Nav Light trouble shooting

[RLCarter]

If your reading the temp of the bulbs, the colored lens will make the temps different as will the age of the bulb, a short between the CB and the load (lights) would cause a voltage drop resulting very dim lights. Measuring the temp of CB it self will prove that it's getting hot and tripping which you already know. A multi-meter (VOM) will tell you what's going on, high resistance across the terminals of the CB = bad CB, if the CB checks good then look for a short, electrical trouble shooting requires a basic understanding of OHM's Law. The CB is mechanical and the most likely to fail due to the bi-metal spring getting weak, carbon tracks on the contacts, corrosion on the contacts or a combination. To verify a bad CB swap it with a non-eventual one with the same rating, same issue on the same circuit = bad circuit, problem changes its the CB

[Shadrach]

I understand what I need to do. My multimeter was not functioning due to a low battery and I did not have a single 9V to replace it.  I hit the bulbs with the IR because I was worried about heat build up with no air flow.  The green bulb registered 322df. The red and white were both ~100df cooler.

[RLCarter]

I understand what I need to do. My multimeter was not functioning due to a low battery and I did not have a single 9V to replace it.  I hit the bulbs with the IR because I was worried about heat build up with no air flow.  The green bulb registered 322df. The red and white were both ~100df cooler.

I have no idea what they should be, but that seem like a big difference, maybe the wrong wattage bulb?

[N601RX]

If it's the breaker which it most likely is if there is good connectivity to it the resistance change in it is going to be minimal since it last 15 minutes before tripping. It's unlikely you would be able to measure the resistance difference with a 2 lead handheld meter. You would likely need a 4 wire kelvin milli ohm meter to see the small change.  The klaxon catalog shows the thermal curves and max voltage drop. Your best bet may be to measure the voltage drop across the 2 screw terminals and compare it to the book values if you want a test to determine if it is bad. 

Edited October 8, 2015 by N601RX

[carusoam]

IR could be thrown off by different lens colors.  They are susceptible to different colored surfaces and different textures.  

If the bulb is really 100°F different than the other, the base will be hotter as well.  Measure the temp of the identical bases.  A TC based thermometer should work here as well.

If one bulb is really hotter than the other...

Is it possible that a strange (6v) bulb got installed? (Check the part number).

Best regards,

-a-

 

Edited October 8, 2015 by carusoam

[Shadrach]

IR could be thrown off by different lens colors.  They are susceptible to different colored surfaces and different textures.  

If the bulb is really 100°F different than the other, the base will be hotter as well.  Measure the temp of the identical bases.  A TC based thermometer should work here as well.

If one bulb is really hotter than the other...

Is it possible that a strange (6v) bulb got installed? (Check the part number).

Best regards,

-a-

 

negative on the 6V unless someone did it without my knowledge. We have a good supply of all needed bulbs in our hangar and overnight travel tool kit. I know the thing was super hot because I inadvertently touched it. I've a nice 1st degree burn on my thumb pad.

[carusoam]

Check the resistance of the bulbs.  The hotter one will be less resistance.  Less resistance will allow more amps to flow through the circuit, tripping the CB.

If this is the case, the hotter bulb should be somewhat brighter than usual, and may not last as long as usual.

It would be really advantageous to have a Fluke meter with a current measuring 'clamp'.  Find out how much current really is flowing through that CB.

Things to consider,

-a-

[Shadrach]

What's the easiet way to load the CB once it's removed? I think it would be easier to remove the switch and test it befor seeking out a short. Anytime something fails on the first flight out of annual, I skeptical that it's just wear and tear.

Edited October 9, 2015 by Shadrach

[carusoam]

Since it is out of the panel, did you get a good resistance measurement on the CB itself?

Setting up a current test through a plane's CB is outside of my realm.

But, in my old non-aviation lab...

Do you have any variable resistors like a dimmer switch?  Or variable voltage source like a variac(?)

Best regards,

-a-

[N201MKTurbo]

Testing it in the airplane as I said earlier is going to be your easiest option. Otherwise you will need current controlled power supply or the rarer controllable electrical load.

I have all that equipment at work and I can do a complete analysis of your breaker if you can send it to me and wait a week or so. But that would be silly, when all you have to do is disconnect one wire connect a handheld meter.

[N201MKTurbo]

Also, measuring the resistance of an incandescent bulb is not going to tell you anything useful. The resistance of a bulb filament changes significantly between cold and hot. The temperature change of a filament is much more then most people think. They are typically around 3000K (2727 C or 4940 F) The only way to accurately measure the resistance of a bulb is to measure its current and voltage drop and calculate its resistance.

You may notice a lot of lighting these days specify a color temperature. That temperature is the absolute temperature of a piece of tungsten like a bulb filament. 

[N601RX]

What's the easiet way to load the CB once it's removed? I think it would be easier to remove the switch and test it befor seeking out a short. Anytime something fails on the first flight out of annual, I skeptical that it's just wear and tear.

Do you have another breaker of the same size that goes to something else?  If so just swap the wires and see if the problem follows.  The easiest way to load it up out of the plane would be to connect a few small bulbs to it assuming you have limited access to test equipment. Just put enough bulbs in parallel to get your desired load.  The klixon catalog then gives the trip time range for load/temp.

[Shadrach]

Do you have another breaker of the same size that goes to something else?  If so just swap the wires and see if the problem follows.  The easiest way to load it up out of the plane would be to connect a few small bulbs to it assuming you have limited access to test equipment. Just put enough bulbs in parallel to get your desired load.  The klixon catalog then gives the trip time range for load/temp.

ding ding ding ding ding! Why didn't I think of that! 

Edited October 9, 2015 by Shadrach

[N601RX]

Partial shorts in non semiconductor circuits are very rare but non impossible under the right conditions (would most likely involve liquids).  If you suspect this just remove all the bulbs and turn on the switch.  If you don't want to remove a wire and hook up an amp meter or have a clamp on meter available then just use you multimeter on the low mv range dc.  Turn on the cb and measure  the voltage drop across the two screws on the cb.  It should be zero with the bulbs removed.  If it's not then there is a partial short somewhere which is very rare.  By contrast the voltage drop across the cb under its full rated load will be about .5 volts.

[PaulB]

I had a similar problem with my nav lights about a year ago. Ended up being a short in a wire somewhere behind the panel and it fixed the problem.

[Glenn]

I had the same experience, right after an annual, a number of years ago.  It turned out that the plastic trim near the pilot's side foot-well had been removed and replaced.  A self tapping screw (pointy), meant to hold the panel in place, had penetrated the wire harness that was routed out to the left wing. Vibration caused an intermittent short.   Good luck. 

[Shadrach]

OK so none of the other Klixons were of the same amperage, so I could not swap to see if the issue followed the switch.  I elected to get new PMA'd  PSA Paddle lamp Red and Green LEDs.  The cost to upgrade to those was roughly the same as a new Klixon CB switch. I hope the switch can handle the .24 amps that these draw along with the incandescent tail light.

[N601RX]

OK so none of the other Klixons were of the same amperage, so I could not swap to see if the issue followed the switch.  I elected to get new PMA'd  PSA Paddle lamp Red and Green LEDs.  The cost to upgrade to those was roughly the same as a new Klixon CB switch. I hope the switch can handle the .24 amps that these draw along with the incandescent tail light.

Are these really a PMA part? According to the manufacturer they are not.