Garage bent my valves during a cambelt change - advice please

The point being made is that it fails. It doesn't just work intermittently or pack in slowly over a period of time.

Yes. My next door neighbour has been unable to drive for a few weeks due to having surgery. He got into his car to find the battery was dead. Recharged the battery and it transpired the alternator had packed up.

It depends how old the battery was, if it's over 3 years then it's not unlikely, if the alternators dying then the battery going as well isn't unusual (it's going to go hard flat, which is never good for them)

That sounds like a dying alternator. Take it to an autoelectrician & ask.

Nope, it'll be discharged to the cutoff voltage, normally 1.75V per cell. Which is still enough to run the above, but it'll collapse completelt with another couple of amphours discharge.

11.89v is usually assumed to be 0% charge. That's around 1.98v per cell. After this point, the voltage drops very rapidly.

I don't know about modern ignition systems, but "total loss" systems (with no charging) used on racing motorcycles in the past, would start to misfire heavily once the per-cell voltage dropped much below 2v, and the things would stop around a lap later :-)

Chris

Oh but it does, dear boy. In the case of my faulty reg it was intermittent. A classic case of (probably) a dry joint. Sometimes it worked normally - sometimes was turned hard on.

Any one who claims to have a degree in electronics *should* be familiar with intermittent faults like dry joints. ;-)

The rating on a battery isn't down to 0 volts, though. It's only taken down to 10.8. The point where it ought to be recharged.

Well that's 10.5, 10.8, and 11.89. Any advance? ;-)

Nope, but I'll bet there's only a few %capacity between them. At the same temp & discharge rate.

Dry joints were not what was being discussed.

They can cause an alternator to behave in the way you say it can't. ;-)