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1. 06:42 AM - Re: Re: Newbie with PM alternator feed question (Robert L. Nuckolls, III)
2. 07:14 AM - Re: Bending copper (bus) bar (JOHN TIPTON)
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Subject: | Re: Newbie with PM alternator feed question |
At 09:24 PM 8/22/2015, you wrote:
[quote="nuckolls.bob(at)aeroelect"]
>
> (1) Is dynamo current "self limiting" a characteristic of all 3
phase PM type alternators? (dynamos?) Would gladly eliminate those
three 20 amp c/b's if not required!
the PM alternators will self-destruct if presented
with a hard short on their windings generated by
failure of the rectifier=regulator. Use in-line
fuses. One for the single phase machines, two for
the three phase machines. These need no be crew-
accessible.
Do you mean these "need to be" or "need not be" crew accessible? Why?
or why not?
Do the Failure Mode Effects Analysis: What
kind of failure would put these windings
at risk? What is the probability that system
functionality will be restored by resetting
crew accessible circuit protection after
suffering such a failure?
Suggest you review the Fuses vs. Breakers
discussions on the website . . .
http://tinyurl.com/nmwyak5
. . . I think there's a pretty good case
to be made for having NO crew accessible
circuit protection for a constellation of
reasons including.
(1) Likelihood of restoring functionality
after any righteous trip is zero. The fuse
blew because something was broke . . .
(2) Unlike the circuit protection in the
TC aircraft, any discovery of a nuisance-trip
condition in an OBAM aircraft can be quickly
FIXED . . .
(3) Crew accessible circuit protection has
little up-side. It takes up panel space and
it's a potential distraction from being pilot-
in-the-air and saving mechanic-on-the-ground
activities for later.
(4) Paying homage to the federally mandated
prohibition for unreachable protection of
'critical' hardware calls for doing your FMEA
and making minimizing single-systems critical
to comfortable termination of flight.
In cases where this is simply
not possible . . . like a one and only-one
fuel injection system, then that system needs
to be crafted with critical-item reliability
like propeller bolts . . . ten to the minus
bazillion failures per flight hour. Then,
having its breaker/fuse accessible in the
cockpit becomes immaterial.
> (2) Was planning on a 40A ANL type fuse for the 10 ga wire from
the relay to the primary bus.
ANL's and their cousins are members of the
genus "current limiter" . . . exceedingly
robust and designed to protect fat-feeders
from battery-fed, 1000A+ style faults.
There are few instances in our size airplanes
where the ANL-type devices are really well
placed. The vast majority of protection goals
are handily met with fast-fuses sized to avoid
nuisance trips. I prefer the ANL-style
device for automotive-style alternator b-leads
because of their bolt-on style mounting and
wire-termination that makes them a bit more
convenient than any of the fuse holders but
a well-considered fuse installation is never
a 'bad' idea.
What is the rated output of your altenrator?
An inline maxi-fuse of next-step higher value
would be fine and a lot less bulky.
30 Amp alternator, and I like the idea of the inline maxi-fuse versus
the ANL because of the reduced size. I thought ANL type was
preferred because of the longer response time and thus helped to
avoid potential nuisance trips?
It's true that current limiters simply do
not nuisance trip but in this case, the
maxi-fuse seems the more elegant solution.
Thanks Bob! A real treat to be able to discuss topics with subject
matter experts! My cluebag continues to fill...
You're most welcome my friend . . .
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Subject: | Re: Bending copper (bus) bar |
The copper bar is 2mm (0.08inch) - so bend cold over a not too sharp (vice) edge
Thanks
Bob (and all)
John
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=446290#446290
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