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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.
Bill B
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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.
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
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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