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Halogen bulbs with wig wag circuitry....failure mode

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Oct 14, 2011 11:55 am Post subject: Halogen bulbs with wig wag circuitry....failure mode

 	  Quote: 	
		  

Funny, I did not know that the halogen environment still included 

tungsten filaments.  I was assuming, some other mixture of metal was 

the basis for these brighter lamps.


	


    It's my assumption that they're still tungsten.

    A quick look at Wikipeda



http://en.wikipedia.org/wiki/Halogen_lamps



    didn't suggest any 'new' materials.



    You bring up an interesting option...to keep the lamp filaments 

in their flexible or ductile stage while in any none use state.  I 

wonder what level of current would be needed for that in a 12 - 14 v. system.



    The POWER needed is quite low but the current

    is substantial due to the large positive temperature

    coefficient of lamp resistance. I just took a couple

    14v halogen lamps to the bench and was able to get

    the first signs of visible light (tiny red glow) at

    about 1.5 volts. However, the current draw was a

    substantial portion of rated current at full voltage.

    One example: A lamp I tested gave me first visible

    light at 1.5V and 1.7A for a total of about 2.6W.

    This lamp was rated at 55W at 14V or 3.9A.



    This says that the resistor-diode technique described

    in the 'Connection would be terribly inefficient. But

    if you've got a fat alternator and some place to

    let the heat dump out . . . the technique may be

    practical . . . and low cost.



    The obvious solution is to use a 2 t0 2.5v DC-DC

    converter. There are a number of commercial off the

    shelf products. Many such devices can be purchased

    through the industrial surplus houses for a reasonable

    price. Alternatively, you can do your own DC-DC buck

    converter. There are a number of design tools

    on the 'net that will assist in component selection.

    The nice thing about it is that output ripple

    voltage can be pretty high. Light bulbs don't care.

    You WILL want to consider EMC filtering as these

    devices operate in the 0.1 to 1.0 MHz range and

    would be pretty noisy.



    The fast-turn solution might be to use an LED

    driver like the Buck Puck 2100 mA device



http://www.ledsupply.com/0a009-d-v-2100.php

    throttled down through the dimming input to

    get you a barely visible light output in a dark

    hangar. EMC questions apply here too. The neat

    thing about DC to DC conversion is efficiency.

    Something like the Buck-Puck should be 85% efficient

    or better. A 2.5 watt keep warm system for a 55w

    lamp would only need 3W or so from the bus.



    Another plus of the Buck Pucks is that they're

    rated for up to 32 volts operating voltage.

    PLENTY of headroom for observing DO-160 surge

    requirements in a 14v system.



And, an option would have to be planned in the case of an alternator 

failure to cut the background lamp current.  Thanks,



    You bet. Of course, things light landing lights

    might drive from the main bus which would be down

    during battery only ops anyhow. If you've got

    battery left over on short final, then bring the

    main bus back up and use the landing light.



    The keepwarm circuit is a great mitigation

    of inrush current too.

   Bob . . .

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skywagon

Joined: 11 Feb 2006
Posts: 184

Posted: Sat Oct 15, 2011 8:53 am Post subject: Halogen bulbs with wig wag circuitry....failure mode

....again, Bob, I appreciate the insight you gave this matter.

Some interesting results you found for the keep alive current needs being 

that the current requirement is nearly 50% of the operating current but at 

low power.  The DC to DC for the low voltage stage is an interesting 

idea....  I am going to run this next set of bulbs with the vertically 

oriented filaments and keep closer tabs on the time to failure.....

If the same short life, then it is time to use your idea or move on the next 

generation of lighting system.

 Thanks, David



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