Two weeks ago I parked the car and all was fine. Then 6 days later I find the battery (6 months old) totally flat (2.5 V across the terminals). I jump started the car and measured the current with a clamp meter: 30 A charge going into the battery. Voltage OK. All seems well, perhaps the missing rod on the rear hatch operated interior light switch caused it to drain the battery (but I was convinced I had put the switch on the light itself in the off-position)...

A week later, all is still fine.

Another week later, all is still fine when I leave for a 100 km (62 mile) trip. When I return, in the last couple of miles I suddenly notice the charge light come on dimly, and so do the two to the right of it(handbrake and exclamation mark).
While driving I plug a simple three LED charge tester in the cigarette lighter, and sure enough, it shows low charge.

A couple of minutes later I see the charge light flicker and suddenly go off, and the charge tester shows a normal charge. It didn't come back.
At home I test the voltage with an idling engine at the battery terminals: 14 V and at the alternator: 14.08 V. Looks okay to me.

I'm not entirely sure that the flat battery two weeks earlier and this charge light glowing dimly are related, but who knows?

If not, is this the first sign that the brushes on the alternator need replacement, or do I need to budget for a new alternator?

Yes, it sounds like you'd better check the length of the brushes. No other car problem has come close to providing the list of on road emergencies that charging failures have. Best add a voltmeter too.

When you check the brushes, use a light and a fingertip to gauge the wear in the slip rings. That would be your best gauge of whether you are close to needing a rebuild of the alternator. If your suppliers provide the sort of on the shelf rebuilds our US suppliers do (e.g. Autozone, Advance, O'Reilly, NAPA, etc.) you should look for a local rebuilder or do your own bearings and maybe slip rings.

But mostly, I think, under 500K KM, brushes are the only thing you'll need.

Depending on the year of your 240, the intermittent charging could be a crusty fuse, but I seem to remember your Polar is beyond the fuse years. It should be if you have an electronic speedometer.
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Art Benstein near Baltimore

Ever stop to think and forget to start again?

Thanks for your reply.

I had a look at the brush/regulator assembly, and sure enough:



While looking for a replacement it seems there were two sizes of slip ring used: 28 mm and 32 mm and no supplier wanting to risk me telling me which one I need.
1197311022 is the Bosch number on the current one, so a 28 mm one, then.
Those slip rings were still nice and smooth.

I'm around the corner of a shop specialised in car electrics stuff, and they do the rebuilding of alternators and other stuff themselves.

Thanks again!

Brushes used to be cheap, but lately Bosch is pricing as if made of precious metal.







The slip rings I've used were 28mm.



If you can find the matching voltmeter, here's how I've installed them. Just did one recently on a 93, and reaching the wiring is not nearly so easy as it was pre-airbag/cruise. Otherwise, chinabay has automotive voltmeters for less than the set of brushes will cost you.

https://www.brickboard.com/RWD/volvo/1438600/220/240/260/280/installed_voltmeter.html
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Art Benstein near Baltimore

Women sometimes make fools of men, but most guys are the do-it-yourself type.

Thanks, I was wondering if replacing only the brushes is possible. Now I know it is.

However, replacement brush/regulator assemblies are easy and cheap to come buy, as long as Bosch isn't the manufacturer. I found that very few shops now seem to stock the Bosch item (and indeed very pricy), but plenty of replacements.

I chose to go with what my recently discovered German parts supplier has to offer: the assy for € 12,50. I have them coming my way now.

While searching, I found a catalogue with these assemblies available in different voltages. From as low as 14 V (as with our Volvos) to as high as 14.7 V. And even adjustable ones...

Pull the voltage regulator(two screws) and check the brushes and replace if needed. Install a voltmeter (2 1/4 inch) in one of the pods to the left of the radio.