The story so far:
My battery died (probably of long term undercharging)
I discovered the alternator was wired wrong, i.e. not as per the ROM.
Fixed that, and voila a stable 14.0V (above 800RPM that is).
3 days later the alternator died completely. Diagnosed as a shorted rectifier
So today I went to the local alternator parts distrubutor, And told them the
story. “Yeah, they give problems, those alternators, in jags. The engine bay’s
too hot, and it kills them”. they said. " Not a good design of alternator
either, the air doesn’t flow properly".
OK I believe that.
“We may be able to get a heavy duty diode pack”
But I ordered some replacement diodes instead(NZ$7.50ea=US$4). I ordered some
1/2" ones to replace the pissy small 10mm ones. Same rating though - 25A/200V. I
figure the bigger body will transmit more heat to the diode plates.
A careful drill out and the plates and 5 minutes with the 10ton press, and
I’m also throwing away the black plastic back cover (keeping the centre bit to
protect the brushes though), in order to enhance airflow. Asking for trouble
with exposed 12V, but too bad.
Looking at the design(?) of the alternator, the flow is from the back to the
front, the fan on the front acting as a centrifugal pump, drawing air through
the body, and past (i.e. not through) the diode plates. I can see they fry. The
hot air after leaving the unit, gets pushed back to the back by the hot air from
the radiator, to be sucked back through the alternator, getting hotter on each
I’m looking at adding a 12V ball bearing computer fan to the back of the
alternator to provide some serious air flow, ducted up from underneath.
Overkill, you say? Perhaps, but I want to kill this problem forever. Just
replace the alternator with a GM one you say? Not in this part of the world you
don’t. A Toyota or Nissan one is a possibility though. Or perhaps I’ll just
add an extra alternator, for that extra piece of mind.