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Re: A different fuse.





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From: Laurence W. Coen <lwcoen@freewwweb.com>
To: 'Reflector' <reflector@awpi.com>
Subject: A different fuse.
Date: Friday, April 10, 1998 4:46 AM

The technology used in the circuit breakers for aircraft has been around
for as long as I can remember and I remember when they invented salt.  I am
using what I believe is a better mouse trap.  What I am using is a solid
state device.  It is a positive temperature coefficient (PTC) thermistor. 
It has no moving parts, doesn't arc on interruption, acts faster on
overload and can be reset in a fraction of a second.  I have attached a
circuit diagram that shows the way I protect branch circuits.  Physically,
the two LEDs are mounted above a rocker switch.  The green LED lights when
the switch is turned on.  In the event of an overload, the PolySwitch turns
off causing the green LED to go out and the red flasher LED to flash. 
Cycling the switch off and back on will reset the breaker.  Unlike the push
button type breakers, you cannot hold this one in and set your plane on
fire.

All these goodies can be obtained from Digi-Key (1-800-344-4539)

LED flasher  LT1042  $1.25 ea.
LED 12v green  MR3451QT  $.45 ea.
PolySwitch  RUE900  $1.47 ea. (9 amp. hold, other values available)

For those of you that are using an IVO in flight adjustable props, I would
recommend you add the RUE900 device in series with the current thermal
breaker supplied by IVO.  I ran some static tests to compare the mechanical
breaker to the solid state device.  The solid state device trips quickly
enough to cause less than half the compression of the plastic stop washer. 
I ran the prop from stop to stop several times and the solid state breaker
performed flawlessly.  The supplied breaker was still in the circuit and
never tripped during the testing.  I think that is the cheapest protection
you can get for your IVO gears.

Larry
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I am not familiar with  these particular devices however, proper cb
selection for aircraft requires that the cb type should be a "trip free "
type that will not allow the flow of current even when the button is held
down , during an overload event. 

regards

Jim Glindemann