Let me take a wild guess at this one. The alternator has three sets of
rectifiers (diodes), and normally all three sets are working, and the
electrical output to the rest of the system is relatively smooth after being
filtered by the main battery. If you blow one set of rectifiers, then it all
works pretty good, but you might see some pulsing on the 12 volt bus. The
actual voltage (13-14 volts) may appear rather normal, or it may droop a bit,
especially under load. If you blow out two sets of rectifiers, then you get the
same symptoms, only much worse. At that point, you probably are not getting
much of any charge into the battery, so you may end up with a "no start"
Go have your alternator tested, and tell them what you are looking for when
they already have the tester on the system. You can't judge much about the
viability of an auto electrical system without some meters.
On 04 Aug 2003 20:54:02 GMT, email@example.com (Robertwgross) wrote:
I second Mr Gross's hunch on this one. You can check system voltage
with a DVM set on "AC volts" with engine running & a load on the
alternator. An oscilloscope is even better. Anything more than 0.1
volts AC is trouble.
Yes, the part of the problem is the mindset of the troubleshooter. If you think
of the auto as having a purely DC electrical system, then you are missing part
of it. The power is actually generated as AC and then rectified down and
smoothed. 95% of auto electrical testing can be DC-only, but you really want to
drop an AC meter across it to see that ripple is as low as it should be. If
ripple is high, then you have either blown rectifiers or else a bad battery or
else very bad wiring.
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