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1. 07:17 AM - Re: Re: Newbie with PM alternator feed question (Robert L. Nuckolls, III)
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Subject: | Re: Newbie with PM alternator feed question |
>
>
>I have read that for planning purposes, one should reduce the
>alternator rating by 20% - with that thought my 30A alternator would
>nominally be used as a 24A power source for continuous duty. Yes/no?
>
>
Sortof . . . There's a fundamental notion in
aircraft electrical system design that you
should have enough alternator capacity to
recharge a largely depleted battery in
60 minutes of flight. So if you've managed
to get an engine started after dragging the
battery down to 20% of capacity -AND- it's
a 17 a.h. battery, then there should be approx
9A of 'excess' alternator capacity available
to recharge a battery. If you've only got 30A
total, then your full up running load needs
to be 21A or less.
For decades, Cessna and contemporaries were
content to bolt the same 60A alternator to
all their single engine models . . . which
generally provided LOTS of excess snort.
Further, if the battery is maintained/managed
well -AND- you never launch into IFR -AND-
your engine always starts in a few blades
then the rule of thumb for 20% reserve becomes
somewhat useless.
THIS is why airplanes with smaller alternators
benefit from an accurate load analysis along
with some judiciously crafted standard operating
procedures. If you're going to launch IFR then
KNOWING that your battery capacity is sufficient
to your battery only endurance goals is pretty
important you your wife and kids.
>
>...I will do more homework and hopefully present some better, more
>complete info. Looking forward to feedback from you and the group!
If you don't have a copy of the 'Connection, you
can download a .pdf from the website . . . or
purchase a paper copy there too . . . but given
the limited capability of your alternator combined
with the electrically dependent engine, I recommend
you educate yourself in the finer details of
energy management for CONFIDANT/COMFORTABLE flight.
Then sift the pebbles and twigs out with folks here
on the List . . .
I looked at the engine website briefly but didn't
see any mention of a 50A option alternator. Can
you point me to the information you were offered?
Bob . . .
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