10 replies to this topic

[spitfire_bob]

my battery went dead the other day and as it was a new one i thought it colud be the alternator not working.
but have noticed that battery light on dash does not come on at all when ignition switched on even though battery is now charged
if bulb has gone does that stop alternator from working properly?
cheers
bob

[fikus01]

yep u got it! that light coming on tells the alternator to start charging!!

[pinch]

i parked my mini up for a few months, and when i started using it again the battery light didn't work for a few days, but it started working again as normal after few days. the alternator is all ok.

[Dan]

Actually I'm not sure if the alternator in the MPi is a voltage sensing type. I think its a modern single wire alternator with electronic regulation that shouldn't need a 12v input to set the ouput voltage. Anyone know for sure about it?

[Major Burkenshaw]

I would hazard a guess it would be the tradition type. I.e with ignition on the charge light is given 12v and earthed via the alternator. When the engine starts, 12v is outputed from the alternator back down the wire, putting the light out. But don't quote me

[Dan]

Yes that is how the no-charge light always works but modern alternators don't actually require that circuit as an exciter I believe, it's only there as a warning. The unit on the MPi is a very modern internally cooled type of the small case variety with an electronic regulator pack so it might be a single wire type alternator but I don't know for sure.

[spitfire_bob]

right!!
checked bulb and it ok but still no power to it when ignition key is turned to 2nd position >
when running alternator is giving off 14.35 volts(even with lights,spots,heater,hazards & fogs on) so that seems to be working BUT when i went to check volts on battery i accidently pulled the earth cable off yet the car still carried on running!!!! is this right or should car stop when earth lead disconnected?
is the little wire coming off the alternator the feed to the battery light?
hope someone can help
Bob

Edited by spitfire_bob, 12 January 2007 - 05:44 PM.

[Dan]

No the car won't stop if you disconnect the battery, it is running off its own generator remember! As long as the electrical load is lower than the alternator output all the battery does while the engine is running is re-charge itself (very simplified explaination but that's how it works). It can be very bad for the alternator to disconnect the battery with the engine running though in some cases.

The small wire on the alternator should be the no charge warning circuit yes.

Check the instrument pack plug is properly connected.

[spitfire_bob]

Hi Dan
thanks for your replies
instrument pack plug on back of dash??all other dash lights come on (oil and background light bulbs,etc) so must be ok
could fault lie with little wire connection on alternator?what voltage should that read when engine is running?
sorry for all questions but electrics baffle me
thanks
Bob

[Dan]

If the output on the alternator spade for the battery warning was at the wrong voltage (high or low) then the lamp would always be on, that's what it's for. The only way the lamp can be extinguished permanantly other than a blown bulb is if it is not connected at one side or the other. Ther plug block on the instrument pack or the printed circuit on it can cause this (the plug can be mis-seated at only one terminal or the PDB can be broken) or there could be a cut in the wire to the alternator. Try continuity checking the wire from the bulbholder in the instrument pod to the small terminal on the alternator.

Edited by Dan, 13 January 2007 - 02:01 PM.

[spitfire_bob]

SORTED
i hope!!!! small wire had a break in it so repaired that cleaned connections up re-connected and hey presto battery ligth works now!
thanks to everyone who posted on this topic
Cheers
Bob