Breaker trips on landing lights

[rockit]

I have Duckworks landing lights on both wings on my rv-9a. They are the rectangular 55watt halogen type in the leading edge.
The circuit breaker was triping after 1-2 mins of use. I had a 10 amp breaker for both the lights combined. I figured it was too small. So I replaced it with a 15 amp breaker. It still trips in less than a minute.
Any ideas?

[tim2542]

55 watts / 14.5 volts * 2 lamps should be about 7.5 amps.
Since you already changed out the breaker I'm thinking you have a fault in the wiring and the breaker(s) are doing what they are suppose to.
Eliminate one wing at a time and see if you can isolate it, you probably have an unintentional ground somewhere.
Probably ought to go back the the 10 amp cb when you get done.
Good luck
Tim

[mattsmith]

Sounds like a short, try taking a ohm meter from the load side (light side) of the switch to ground, if no resistance start looking for a short. Make sure the power is off or you will be asking Santa for a new meter

[roee]

It wouldn't be a hard short to ground or the lights would never come on, and the breaker would trip immediately. I'm assuming from the original post that the lights do come on for the 1 to 2 minutes until the breaker trips? If so, then it's not a hard short. Sounds like for whatever reason you're drawing just a little bit more current than you think you are. And there are various possible reasons why.

First of all, a 55 W halogen bulb might very well draw more than the 3.8 A that Tim calculated. This bulb is likely specified for 55 W at 12.8 V, so its current draw would be 55 W / 12.8V = 4.3 A at 12.8V. And assuming the filament acts as a simple resistive load in the steady state (probably a reasonable approximation), it'll draw even more current at a higher voltage produced by your alternator, say 4.3 A x (14.5 V / 12.8 V) = 4.9 A at 14.5 V.

Also, these light bulbs are not built or tested to super tight tolerances, so I wouldn't be surprised if they vary quite a bit from one to the next.

Also, H3 bulbs come in various power ratings. Are you sure you have 55 W bulbs and not, say, 100 W bulbs?

Anyway, the advice given by Tim to isolate and test one side at a time is good advice. And I would add to that that you should also use an ammeter to actually measure the current draw. Then you'll know rather than guess what you're actually dealing with. That always helps debug a problem.

And finally, DO NOT EVER arbitrarily use a higher rated breaker just because the existing one is tripping. Remember that the breaker is there to protect the wiring from excessive current. The breaker must be rated at less than the current carrying capacity of the wire, so that the breaker trips before the wire can heat up enough to melt or to ignite the insulation. If you use a breaker whose rating exceeds the current carrying capacity of the wire, you create a FIRE HAZARD!!!

If it turns out that the normal load current of your landing lights really is just bigger than you thought, and that you really do need a bigger breaker to accommodate that normal load current, then make sure that your choice of wire gauge is also adequate for that current, and is adequately protected by the breaker.

[rockit]

Thanks for all your feedback and concern.
1. The lights do come on for around a minute or less. So it is probably not a hard short like Roee pointed out.
2. i gather from your feedback i need to check first if the bulbs are correctly rated at 55watts. if they are, i need to isolate each side and check the current draw like Tim said.
3. If the draw is indeed upto 4.9amps per side once we identify the issue than i need to replace the 15amp breaker with the original 10amp breaker.

i will let you know what i find.

[Mike S]

Ravi, is this happening on an aircraft that has been operating correctly for a while, or is this on a brand new aircraft??

Or, is this a new light setup on an older aircraft??

Basically, have the lights worked correctly for some time in the past and the problem is just now occurring?

Also, Roee is dead on with his comments about the danger of up grading a breaker without changing the wire size.

[Rosie]

My hangar-mate just installed the Duckworks lights and I know he had the exact same problem. I don't know what gauge wire he started with but he changed his wire to a bigger gauge which solved his problem (without changing the breaker). Good luck Rosie

[MauiLvrs]

Originally Posted by rockit

3. If the draw is indeed upto 4.9amps per side once we identify the issue than i need to replace the 15amp breaker with the original 10amp breaker.

Maybe or maybe not.
The breaker needed to be sized to the wire.
You may want the option to upgrade to 100W

It is a long wire run with a lot of current and may require a larger wire than you think.

While 22 gauge can carry 5 amps for a run that long, it is too small.
You want to be at at least 18 and nay be worth running 16.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2043.13-1B/$FILE/Chapter%2011.pdf


Here is a voltage drop calculator that lets yo play with wire size...
http://www.powerstream.com/Wire_Size.htm

[Doug]

Since breakers are thermally activated do check for any local heating around the breaker. In particular check for poor crimps or connections. Any high resistance will cause local heating which when conducted via the breakers terminal posts will cause premature trip.

Be careful putting your hand on the terminations, if this is the cause they can get very hot.

[rockit]

Originally Posted by Mike S

Ravi, is this happening on an aircraft that has been operating correctly for a while, or is this on a brand new aircraft??

Or, is this a new light setup on an older aircraft??

Basically, have the lights worked correctly for some time in the past and the problem is just now occurring?

Also, Roee is dead on with his comments about the danger of up grading a breaker without changing the wire size.

I purchased this aircraft a few months ago. During the inspection the lights came on and we didn't keep them on long enough. The previous owner who was the 2nd owner claims he never flew at night and was unaware there was an issue.
I believe there was always an issue since the aircraft was built but the builder or 2nd owner didn't care to correct it since they did not fly at night.
The builder is an older gentleman who finished it in 2004 and can't seem to remember much. He has lost interest in aviation.
I have found couple other small things that he let slide so I am not surprised.
No matter how good a prepurchase inspection you do, certain things only become obvious after you have owned and flown for a few hours.
I will go out to the airport tomorrow and investigate further.