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Automatic Headlight Hi/Lo Fallover Circuit

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nuckollsr(at)cox.net
Guest

Posted: Wed Jul 04, 2007 7:23 am Post subject: Automatic Headlight Hi/Lo Fallover Circuit

At 08:42 AM 6/29/2007 -0400, you wrote:



 	  Quote: 	
		  I'm wondering if there is a device I can install on my landing lights that 

will sense when the high beam filament has failed and automagically switch 

the current to the low beam filament.



I'm using the single source/single switch wig-wag system, as per 

<http://www.aeroelectric.com/PPS/Lighting/WigWag.pdf>http://www.aeroelectric.com/PPS/Lighting/WigWag.pdf 

pg 3.0 and have only one wire to each light.



My landing lights are a Bob Olds design and utilize dual filament 

automotive H4 halogen bulbs, one per side. I would like to have something 

(preferably home brewed - read low $$$) at each headlamp that will fall 

over to the low beam so I can double bulb life, reduce maintenance and 

save a little money.



Thanks,



Tony Kirk

RV-6A N57TK


	


   Your query reminded me of an article in progress that

   needed to be finished. I've posted it at:



http://aeroelectric.com/articles/Failure_Detection_and_Annunciation.pdf



   I'll echo Eric's admonition that automatic changeover

   for failed components is appropriate only on weapons

   systems and spacecraft. Even then, the fact that a failure

   occurred and the last can of peas has been pulled down

   off the shelf needs to be annunciated with as much reliability

   as the automatic changeover system itself.



   Adding such systems into our itty-bitty airplanes has

   a high cost of ownership and poor return on investment.

   Just because your RV wants to be a 787 when it grows up

   doesn't mean it should be burdened with things that

   even the 787 pilot (and his ground crew) would find more

   of a hassle than a help.



   Bob . . .



        ----------------------------------------

        ( "Physics is like sex: sure, it may   )

        ( give some practical results, but     )

        ( that's not why we do it."            )

        (                                      )

        (                 Richard P. Feynman   )

        ----------------------------------------

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nuckollsr(at)cox.net
Guest

Posted: Thu Jul 05, 2007 5:47 am Post subject: Automatic Headlight Hi/Lo Fallover Circuit

At 08:30 PM 7/4/2007 -0400, you wrote:



 	  Quote: 	
		  



Several turns of heavy magnet wire ~18 ga wound the length of a magnetic 

reed switch in place of the .01 ohm resistor and you could bias the FET on 

when the current flow stops.  A similar idea is used to drive the bulb 

failure indicator on some cars (Volvo, uses a Bosch module) It turns on a 

warning bulb not an FET but the idea is there.


	


   Not sure what you're referring to here . . . perhaps your

   message was truncated?



   I considered a variety of current sensing techniques for

   the article but settled on the reed switch as the simplest

   and most likely to be successfully assembled by a neophyte.

   The last few circuits I designed that included a non-contact,

   current sense feature used hall devices from Amploc. See:



http://amploc.com/HANDBOOK%204.pdf



   I use these critters a lot when I need to grab a

   medium quality current value from a wire in an airplane

   where I need to avoid cutting into it for a shunt.



   Bob . . .

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trigo(at)mail.telepac.pt
Guest

Posted: Thu Jul 05, 2007 11:59 am Post subject: Automatic Headlight Hi/Lo Fallover Circuit

 	  Quote: 	
		     I considered a variety of current sensing techniques for

   the article but settled on the reed switch as the simplest

   and most likely to be successfully assembled by a neophyte.

   The last few circuits I designed that included a non-contact,

   current sense feature used hall devices from Amploc. See:



 http://amploc.com/HANDBOOK%204.pdf



   I use these critters a lot when I need to grab a

   medium quality current value from a wire in an airplane

   where I need to avoid cutting into it for a shunt.



   Bob . . .


	


Bob



And with this critters as current sensors, which is the dedicated digital 

indicator we can use in our aircraft's instrument panel ?



Carlos

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hooverra(at)verizon.net
Guest

Posted: Thu Jul 05, 2007 3:44 pm Post subject: Automatic Headlight Hi/Lo Fallover Circuit

Bob,

    Sorry I wasn't clear. The magnetic current sense element as 

described could be applied to the circuit described by Eric and thus 

eliminating the gain block and the series resistor required to develop 

the I/R drop that is the input to the gain block. Just after sending my 

previous post I saw your sensor circuit post. So my concept was to 

utilize the reed switch to turn on the FET just as you suggest turning 

on the LED indicator. The Volvo/Bosch module is interesting in that it 

uses a bifilar winding with current from one bulb going one way and 

current from the other in a pair (say front and rear right turn signal). 

If both bulbs are burning the fields cancel and no warning. This 

eliminates the problem of triggering a warning if the lights are turned 

off or flashing. The only state that will switch the module is 

unbalanced current in the 2 coils as in only one bulb lighted.

    Ralph Hoover

    RV7A

Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckollsr(at)cox.net>

 At 08:30 PM 7/4/2007 -0400, you wrote:

> 

> <hooverra(at)verizon.net>

>

> Several turns of heavy magnet wire ~18 ga wound the length of a 

> magnetic reed switch in place of the .01 ohm resistor and you could 

> bias the FET on when the current flow stops.  A similar idea is used 

> to drive the bulb failure indicator on some cars (Volvo, uses a Bosch 

> module) It turns on a warning bulb not an FET but the idea is there.

   Not sure what you're referring to here . . . perhaps your

   message was truncated?

   I considered a variety of current sensing techniques for

   the article but settled on the reed switch as the simplest

   and most likely to be successfully assembled by a neophyte.

   The last few circuits I designed that included a non-contact,

   current sense feature used hall devices from Amploc. See:

 http://amploc.com/HANDBOOK%204.pdf

   I use these critters a lot when I need to grab a

   medium quality current value from a wire in an airplane

   where I need to avoid cutting into it for a shunt.

   Bob . . .

-- 

Ralph C. Hoover

RV7A 

hooverra at verizon dot net

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rd2(at)evenlink.com
Guest

Posted: Sat Jul 07, 2007 5:02 am Post subject: Automatic Headlight Hi/Lo Fallover Circuit

Hi all,



not sure if there was an answer to Carlos' question, could not locate one.

I'd be interested in the answer as well.



Thanks

Rumen

_____________________Original message __________________________

                  (received from Carlos Trigo; Date: 08:54 PM 7/5/2007

+0100)

________________________________________________________________


<trigo(at)mail.telepac.pt>



 	  Quote: 	
		     I considered a variety of current sensing techniques for

   the article but settled on the reed switch as the simplest

   and most likely to be successfully assembled by a neophyte.

   The last few circuits I designed that included a non-contact,

   current sense feature used hall devices from Amploc. See:



 http://amploc.com/HANDBOOK%204.pdf



   I use these critters a lot when I need to grab a

   medium quality current value from a wire in an airplane

   where I need to avoid cutting into it for a shunt.



   Bob . . .


	


Bob



And with this critters as current sensors, which is the dedicated digital 

indicator we can use in our aircraft's instrument panel ?



Carlos

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