Today's Message Index:
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1. 01:09 AM - Re: Alternator failure mode (John B)
2. 06:46 AM - Re: Alternator failure mode (Robert L. Nuckolls, III)
3. 06:48 AM - Re: Alternator failure mode (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Alternator failure mode |
Bob-
Is there anything worng with using the field breaker as an alternator
control switch? Why would anyone ever want to shut off the alternator?
John B
On Fri, Jul 29, 2016 at 8:43 PM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 03:33 PM 7/29/2016, you wrote:
>
> I just finished a leak check after other mx during which the alternator
> was removed. All went well except I got an over-voltage. I started with t
he
> field breaker pulled and before I even checked bus voltage just habituall
y
> reset the field. It immediately popped. Then I saw the voltmeter at 18.1
> and stable.
>
>
> 18.1 volts AFTER the breaker popped?
>
> I shut down right away. All I could think was that I put the plug on the
> alternator upside down so I checked that--turns out that's=C3=82 impossib
le and
> it was well seated. So I plugged it back in, pulled the field=C3=82 break
er,
> started the engine. Reset the breaker and everything is normal: =C3=82 I'
m
> seeing 30+ amps at about 14.5V.
>
>
> I thought PlanePower alternators were fitted
> with their own ov protection. Can you share
> a schematic of how your alternator is wired?
>
> Are you using the field breaker as an alternator
> control switch?
>
>
> Bob . . .
>
Message 2
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| Subject: | Re: Alternator failure mode |
At 03:07 AM 7/30/2016, you wrote:
>Bob-
>Is there anything worng with using the field
>breaker as an alternator control switch?=C2 Why
>would anyone ever want to shut off the alternator?
It's a legacy thing. Since day one, TC aircraft have
had crew operated controls for all power sources. First
as independent switches and more recently as the 'split
rocker' switch.
Unless you've tested all permutations of operating
conditions, sticking with the legacy systems controls
is the least risk approach. But if one can 'live' with
the potential for dealing with an in-flight anomaly
that requires a new way of dealing with things, then
using a breaker as the occasionally operated 'switch'
is a personal choice.
In this case, there appears to be an anomaly that
presented as an alternator/regulator combination
which (1) went ov and (2) failed to shut down when
the ov system operated.
So there are two questions. (1) What are the
physics that explain the observed events and (2)
rational behind a decision to go non-legacy
controls of the electrical system.
Bob . . .
Message 3
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| Subject: | Re: Alternator failure mode |
>
>Yes, the breaker is the only control. Otherwise
>the alternator comes on with the battery. I had
>the breaker pulled before start because of of some extended battery-on
tests.=C2
>
Okay . . . it would be a good lick to open the
breaker, clip an ammeter across the breaker,
battery on, engine not running. CONFIRM that
what appears to be field excitation current
is running through the breaker.
>Again, it didn't last long but it was very
>strange to see the OV and the breaker popped--I
>had to tell myself to shut down instead of
>analyze, before the magic smoke came out...
Good move . . .
Bob . . .
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