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From: "Peter Gottlieb"
Subject: Re: (Avionics) How can this circuit produce an "inductive surge"?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 27 Sep 2002 18:42:32 GMT
NNTP-Posting-Date: Fri, 27 Sep 2002 14:42:32 EDT
There is a MAJOR difference when you wire directly to the battery - no IR
drop in the wiring to cause noise, and no inductance in the wiring for di/dt
As for the alternator running away, first this is very rare, and second, it
would have to boil the battery dry before the voltage got to levels that
would damage the avionics.
Now, if you switch the battery off in a plane and run just with the
alternator, you are at the mercy of the dynamics of the alternator regulator
and the inductance of it as a voltage source during changing loads, plus if
it decides to run away there is no battery to slow it down.
"Dennis O'Connor" wrote in message
> As a ham radio operator I have radios in my vehicles that are wired
> to the battery and are left turned on 24/7 with multiple engine starts and
> shutdowns per day... In recent decades, the radar detector is also left on
> 24/7... In over 40 years of mobile ham radio operations I have never had
> radio damage, none of my fellow hams have ever had radio damage, that I am
> aware of, attributable to the generator (in the early days) or alternator
> the vehicle..
> Tens of millions of vehicles are on the roads every hour of the day and
> night... When is the last time you saw a vehicle with its electronics
> due to alternator run away? (not heard about third hand from some guy -
> actually have laid your own eyes on) Given the hundreds of thousands of
> vehicles you have passed on the roads in your lifetime you would have had
> personally seen them if they were statistically likely... You haven't...
> Old wives tales, never seem to die..
> "Peter Gottlieb" wrote in message
> > Many cars shut off all "accessory" loads during start. There are two
> > reasons I can think of for this:
> > 1) Reduces battery drain during cranking to maximize cranking speed.
> > 2) Reduces chances of damaging spikes getting to sensitive electronics.
> > "Tarver Engineering" wrote in message
> > news:firstname.lastname@example.org...
> > >
> > > "Dennis O'Connor" wrote in message
> > > news:email@example.com...
> > > > Yes... Common knowledge is commonly wrong... The alternator cannot
> > > away
> > > > during engine cranking and fry the electronics... Leaving the radios
> > > > during engine start up and shut down involves no more risk of
> > overvoltage
> > > > than at any other time or point in flight... load
> > on
> > > a
> > > > small battery at a critical time>
> > >
> > > In fact, all three electronic dash automobiles I have owned switch out
> > their
> > > "avionics" when starting.
> > >
> > > John
> > >
> > >
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