Another V11 FFS

On the return journey from a little trip into Cambridge this morning, I
noticed that the tacho had died. Ah well, not absolutely urgent to fix
it, I thought. I also thought I saw the telltales looking a bit dim, but
hey, it's quite bright, not a morning or evening commute.

See where this is going yet?

A mile from home, as I accelerated from a junction, the engine started
misfiring. So I hurriedly flicked off the headlight, and the engine
instantly recovered.

Ho hum. Battery's not charging. The alternator doesn't seem to be shorted
to ground or open circuit, but the output from the regulator is only
about 8V. More investigation to follow.

So that's another job to do this weekend, after replacing the car's
broken anti-roll bar linkage.

 

Check for a resistive earth first. Jump lead from battery earth to
alternator is the quickest diagnostic method.

 

Well, the first thing I tried was swapping out the regulator for a spare
(I cleaned the contacts as a matter of course): the battery didn't charge
but at least I was seeing tiny rises in the battery voltage when I revved
the engine. Also the charge warning light was lit continuously; the old
regulator wasn't showing a warning light.

The open circuit voltage of the alternator was rather low: around 19V at
idle, but it was at least fully isolated from the chassis. A failure mode
I've seen in the past was a winding shorted to a pole piece.

I next tried borrowing the Quota's alternator stator: that fixed it, so
the alternator was fucked and probably the regulator as well. I'll leave
it on the V11 for now as the Quota's Hors de gearbox.

Ho hum. Time to order another alternator.

 

Well, another twist. When I reassembled the V11 last night, I checked
the system was charging correctly: fourteen anna bit volts at various
revs. Great.

However, the charge warning light came on en route to work. Checked at
work: definitely not charging but all wiring is good.

I made the commute home, plus an emergency lunchtime run to buy a
Valentine card, all on whatever charge the battery had.

On closer inspection at home, there was a distinct smell of very hot
stuff coming form the voltage regulator and black goo had leaked out
of it. Fortunately, when I put the stator back on the Quota, despite
it also smelling a trifle cooked, it was working fine.

So I guess I simply replaced one dodgy regulator with another.