---
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Old 8th January 2020, 23:29   #14
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Originally Posted by pletevl View Post
Hi Mike,

No FBH on this car.

Can an alternator pump out 14.6 volts and NOT charge the battery ???

Pete.
Haven't heard of that happening - how accurate is your meter?
I worked on a Rover 400 once that had a similar issue but it was charging at around 12.7 volts so a fully charged battery would run down over 2 to 3 weeks of short runs.
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Old 9th January 2020, 14:55   #15
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Atlan, no, not yet checked for AC voltage, too cold and wet here to be outside.

Mike, I have 2 multi meters and a cigar lighter volt meter and they all show 14.6 volts engine running.

I am going to put the battery on this weekend and do some more tests, one that I want to do is turn the lights on before I start the engine and see if I see a difference in brightness as the alternator kicks in. I see it every day on my ZR and hear it too with the petrol pump that speeds up after a second or so.

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Old 9th January 2020, 22:01   #16
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Your alternator is good because the charging voltage is correct at 14.6 volts.
Your new battery is good with a resting voltage of 12.8 volts.
So if your battery is being charged and holding charge, that leaves an unknown discharge overnight.
Which generally means for a R75 the ECU plenum flooding, the satnav, FBH, interior lighting, (it just MIGHT be alternator diodes) or it could be the front wipers activating, flattening your battery overnight. That's been seen many times, when conditions are damp.
Put something on the windscreen (like paper) that will be wiped away if you suspect wipers are activating with ignition off.

And AC voltmeters have little to no use on a car.
https://the75andztclub.co.uk/forum/s...43&postcount=5

Last edited by MarkS; 9th January 2020 at 22:47..
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Old 10th January 2020, 10:45   #17
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The plenums are not blocked.
There is no FBH, no satnav.
There is a Naval1 stereo
Never heard of the wiper problem, what causes it ?

Pete.
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Old 10th January 2020, 23:51   #18
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https://the75andztclub.co.uk/forum/s...ighlight=Wiper

https://the75andztclub.co.uk/forum/s...ighlight=Wiper

https://the75andztclub.co.uk/forum/s...ighlight=Wiper

Et al

This has been seen many times.

There have been various reasons put forward, fault in the K-bus wiring, water in the ECU plenum paddle pool, or damp in the wiper park switch, etc

Various cures have been recommended, replacing the battery, disconnecting the battery for 20 minutes, draining the boot swimming pool, tapping the wiper motor, or cleaning dirt off the wiper park switch contacts.

My important point is that in all situations (and possibly many other incidents in our sometimes crazy cars ?) the problem may well be DAMP (after all, these incidents occur during damp winter periods, never during dry summer periods) and damp can DRY OUT, making the problem appear to go away temporarily or permanently, but as the person has :

1) changed the battery in the meantime,
2) reset the battery connection,
3) replaced the alternator regulator and diodes,
4) taken the car for an Italian tune-up,
5) offered prayers to the God of WD40,
6) prayed to their God of choice,
7) done a rain-dance around the car,
8) proffered some snake-oil from the god eBay,
9) offered goat blood sacrifices such that the gremlins go away,
10) etc.

They all appear to achieve the solution, whereas the reality is that the problem is good, old fashioned, dirt and damp (in the wiper connections et al), left out in the dirt and damp.

But as nobody may recognise that the damp has dried out, other solutions achieve mythical status

And as any decent engineer will tell you, goat blood sacrifices should be kept for those incidents which are unexplainable !!!.

Last edited by MarkS; 11th January 2020 at 08:24.. Reason: Rant
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Old 11th January 2020, 13:04   #19
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Quote:
Originally Posted by COLVERT View Post
There won't be any AC voltage at the battery.

His multimeter gave him 14.6 volts DC.
Agreed. That was on the DC setting. Change the setting to AC and try it.
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Old 11th January 2020, 18:19   #20
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I would query why you would expect to see an AC voltage across a heavy duty 12V DC battery.
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