Today's Message Index:
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1. 08:12 AM - Re: Z101B Aux Alternator and Overvoltage protection (Robert L. Nuckolls, III)
2. 08:14 AM - Re: Z101B Aux Alternator and Overvoltage protection (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Z101B Aux Alternator and Overvoltage protection |
At 08:36 PM 1/20/2021, you wrote:
><panelsonms@hotmail.com>
>
>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.
Not recommended. There's no good argument for an automatic
changeover. That feature was incorporated into the B&C LS
series regulators in anticipation of STCs onto tC aircraft.
In this case, automatic changeover WITH annunciation and
LOAD shedding advice was attractive to the spam can
crowd.
Main alternator failure is NOT an event requiring
split second detection and action. When the low volts light
comes on you can finish your cup of coffee, fold up the
map, then turn on the aux alternator and turn off the main
alternator field supply . . . load shed in accordance with
your plan-B protocols . . . then pour another cup of coffee.
Automating any part of this increases complexity and truncates
constellation of regulators suited to task (Z101 as published
can use ANY regulator/alternator combo).
>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.
>
>The solutions I can think of are:
>* Enable the aux alternator only in case of main alternator failure.
>* 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.
>* 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.
>
>Note: My aux alternator is a BC410 with an LR3C regulator.
>
>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
It's not a 'problem' . . . as you've correctly
deduced, the aux alternator of any style and
companion voltage regulator can be left in
standby readiness with a low probability of
ever being needed.
I wouldn't even put ov protection on the aux
alternator. It's pre-flight tested and known
to be functioning properly. It's only in service
for a most . . . a few hours to comfortably terminate
a flight with main alternator down. The changes of
have a dual failure (main alt + aux regulator)
during any given tank full of fuel is essentially
zero. In the well maintained airplane, the aux
alternator should have no more than a few hours
service over the lifetime of the airplane.
It's primary purpose is to REDUCE the size of
battery you need to carry to meet endurance goals.
Keep it simple. Write your own plan-b procedure
for aux alternator failure. Note that Z101
manages the WHOLE system on three switches . . .
switches unlikely to be mis-positioned in
a way that increases risk.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 2
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| Subject: | Re: Z101B Aux Alternator and Overvoltage protection |
>IIRC, the B&C regulator that's made for the
>backup alt is supposed to ignore an OV event
>caused by the main alt, and not react to OV except from its own alt.
>
>Protection for the B-lead would be the same
>whether the fuse (or breaker) is on the fat wire
>tie point, or on a bus. The fuse/CB=C2 is
>protecting the wire from the battery; not the alternator.
Correct . . . but I perceive no good reason for
adding the complexity of a full-up alternator
controller to the aux alternator system.
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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