nuckolls.bob(at)aeroelect
Guest
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 Posted: Tue Dec 21, 2021 10:57 am Post subject: Z101B Aux Alternator and Overvoltage protection |
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| Quote: | | Quote: | For those with Z101B, what is your procedure for using the aux alternator? My initial thought was to turn on the aux alternator with the main alternator and use a lower voltage setpoint for the aux regulator. This allows the aux alternator to take over without intervention if the main alternator fails.
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that was a 'feel-good' feature crafted for the
TC aircraft manufacturers who were adding the
SD20 and cousins to their production aircraft.
It adds complexity and cost to the device without
materially improving safety.
| Quote: | | Quote: | This causes a different problem, however. The main regulator could fail resulting in an overvoltage condition. The crowbar overvoltage protection circuits would blow the aux alt fuse and trip the main field circuit breaker. Z101B shows the aux alt fuse forward of the firewall so it can't be replaced in flight. Essentially, an overvoltage event on the main regulator will take out both alternators.
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If memory serves, all the B&C regulators
with built in crowbar feature a field voltage
monitor loop . . . I can't remember which
model got it first but I think they eventually
all had it. When an OV is sensed, the trip
logic looks at field voltage. If the voltage
is 'high' then the logic assumes LOCAL
failure of the regulator and trips the system.
I field voltage is 'low' then the logic knows
that its companion regulator is functioning
and OV trip is INHIBITED.
| Quote: | | Quote: | The solutions I can think of are:
* Enable the aux alternator only in case of main alternator failure. |
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I would do this anyhow. There is no value
added by millisecond response to bringing the
aux alterantor on line.
| Quote: | | Quote: | | * Move the aux field breaker/fuse to the main bus so it can be in the cabin, but this removes some fault tolerance of the design. |
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Not necessary
| Quote: | | Quote: | | * Come up with an arrangement for the aux regulator that allows a slightly longer period before the overvoltage protection activates. This seems like a fragile solution though. |
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Correct. Already fixed.
| Quote: | | Quote: | | Note: My aux alternator is a BC410 with an LR3C regulator. |
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Check with B&C . . . my drawings for that product
are quite old and of uncertain validity. Inquire
as to whether the LR3C incorporates 'selective
OV trip'. I am pretty sure it does but getting
info from the source is certain.
| Quote: | | Quote: | | Interested in hearing people's procedures for the aux alt switch and/or if they've deviated from the Z101B wiring diagram to solve this problem |
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It's a problem that doesn't need solving. The aux alternator
should be off-line 99.99% of all operations. In fact, it's
duty factors are so small and it's tested every
flight cycle, I didn't even include OV protection in
Z101. Selective tripping isn't needed for independently
operated alternators. Hence, a builder could consider
a alternative alternator controller products for
either/both alternators.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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