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(BOEING377) wrote in
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etc) are needing overhauls these guys just keep ticking. Well, you
might fret about their initial cost, but believe me they are worth it.
You'll also get less RF noise with the brushless alts, a plus for HF
radio users.

Very well said. Thank you. I don't know where these "dock wives tales",
like hooking alternators in parallel comes from, but it's just not true.

Whether a diode shorts in one alternator, whether parallel connected or
not, the shorted diode simply melts open! The 3 phase diode bridge is
permanently connected across the monster batteries, whether the alternator
is "on" or not. Any diode that shorts is simply, internally, melted apart
by the ensuing current surge, leaving the 3-phase bridge now a 1-phase
bridge because they are connected in delta. The "bad alternator" now puts
out much less current on one phase than it did before. You'll hear it
whenever they transmit a radio as "alternator whine" at a much lower pitch
than when they have a good alternator, but a dead cell in the battery. The
remaining connection pulses the battery wide open trying to satisfy the
regulator. It never makes it.

Because the shorted diode only lasts milliseconds, before the battery's
current melts it, the other alternator is in no danger, whatsoever, and it
will simply take up the loads, if it can. The only drawback to this is
you'll not know the first alternator failed until the second alternator
failed, so it would be a good idea to put a separate ammeter shunt in each
alternator's output so you can see which alternator is pulling what load,
not just one shunt between them.

Even operating normally, one alternator's regulator will shut down first,
the one with the lowest regulator setting. No two regulators are ever
going to hold the same exact float voltage. This is fine because when the
system reaches this float voltage, you won't need both alternator,
anyways....

Larry

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