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inrush limiters for landing lights

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sportav8r(at)gmail.com
Guest

Posted: Fri Jan 19, 2007 10:56 am Post subject: inrush limiters for landing lights

Bob-



what's you latset thinking about using inline inrush current limiters

for those of us with halogen 100w landing lights?  I'll be using mine

in wig-wag mode most of the time, and read your archived comments

about filament cooling in half-second time frames.  Will limiters help

the life of my toggle switch enough to matter?  I'm not using a relay

for that load when in the constant-on mode.



Thanks,



-Bill B.

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rv-9a-online(at)telus.net
Guest

Posted: Fri Jan 19, 2007 1:26 pm Post subject: inrush limiters for landing lights

Bill:  I have some experience with this.  The inrush limiters will save 

wear and tear on your switch, breaker and lamps.  Cold lamps have very 

low resistance, and the inrush current can exceed the switch or breaker 

rating as well as thermally shock the lamp filaments.



However, in wig-wag mode the lamps take longer to come up to full 

brightness.  I modified my wig-wag flasher to increase the flash period 

(decrease the rate) so that the lamps will come on fully.



This simply requires the replacement of a capacitor in the flasher, and 

it's readily availabe from Radio Shack.  Just look at the value that's 

in there and double it to start with.



Vern Little, 9A



Bill Boyd wrote:

 	  Quote: 	
		   

 

 Bob-

 

 what's you latset thinking about using inline inrush current limiters

 for those of us with halogen 100w landing lights?  I'll be using mine

 in wig-wag mode most of the time, and read your archived comments

 about filament cooling in half-second time frames.  Will limiters help

 the life of my toggle switch enough to matter?  I'm not using a relay

 for that load when in the constant-on mode.

 

 Thanks,

 

 -Bill B.

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nuckollsr(at)cox.net
Guest

Posted: Tue Jan 23, 2007 6:15 am Post subject: inrush limiters for landing lights

At 01:53 PM 1/19/2007 -0500, you wrote:



 	  Quote: 	
		  



Bob-



what's you latset thinking about using inline inrush current limiters

for those of us with halogen 100w landing lights?  I'll be using mine

in wig-wag mode most of the time, and read your archived comments

about filament cooling in half-second time frames.  Will limiters help

the life of my toggle switch enough to matter?  I'm not using a relay

for that load when in the constant-on mode.


	


    The whole idea behind inrush limiters grew from our

    experiences with basically automotive incandescent

    lamps adapted for use on airplanes. The 4509 sealed

    beam bulb popular on many early landing light installations

    was listed in the industrial lamp supply catalogs as

    a "tractor headlamp". The technology of 1930 was hard

    pressed to perform well on tractors, much less airplanes.

    These bulbs were not stellar performers in some

    aircraft installations . . . especially those where

    the lamps were in the cowl right under the propeller

    shaft.



    We began considering in-rush limiters at LearJet in

    the early 80's on the GP-180 program. We did figure

    out a way to incorporate a limiter into the taxi lamp

    fixture mounted on the nose gear. Unfortunately,

    I was unable to stay connected with that program so

    I have no first-hand knowledge of the value of adding

    that feature . . . and for a single installation on

    only one airplane, I'm not sure the value would have

    be obvious.



    In years hence, the generic incandescent got some

    boosts in performance when the halogen lamps hit the

    market. These lamps had inrush levels that were

    higher still but they were also MUCH more rugged

    mechanically in both automotive and aircraft

    applications. The notion of adding inrush limiting

    for the purpose of increasing lamp life sort of

    lost its glow.



    However, there were control switches to consider

    along with a mild desire not to put funky noises

    onto the bus. Here, incorporation of an inrush

    limiter would bring the first-current at turn-on

    down from perhaps 70 amps to around 20 amps. Not

    a bad thing to do . . . but really worth it?



    Consider that switch ratings are based on tens

    of thousands of operations. How long will it take

    you to put even 1000 operations on your landing

    light switch. Consider also that most switches die

    in small aircraft not from electrical and usage

    stress but from effects of age. I'll suggest

    that if we did a controlled study of the benefits

    of adding inrush limiters to all the landing light

    circuits on all GA aircraft and carefully tracked

    lamp and switch life . . . we would find that

    many other stronger factors affecting service

    life are so strong as to hide the benefits of

    inrush limiters.



    Noises on the bus? Yes, we can reduce the noise

    from that source by incorporation of an inrush

    limiter scheme be it a thermistor or keep-warm

    system. But as it turns out, the amplitude and

    duration of an incandescent lamp turn-on transient

    is less than that of a starter motor . . . for

    accessories designed to live in the real world

    of vehicular DC power generation and distribution

    have no operational problems dealing with it.



    The question was raised here on the list a few

    years ago about incandescent lamps in wig-wag

    systems. It seems logical that if each turn-on

    event generates a transient, that a succession of

    transients would result from the alternate flashing

    of two lamps in wig-wag fashion.



    Lost a trace I did on this issue some years ago

    so I went to the bench and collected this image:



http://www.aeroelectric.com/Pictures/Curves/Wig_Wag_Currents.jpg



    Note that the lamp DOES produce a cold-start

    inrush transient for first closure event but

    that the filament does not cool sufficiently

    to generate a significant transient on

    subsequent events.



    Keep in mind also that inrush limiters are

    thermal devices with long time constants too.

    They BENEFIT only while cold. If you had one in

    your wig-wag circuit, it's very low warm-

    resistance would not vary significantly between

    lamp flashes. I.e, and inrush limiter needs to

    cool for perhaps a minute before it's benefits

    can be realized for the next switch closure.



    Bottom line is that inrush limiters are of marginal

    benefit in modern lighting circuits. Rev 12 of the

    'Connection will remove recommendations for keep-warm

    and/or inrush limiters. It's an idea that has gone the

    way of spats and buggy-whips.



    Bob . . .

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sportav8r(at)gmail.com
Guest

Posted: Tue Jan 23, 2007 10:01 am Post subject: inrush limiters for landing lights

Thanks for the well-reasoned reply, Bob.  You even anticipated my

question about wig-wag contact life, etc.  I'll omit the limiters from

my wiring.



I was puzzled to see my other question appear on the list 2 full days

after I posted it- the one about the SD-8 alternator wiring... must've

been some slow-moving electrons on the information superhighway this

weekend.  Forgive my impatience for an answer to a question- I assumed

that the posting had hit the List within minutes on Saturday, but in

fact it was 10:01 pm last night when it finally sprang up.  Anyway, I

went on with other wiring tasks last night.



I'd still like to hear what is best practice for the SD-8 system.

Like I said, it's confusing when the manufacturer pigtails the dynamo

with potted 16 gauge wire for all leads, but then specifies 14 AWG by

the user, and the 'Connection Z-diagrams show the use of 12 AWG.  Even

the PIDG terminals supplied with the capacitor and regulator by B&C

are 18-22 AWG red ones <head-slap!>.  Put me out of my misery, here

  I still have the whole fuselink/ANL decision to make depending on

wire gauge selected.



-Bill



do not archive



On 1/23/07, Robert L. Nuckolls, III <nuckollsr(at)cox.net> wrote:

 	  Quote: 	
		   



 At 01:53 PM 1/19/2007 -0500, you wrote:



 >

 >

 >Bob-

 >

 >what's you latset thinking about using inline inrush current limiters

 >for those of us with halogen 100w landing lights?  I'll be using mine

 >in wig-wag mode most of the time, and read your archived comments

 >about filament cooling in half-second time frames.  Will limiters help

 >the life of my toggle switch enough to matter?  I'm not using a relay

 >for that load when in the constant-on mode.



     The whole idea behind inrush limiters grew from our

     experiences with basically automotive incandescent

     lamps adapted for use on airplanes. The 4509 sealed

     beam bulb popular on many early landing light installations

     was listed in the industrial lamp supply catalogs as

     a "tractor headlamp". The technology of 1930 was hard

     pressed to perform well on tractors, much less airplanes.

     These bulbs were not stellar performers in some

     aircraft installations . . . especially those where

     the lamps were in the cowl right under the propeller

     shaft.



     We began considering in-rush limiters at LearJet in

     the early 80's on the GP-180 program. We did figure

     out a way to incorporate a limiter into the taxi lamp

     fixture mounted on the nose gear. Unfortunately,

     I was unable to stay connected with that program so

     I have no first-hand knowledge of the value of adding

     that feature . . . and for a single installation on

     only one airplane, I'm not sure the value would have

     be obvious.



     In years hence, the generic incandescent got some

     boosts in performance when the halogen lamps hit the

     market. These lamps had inrush levels that were

     higher still but they were also MUCH more rugged

     mechanically in both automotive and aircraft

     applications. The notion of adding inrush limiting

     for the purpose of increasing lamp life sort of

     lost its glow.



     However, there were control switches to consider

     along with a mild desire not to put funky noises

     onto the bus. Here, incorporation of an inrush

     limiter would bring the first-current at turn-on

     down from perhaps 70 amps to around 20 amps. Not

     a bad thing to do . . . but really worth it?



     Consider that switch ratings are based on tens

     of thousands of operations. How long will it take

     you to put even 1000 operations on your landing

     light switch. Consider also that most switches die

     in small aircraft not from electrical and usage

     stress but from effects of age. I'll suggest

     that if we did a controlled study of the benefits

     of adding inrush limiters to all the landing light

     circuits on all GA aircraft and carefully tracked

     lamp and switch life . . . we would find that

     many other stronger factors affecting service

     life are so strong as to hide the benefits of

     inrush limiters.



     Noises on the bus? Yes, we can reduce the noise

     from that source by incorporation of an inrush

     limiter scheme be it a thermistor or keep-warm

     system. But as it turns out, the amplitude and

     duration of an incandescent lamp turn-on transient

     is less than that of a starter motor . . . for

     accessories designed to live in the real world

     of vehicular DC power generation and distribution

     have no operational problems dealing with it.



     The question was raised here on the list a few

     years ago about incandescent lamps in wig-wag

     systems. It seems logical that if each turn-on

     event generates a transient, that a succession of

     transients would result from the alternate flashing

     of two lamps in wig-wag fashion.



     Lost a trace I did on this issue some years ago

     so I went to the bench and collected this image:



 http://www.aeroelectric.com/Pictures/Curves/Wig_Wag_Currents.jpg



     Note that the lamp DOES produce a cold-start

     inrush transient for first closure event but

     that the filament does not cool sufficiently

     to generate a significant transient on

     subsequent events.



     Keep in mind also that inrush limiters are

     thermal devices with long time constants too.

     They BENEFIT only while cold. If you had one in

     your wig-wag circuit, it's very low warm-

     resistance would not vary significantly between

     lamp flashes. I.e, and inrush limiter needs to

     cool for perhaps a minute before it's benefits

     can be realized for the next switch closure.



     Bottom line is that inrush limiters are of marginal

     benefit in modern lighting circuits. Rev 12 of the

     'Connection will remove recommendations for keep-warm

     and/or inrush limiters. It's an idea that has gone the

     way of spats and buggy-whips.



     Bob . . .

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