On 10/03/2020 10:44, Dave Plowman (News) wrote:
In article ,
Tim Lamb wrote:
Ha! Just been there.
Ancient tractor with no ignition warning light at start up. Initial
investigation found ample carbon left on alternator brushes so assumed
the fault was elsewhere.
Not so:-(
The alternator slip rings were worn down to the underlying insulation
leaving a narrow strip of copper either side.
As a temporary fix, refacing the brushes regained contact and the system
is temporarily working.

Seems odd the copper wearing faster than carbon but maybe this was a
recon alternator.

I've fixed quite a few alternators over the years, and never seen severe
slip ring wear. Perhaps the operating conditions of a tractor were the
reason - the fan in the alternator passes air through it. And dust etc
could cause more wear.

IMHO, 90% of alternator faults can be sorted by a new regulator.
Mechanical wear - except at a massive mileage - pretty rare here. The
other about 10% a failed diode, fixed by replacing the pack.


Certainly the alternators I've seen fail it has been either the diodes
or the regulator in all but one case, when the bearing failed. However,
that case wasn't even an especially high mileage car- as I recall may be
40k. I certainly wouldn't consider mechanical faults or brush wear to be
common.