"Miracle switch" failures

[John Ferrell]

Perhaps I misread the the email.

What I understood was that there was a mechanical switch across the
electronic
switch for redundency. That was the condition that I felt risky.

The chips we have available these days are real close to magic! I had a 7805
regulator in an
antenna rotator that was left dead shorted for several days after a
lightning strike and it survived...

As far as TV tuners go, I have a Sony portable that I bought as my first
color monitor BEFORE the IBM PC that is working fine...
I believe we are sayin the same thing.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



----- Original Message -----
From: "JOddino" <JOddino at socal.rr.com>
To: <discussion at nsrca.org>
Sent: Tuesday, March 25, 2003 12:04 PM
Subject: Re: "Miracle switch" failures


> First of all the electronic "switch" is a device used in a linear mode
when
> regulating.  If the input voltage drops below the set regulated voltage it
> will saturate and if it is a good regulator will have an on resitance of
50
> milliohms or so.  I didn't hear if he checked the input voltage under the
> same conditions he measured 4.2 volts on the output.  Either the input
> voltage was low or the on resistance was high and/or the load current was
> too high.
> Second, the electronic switch/regulator is not in parallel or tandem with
> the mechanical switch.  If the mechanical switch fell off the plane you
> would not lose power.  In fact I don't even have a mechanical switch on my
> new plane.  I use a safeing plug to turn it off.
> The device I use protects itself and I wouldn't know how to make it fail
> within its rated operating conditions.  You can put a dead short on the
> output and not hurt anything.  Try that with your mechanical switch but
have
> a fire extinguisher handy.
> Think about how long the old mechanical tuners on TVs lasted.  When was
the
> last time you heard of an electronic tuner going bad?  I rest my case.
> Jim
> ----- Original Message -----
> From: "John Ferrell" <johnferrell at earthlink.net>
> To: <discussion at nsrca.org>
> Sent: Tuesday, March 25, 2003 6:24 AM
> Subject: Re: "Miracle switch" failures
>
>
> > If I understand the failure conditions, the electronic switch was
> paralleled
> > with a mechanical switch.
> > That is not something that would be considered a 'normal' configuration
> for
> > the electronic switch.
> > I refrain from using these devices because I have never had a switch
> problem
> > with a Futaba switch.
> > Most electronic power switching devices that I am aware of are MOSFET
> > technology.
> > These devices switch many amps with great reliability, but are extremely
> > vulnerable to voltage spikes.
> > The inputs and outputs are protected by internal diodes from these
spikes.
> > I have been unable to puzzle out if there is an unprotected input-output
> > junction.
> > Here is a possible scenario:
> >     The mechanical switch is turned off generating a spike that damages
> the
> > elecronic switch in a failure
> >     mode that drags down the receiver voltage feed.
> > My personal conclusion is that either switch will work as advertised,
but
> > when used in tandem it is
> > not a matter of if it will fail but when it will fail.
> >
> > John Ferrell


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