On 5/06/2012 9:52 p.m., Dave Plowman (News) wrote:
In ,
Gib wrote:
While testing things I noticed my battery voltage was very high (I'd
just been running the engine). With the engine running the charging
voltage is about 19v. A new, probably more serious, problem. It's a
bit of a coincidence, so I'm wondering if they are linked. Could the
high battery voltage have caused the motor to fail? I'm familiar with
low or no voltage from the alternator, but I don't know what can cause a
high voltage.

Assuming your DVM hasn't failed - it is reading some 12.5v from the
battery with the engine stopped? - the alternator regulator has failed.
This is usually internal to the alternator but can be replaced for about
£30 if you can be bothered finding one.

Unless the rear wiper was in use for a long period, it's unlikely this
high voltage will have caused it to fail.


More interesting battery behaviour. After another day I checked the
voltage - still at 17.8v. It doesn't seem a good idea to leave it at
this level, so I turned the headlights on. The voltage dropped steadily
to about 12.8, then rose again to 13.7, then slowly fell again. After
about 10 minutes it was down to 10.3. I turned the lights off, and it
came back up to about 14.5v. I've now put the interior lights on, with
the aim of slowly pulling the voltage down to about 13 v. This was a
fairly young battery, but I guess it may be buggered by now. When I
have some spare time I'll probably pull the alternator and have a look
at the regulator - I usually can't resist getting involved in
time-wasters like this.