540i not charging?

Okay.

Why would you do that?

Measure the voltage across the alternator when the thing is running. If you have a nice high voltage on the alternator but the battery voltage is low, start looking for fusible link and cable issues. If you don't have a nice high voltage on the alternator, replace the alternator. The regulator is built into the alternator so the two go as a unit.

How many miles is on the alternator, and what year is the car?

--scott

coz a knackered battery can make the red light come on?

will check tomorrow - thanks

it's a '98 R reg with 80k miles - is this good or bad?

Maybe, but I'd sure want to do a load test before dropping the money on a new battery. And I'd want to look at both running and idle voltages across the battery.

That red light comes on when the voltage across the battery buss drops below a preset level. It can come on because the battery is very badly failed and is pulling down the line. It can come on because the alternator is bad or the cabling to the alternator is bad. Or, it can come on because the electronics in the instrument cluster are bad and give a spurious indication.

Without knowing voltages, you know nothing about what is actually going on.

That's fairly new for an alternator failure, I would think. But it could happen.

--scott

sub 12V at idle and high speed.

it has ... the windings look (and smell!) burnt out ... makes me wonder why though?

BMW £365+, Bosch £180? , Hella £185, GS&F £135 - we're going for Hella as best compromise of cost, quality, hassle etc

and I got my £100 back on the cr&p Halfords battery ... thanks for the kick!

Steve

"Putting the sensual into non-consensual sex ..." (Not mine but wish it was,

Given that BMW don't make alternators that's a big price to pay for the box BMW put the Hella one in...

One possibility is the cooling vents being blocked with leaves, etc. If it's a water cooled one, perhaps not.

I had a Volvo 480T many years ago for which I once bought a Volvo cam belt ... the belt was in a Britax bag, in a Renault bag in a Volvo bag! ... I swear each bag cost me £10 ...

Take 'em apart and see.

The thing is, if two adjacent windings touch, it will act like a second shorted winding across the whole thing... and that shorted winding will get really hot really fast. So if the varnish gets damaged just a little in winding, or if something rubs against the inside or outside of the field coil, everything can go to hell very quickly.

It's also possible for regulators to go berserk in ways that overheat the field coil without damaging the armature windings. If that is the case you'll probably see signs of overheating on the regulator board.

The BMW one is either made by Bosch or Hella, right?

I don't mind rebuilds either, if they are actually good rebuilds done by a local rebuilder who you can deal with, rather than by a chain store. If a rebuild fails, everyone will give you a replacement... but you are still out all the time you spent changing it. I have seen some pretty horrifying things in chain store rebuilds too... they'll fix what is immediately wrong but leave old bearings in, etc.

--scott

Indeed. In the UK some are just cleaned up secondhand ones from breaker's yards.