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From: "Al Gietzen" <ALVentures@cox.net>
To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
Subject: RE: [FlyRotary] Re: Charging Systems and Troubleshooting
Date: Sun, 26 Jul 2009 18:06:47 -0800
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Al,
I think his point is that the alternator is damaged by turning it on =
during
cranking and that the automobile systems eliminate that problem by not
turning the alternator on till after the start key is released.=20

Bill B
------
Yeah; I get his point, but I question its validity.  He says it damages =
the
alternator because the voltage regulator is demanding max output because =
the
voltage is drawn down by the starter - max output being the upper limit =
of
the rectifier diodes.  Yes - it will set the demand for full output, but =
my
point is that 'full' output at cranking speed is likely not even close =
to
the maximum rated output for the rectifier. =20

But I don't know what the current output is at cranking speed.  I'm =
guessing
the alternator speed during cranking is maybe a couple hundred rpm, or =
less.
That output is a function of rpm, but probably non-linear.

Al

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Al Gietzen
Sent: Sunday, July 26, 2009 12:28 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Charging Systems and Troubleshooting

Bill;

That is a very interesting read.  Would have been good to know before =
wiring
my airplane.  I didn't put in a separate switch for alternator field =
because
'Why should I - cars don't have one'.  I have a pullable breaker which I
occasionally pull when I expect to have the power on with the engine off =
for
extended periods - like entering flight plans, doing EFIS upgrades, or =
back
when I did a lot of programming of the EC2.  It hadn't occurred to me =
that
there could be increased contact resistance in the breaker causing =
higher
output voltage.

 Nor had I considered that there would be high output current from the
alternator during start.  However; I question his argument on this =
point.
How much current will the alternator put out a cranking speed?  And even =
if
it is off during cranking; the moment you turn it on once the engine is
running, it senses low voltage (from the drawdown during cranking) and =
puts
out maximum current for a short time.  Anybody have any real numbers on
this?

Al G

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Sunday, July 26, 2009 6:31 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Charging Systems and Troubleshooting

=20
This has some pretty good "how to" on troubleshooting your charging =
system.
It is based on a Piper system, but is pretty close to the Nuckolls way.
Also there was a discussion a while back about whether you should turn =
the
alternator on before starting the engine.  This has a different take on =
that
subject.

http://www.nflite.com/ChargingSystem.html

Bill B


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