[Rob Edge]

From cold the battery reads 12.1 volts and drops to 11 as the pre heat comes on (2.5DT). Cranking I get 9.9 volts which seem a tad low but it starts and settles at 13.95 across the battery and 14.1 if you go from the live to earth at the alternator. Any ideas or would a new battery help. It all started when I got an ALTERNATOR FUALT message just before the stall issue in my other thread.
Thanks.
Rob.

 

[Gafferjim]

There's nothing wrong with the battery or charging system according to those voltages.

 

[jamesmartin]

i would say the readings you gave were allright cranking 9 volts is about rigth and is the reason why some earlier cars has ballast resistors and 9 volt coils so that coil didnt recieve voltage drop during cranking,you cant rule out intermittent fault ,ive had to drive with meter plugged to check charging while driving before

 

[Datatek]

I'd be a bit suspicious of 12.1 volts overnight, that's borderline flat.

 

[jamesmartin]

why all batteries i check are at a little over 12v,the depth of current is a different matter,i think dynamic test would help to check for stability modern vehicles are reliant on steady voltage

 

[Rob Edge]

I'd be a bit suspicious of 12.1 volts overnight, that's borderline flat.

I did think it low myself. I would normally expect 12.5.

 

[stchris356]

I wouldn't worry given those readings, there a tad low but nothing to worry about.
You say you had an alternator warning message after a stalling issue, thats probably due to very low engine speed and therefore low alternator output!
Won't hurt to have your battery tested though just for piece of mind.

 

[zzr1200]

If your cranking voltage is above 8.5 volts the battery is ok, do you know the "Cold Cranking Ampage" of your battery. I'd be inclined to check the bottom connection of your fuse box under the bonnet.

I have a DT and use a CCA 1000 amp commercial vehicle battery, I still get the "Alternator Warning", now and again but only when the vehicle hasn't been used in a while.

 

[JohnP38]

From cold the battery reads 12.1 volts and drops to 11 as the pre heat comes on (2.5DT). Cranking I get 9.9 volts which seem a tad low but it starts and settles at 13.95 across the battery and 14.1 if you go from the live to earth at the alternator. Any ideas or would a new battery help. It all started when I got an ALTERNATOR FUALT message just before the stall issue in my other thread.
Thanks.
Rob.

I would say those values are borderline. Battery voltage Less than 12.5 no load is about minmum.14.2 to 14.5 across the alternator under full load at approx 2000rpm should be ok.
The P38 is very sensitive to low voltage.Especially as they age and cable and GND resistances increase.

 

[mgmayo]

i have new 105amp battery in a 2.5dt and get 12.5 overnight with 13.75 max when running. I do a lot of short journeys and regularly have a flatish battery (just about starts), I was advised that eventhough it reads near to 14v it may not be charging properly that there is a common fault in the valeo alternator therefore I was advised to fit a new brush set/regulator set - available from woodauto.com - I am holding out a bit more before doing so, could it make such a differance? I have an digital lcd voltmeter fitted permanently to monitor it. It was suggested also that the new parts would prevent the hot start issue - being blamed on low cranking speed???

 

[Derek Ward]

The voltage on charge is a bit low so the battery will not be getting its full charge. Couple that with short journeys and the effort needed to crank a diesel over and it's no surprise that it's slow turning over. You could try replacing the brushes and regulator but it could also be one or more of the diodes has gone open circuit. These can be checked when you have the alternator in bits. But check also all your connections and terminals betweeen the alternator and battery. I had a similar problem on a Volvo where it was showing low volts at the battery but it was OK at the alternator. Fault was the crimped terminal at the battery end. This was renewed and no more problems.
You could also take your alternator off and take it to an auto electrical shop to be fully tested.

(For the eagle eyed amongst you, on a previous post I said the on charge voltage should be 13.8V. Wrong. Was thinking of the float charge. Doh!)

 

[Rob Edge]

Getting it plugged in tomorrow hopefully. Should be able to report back then. Possible recon alternator and new battery imminent.

 

[mgmayo]

I have been experiencing similar problems for many months and reached a solution today.
I had regular charging voltage of 13.6v but still battery charge deteriorated with short run use after maybe a week, so I would have to trickle charge.
My eventual conclusion from other posts was that the regulator/brush set needed replacing. I found this hard to source but it is available from woodauto.
My RR is a 95 2.5dt, fitted with a valeo, so search for A13V176 or 2542126.
However i bought from german fleabay for less money. The surprise was that it was an english made part from mobiletron, part VR-VW010.
It's easy to replace, no need to remove the alternator, easy to get to by removing the back cover.
I fitted it this morning and straightaway charging is up at 14.4v So happy days hopefully. I will report back with a summary in a week.

 

[mgmayo]

Update
Running for week now with new reg/brushs. Runs at 14.3-14.5v. Batt volts in eve 12.5v dropping to 11.95 in morning. So yesterday did current test. When becm at sleep still 0.4a flow. Took out fuses in turn. When either 39 or 41 were taken out current drops to required 0.04a. Therefore left them out overnight and batt was 12.35v this morning. Will investigate boards of fusebox tomorrow after seeing how to on rangerovers.net.