From: "Dennis O'Connor"
Subject: Re: (Avionics) How can this circuit produce an "inductive surge"?
Date: Fri, 27 Sep 2002 08:41:33 -0400
Organization: Posted via Supernews, http://www.supernews.com
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
There is a group that discusses this sort of thing... The Aeroelectric
Connection, which is aimed at electrical knowledge for homebuilders wiring
their airplanes... Robert Nucholls has a book out that goes into these
issues in fine detail.... He has decades of experience in aviation
electronics in ga, commercial, and military projects... Suggest that you
get his book, read it, then if you are so inclined we can discuss it
Yes, the first solid state radios were fault intolerant, but that went away
decades ago... BTW, a 28 volt (nominal)TSO'd radio has to withstand
repetitive spikes of over 600 volts for certification..
"Jim Pennino" wrote in message
> In rec.aviation.owning Peter wrote:
> > "Dennis O'Connor" wrote:
> >>Yes... Common knowledge is commonly wrong... The alternator cannot run
> >>during engine cranking and fry the electronics... Leaving the radios on
> >>during engine start up and shut down involves no more risk of
> >>than at any other time or point in flight... >>small battery at a critical time>
> > Nothing I have seen so far contradicts what you say - especially as
> > the operating input voltage range of e.g. 24V avionics is normally up
> > to about 36V (e.g. Bendix King).
> > So what is going on? I do know of several people who blew up their
> > avionics, reportedly during engine start/stop operations.
> > OK, all it takes is a dodgy connection to the voltage regulator, and
> > you might get 50V or more...
> > Peter.
> > --
> > Return address is invalid to help stop junk mail.
> > E-mail replies to zX80@digiYserve.com but remove the X and the Y.
> > Please do NOT copy usenet posts to email - it is NOT necessary.
> The inductive caused transients from things like turning off the starter
> relay can easily be thousands of volts for a short period of time; i.e.
> To make matters worse, when you turn off an inductive load such as the
> starter relay/solenoid, the polarity of the induced voltage is the
> polarity of the applied voltage.
> Back in the days of tube electronics this was not a problem. Tubes don't
> even notice such transients.
> Solid state electronics, however, can be fried in nanoseconds.
> Least you think the problem is limited to GA, the Army years ago (when
> solid state radios began to showing up) started placarding vehicles to
> turn off the radios before starting because the troops were frying
> their new radios.
> Jim Pennino