"Miracle switch" failures

[JOddino]

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
> 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: <s.vannostrand at kodak.com>
> To: <discussion at nsrca.org>
> Sent: Monday, March 24, 2003 1:16 PM
> Subject: "Miracle switch" failures
>
>
> > I know there are some vendors and users of those voltage regulators with
> > the built in switch.  One mfg calls it the miracle switch.  I have one,
> > hooked it up, am using it with no problems so far, but I may be just
> lucky.
> > Is there a right/wrong way to hook up the connectors?  I have a radio
> south
> > one and there are two male connectors (one for the receiver, and one for
> > recharging), and one female (for the battery input).  The system works
> with
> > either male plugged into the receiver.  Based on Wayne's sad story below
> > I'm wondering if maybe only one should be connected to the receiver in
> > order to maintain voltage when the switch fails.
> >
> > Anyone know if there is a sure way to tell if you have it hooked up
> > correctly?
> >
> >
> > Wayne writes, " I am/was using a MCI Miracle switch that is a regulator
> and
> > has fail safe if the mechanical switch contacts fail the switch stays on
> > all the time.   I tested the battery and it checked at 6.5v.  I checked
> > through the charge port and 6.5v.  But when I checked it through the
> > connector to the receiver it only registered 4.25v  just below the
> > receivers voltage threshold. "
> >
> > --Lance
> >
> >
> >
> >
> > =====================================
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> > # and put leave discussion on the first line of the body.
> > #
> >
> >
>
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>

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