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BX Charging fault - Bob Larder
I have a similar sort of problem to the AX, Alternator quit, tried 2 2nd hand units, both quit after 15 mins or so. They were charging, but were putting out around 16v before they blew. I`ve now put in a new unit, and a new battery, am still getting a 16v reading at the battery. Figures are-
ignition off 14v, idle 14.5, Rev it a bit and I`m back to 15,9-16v. I then cut the engine before I burn out this one!

I have tried setting the alt. up with a separate battery, isolated from the rest of the car, and get a reading of 14,7v at the battery. This would suggest that the problem lies < somewhere> in the car-
Ideas anyone?
Re: BX Charging fault - Michael
Bob, some thoughts:

1 - three different alternators each generating 16v at 2500rpm indicates that the alternator is not at fault

2 - the battery cannot generate 16v- so something else is.

3 - the voltage regulator unit is supposed to control the voltage delivered to the battery.

Question - where is the voltage regulator? As a guess, I would say it is separate to the alternator on your car.

I'm not familar with citroens, but i would try and locate the voltage regulator unit and test/replace it.
Re: BX Charging fault - David Woollard

It would be very unusual to find 14v on a "resting" battery. Are you absolutely sure the voltmeter is correct?

Re: BX Charging fault - Bob Larder
Just come off the charger, was told ( by a Citroen mechanic) that the problem was probably a faulty battery, so ensured that it was at least fully charged when I started. Still, worth checking the meter though, thanks.
Have now tried 3 batteries, so doubt that that is the problem.
I`d take the car to an autoelectrician, but it`s old and will be scrapped at the next test anyway, I just hate being beaten!
Re: BX Charging fault - Jeff Chambers
Stop worrying about the voltage, 16V on charge is not excessive. What you need to know is the alternator current output, it is excessive current that causes things to burn out.
You need a DC ammeter with a capacity of at least 150% of your alternator rated output. this is to be connected in series between the alternator and the battery. (Take care, the alternator lead is live with the battery connected).
If, engine running at around 2500rpm, you are getting much greater current than the alternator rating, you have got to find what is sinking the current - it has to be going somewhere! (Perhaps a short or intermittent short). However, I doubt if this is the case, you would have had other problems as well.
If the current is not excessive, then you have been unfortunate with your alternators.
Also, check the charging voltage at the battery with your meter (assuming it is a digital multimeter) set to read AC Volts. This gives you a quick check of the diode performance, you should get a low (ie less than 0.5 volt) reading. Any higher and you diodes are kaput.
Excess voltage problems? - David Woollard

Interesting comments. Have I been wrong for years in understanding that excess charging voltage will "boil" the acid from a battery and damage it?

Again I speak from observed experience, not scientific understanding, that an alternator will normally be charging at around 14.2 - 14.6 volts. This with a decent battery and at about 2500 rpm.

Re: BX Charging fault-Meter is wrong! - Mike Humpherson
If you are measuring a steady 14V across your battery when the ignition is off, your meter is reading incorrectly!

A 12V car battery cannot generate 14V on it's own, and with the engine off, there is no other power source which can drive the battery to 14V.

Mike Humpherson.
Re: BX Charging fault-Meter is wrong! - John Kenyon
Mike Humpherson wrote:
> If you are measuring a steady 14V across your battery when
> the ignition is off, your meter is reading incorrectly!
> A 12V car battery cannot generate 14V on it's own, and with
> the engine off, there is no other power source which can
> drive the battery to 14V.

Yes it can - but you don't actually have a usable 14v.
Under no load conditions, it wouldn't be unreasonable to expect 14v
at the terminals.

Same goes for other "fresh" or recently charged batteries.
Recent examples: 3xAA Duracells will give you 4.75v
(Used as an el-cheapo PC CMOS battery replacement!)
3v Lithium coin cell - 3.1v when replaced.

Both measured before being connected to their respective loads.

Re: BX Charging fault-Meter is wrong! - David Woollard

I never want to argue out a point to the last degree here, always ready to learn something new, but.....

I was speaking in general about the expected voltage under normal conditions of a correctly charged but "resting" battery.

Popped round the workshop/yard today and measured the voltages on the cars here at present. All are on the road with decent batteries and no charging faults.

Ign off voltages were 13.03, 13.01, 12.87, 12.72, 12.85.

As 1 volt can mean a great deal in battery condition I am still surprised at a "normal" resting reading of 14v, hence my comments to suspect the meter.

But if you are in the field of battery supply/research put me right.

Re: BX Charging fault-Meter is wrong! - Adrian

This site gives detailed lead acid battery performance readings for both open circuit voltage readings and specific gravities.

From the tables it does seem that 14v is excessive but your readings are slightly over too!

From what I can gather the no load voltage on a rested battery should be about 12.4v. Rested means no load or charge for at least 6 hours. The readings are also temperature dependant.


Adrians link. - David Woollard

Now and again someone points to a site which gives an excellent detail on a specific topic. was such a site. I think we should all read it at least twice before posting any more on this subject.

I think the slightly excessive voltages I've recorded (about .3v over) would be due to the batteries not having been rested for the 6hrs plus as advised, they were all on cars that hed been run within the previous few hours and this time of year batteries are at their best.

Interestingly I have tested the voltage on my own car that hasn't been started for ten days and that is 12.62. Exactly the 90% charge figure.

All good stuff.


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