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From: "Joe Hull" <joeh@PilgrimTech.com>
To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
References: <list-1846398@logan.com>
Subject: RE: [FlyRotary] Re: LED built into an ATC fuse
Date: Mon, 19 Feb 2007 08:48:55 -0800
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I think this might be the fuse monitoring schematic you are talking about...

Joe Hull
Redmond/Seattle WA, Cozy-Mazda Rotary 71hrs

> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> Behalf Of Marvin Kaye
> Sent: Sunday, February 18, 2007 11:28 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: LED built into an ATC fuse
> 
> Hi guys,
> 
> I've looked all over the place and can't find that article anywhere.
> Anyway,
> the little LED circuit I mentioned earlier is extremely simple, costs next
> to
> nothing if you buy the LEDs and resistors from Mouser or Digi-Key, and
> hooks
> up in a snap.  Since I couldn't find the article it means that I also
> couldn't
> locate the schematic... that's ok, we don't need one for something this
> simple.
> 
> The typical connection to a fuse or circuit breaker (you can use this
> circuit
> with them as well, if you have a hard time seeing which breaker has
> tripped)
> is from the positive side of the power bus to one end of the fuse (or cb).
>  The other end of the fuse, of course, goes on to the load.  The LED and
> resistor connect directly to the 2 fuse terminals.  The anode side of the
> LED
> (typically the long lead) attaches to the bus side of the fuse.  The LED
> cathode (short lead) connects to one end of a 1/4 watt 1K ohm resistor,
> the
> other end of the resistor connects to the load side of the fuse.
> 
> Here's how it works... let's assume this circuit is for a single 100 watt
> landing light and the circuit is protected by a 10 amp fuse.  When you
> turn on
> the light virtually all of the voltage is dropped across the light bulb
> because of its very low resistance (maybe 1.5 ohms... 12v / 1.5 ohms = 8
> amps).  At this point there's just about a direct short across the
> LED/resistor part of the circuit in the form of the fuse (something like
> .1
> ohm) so the current takes the path of least resistance...  just about all
> of
> it flows through the fuse,  and next to none through the LED and resistor.
> So
> the landing light is dropping 11.99 volts, and there's maybe a 8-9
> millivolt
> drop across the LED/resistor, so there's nowhere near enough current there
> to
> light the LED.  Somewhere along the line we were working on our fuse panel
> and
> accidentally put a 5 amp fuse in the landing light circuit.  We go to turn
> on
> the landing light and bango!, we blow the fuse.  (100 watts / 12 volts = 8
> amps... the fuse gives up the ghost at 5, maybe a little more.)  The
> current
> path is now through the LED and resistor instead of the fuse, so virtually
> all
> of the voltage is dropped by them and there's maybe 15 millivolts left
> over
> for the landing light, which is nowhere near enough for it to light up.
> The
> LED, however, is merrily glowing away to let you know that the fuse has
> failed.  Pretty cool, eh?  There is a catch.  If the fuse is blown or
> removed
> _and_ the circuit is powered down, (ie, the switch to the landing light is
> off) the LED will not glow.  The path through the load must be complete
> for
> current to flow through the LED and resistor.  As soon as you flip that
> switch, though, the LED will light up telling you to chech that fuse and
> life
> is good once again.
> 
> I hope some of you get some use out of this... it's probably way cheaper
> than
> other options, is quick and easy, and gets the job done.  Enjoy!
> 
>   <marv>
> 
> PS... I apologize for the basic electricity lesson to all of you who
> already
> know that stuff.  I thought someone might like the full explanation.
> 
> 
> 
> "Chris Sargent" <rv7rotary@knology.net> wrote:
> 
> """
>   Marvin mentions a great capability below in having an LED light up if an
> ATC
>   fuse trips.
> """
> 
> --
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:   http://mail.lancaironline.net/lists/flyrotary/

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