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Finn Lassen wrote:
This sentence
doesn't make sense: "If my crowbar overvoltage opens the B+ circuit..."
Crowbar shorts a circuit to ground. A relay or contactor allows a
circuit to open.
The relay could be in line with the wire to the field winding (handling
just a few amps) or in line with the B+ wire (output from alternator).
The crowbar typically shorts the field lead to ground, popping its CB
or blowing its fuse.
The "field" lead actually controls the B+
relay. Short it to ground, blow the fuse and the relay opens isolating
the alternator.
The problem with all this is that these safeguards introduce failure
modes of their own:
The crowbar can be triggered by a brief spike and short the voltage to
the field winding.
True. If you design it that way. I've heard
of no "false positives" around the system I use.
The contactor can stick closed (on) or open (off), and of course uses
continuous power to stay closed and adds weight and cost.
True. But I've never heard of that happening
(starter relays - yes; master relays - NO)
If one or all of the main rectifier diodes in the alternator shorts
out, you will have an alternating current (voltage) feeding the battery
and other loads. I sure hope that the "overvoltage" detector will
recognize this and kill the voltage to the field winding or disconnect
the wire from the B+ terminal.
I'm not sure that ANY OV protection devices
will detect failed diodes. Which one have I missed?
I suspect that the regulators in our alternators are very reliable,
providing they are adequately cooled. That would be one advantage for
having a external regulator: it can be mounted in a cooler location. On
the other hand, I don't know how reliable those "cheap" ford regulators
are...
Looking at the automotive industry in general,
I'm confident that they design their regulators to perform adequately
inside the alternator.
It sure would be nice with some real world info from an alternator
repair shop as to what are the most common failure modes of the
alternators we use.
I could quote you song and verse back when I
was in the business. Things might have changed in the past 25 years,
but not a whole lot I would suspect. I am pretty sure that rebuild
shops just field strip the units and rebuild. They're not in the data
gathering business, so they don't spend valuable time exploring failure
modes. They know about them, but I've never run into one that had any
better statistical data than I could pull out of my ass from my
experience 30 years ago.
I'm having a feeling of deja vu. Haven't we discussed this already?
Yup. No definitive answers then either IIRC.
Finn
Jim Sower wrote:
If my crowbar overvoltage opens the B+
circuit, there's NO current flowing out of the alternator. Absent
current, there can be no heat generated. The field can go to max
output, there will be high voltage at the B+ terminal, but no heat
generated. Sounds to me like a bogus concern. I think the key issue
is "... Nuckolls expressed dislike ..." and no further support is
"needed".
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