charging voltage help

[nelo]

hi folks well another problem i think from past exp on other cars my alt may be dead or dying battery is new bosch S5 but only seeing 13.4v on the dash display have checked with my meter as well and i am getting the same reading
could anyone advise if this is correct for the car or should be 14.4v at idle as most other cars ive had ?


thanks in advance
lee

[X5Sport]

14.4V is what you should see under the bonnet with a meter.

If you can park off the road then pull the bonnet catch, lock the car and come back after 4-hours.  Lift the bonnet - do not unlock the car or open anything else - and check the battery again.  It should be 12.6 or better.  If less than 12V your flattery is likely to be bad and the alternator can't fully charge it.

There have been a number of folks on here reporting issues with Bosch batteries recently.  The fail rate seems too high for a supposed quality items.  Varta are a good alternative.

[nelo]

hi x5sport ill give it a go and see what i get and let you know
cheers lee

[nelo]

I've not done anything lately but I am getting different readings ref alternator charging on the dash it's telling me 13.4v but under the bonnet I'm getting 13.9 at idle does this sound like the alt needs looking at ?
Thanks in advance lee

[X5Sport]

Under bonnet readings will be more accurate than going through all the electronics.

13.9 at idle is OK though.

[nelo]

Cheers I'll leave it as it is
Thanks lee

[kanewesley]

Bit of theory for you to help understand what's going on........
As you know, there are 6 x cells on a battery. The voltage generated by these cells is actually 2.2 volts.
Multiply 2.2 x 6 = 13.2 volts !
Voltage = pressure like water pressure in a pipe.
To push a current back thro the battery to charge it, you need 13.3 volts at least to overcome the voltage (water pressure in a pipe) coming out of the battery.
That's why the alternator regulator is manufactured to output 14.4 volts....to give adequate "voltage pressure" to drive enough current back into the battery to charge it.
You may say 13.2 volts??? but I only get 12 volts when I measure a good battery???..This is true !!
That's because each 2.2 volt cell has an internal resistance, and 0.2 volts is dropped (lost) across that internal resistance.
But upon charging, that internal resistance voltdrop still has to be allowed for hence a charging voltage of 14.4
12v for the battery, 1.2 volt to overcome the internal resistance and the other 1.2 volts to drive a current back thro the battery to charge it.
Always handy if it ever comes up in the pub quiz !!!!!

[X5Sport]

Great stuff.  Now I have another injuneer who speaks electronish for company 

[nelo]

cheers kane
i understand the battery fundamentals i think im going to change the regulator as still getting under 13.3v on idle and under bonnet getting 13.7v when all electrics turned on when running ie seats lights wipers it drops to 12.2v even when revved so i can only surmise the regulator is Kaput
could anyone advise a decent place to get one so i don't waste my time fitting a crap one only to have to do it again in 6mths time
thanks in advance lee

[nelo]

sorry forgot to ask the stupidest question is alt removal easy on 3.0D 2003 or can it be done on car providing i can make the space ?

thanks lee ::)

[kanewesley]

It'd be easier to change the whole alternator, rather than strip it down and change the regulator.
It may not be the regulator....it may be short circuited alternator windings generating a lower voltage.
You'll get one on Fleabay for around fifty quid !!

[Steamyrotter]

You can do it in situ..

Follow:-
http://xdrivers.co.uk/forum/index.php/t ... 465.0.html