Strange odor

[rwarre]

When I turn on my taxi lights I smell this pungent odor similar to burning wire.
I have the Vans wingtip taxi and landing lights and my circuits are protected by fuses on a panel under the dash. Could this be a fuse problem or wire?

[wjb]

Unlikely a fuse problem ... or the fuse would have blown (or the blow point of the fuse is too high.) If you're smelling something, something's getting hot! I'd inspect the wires look for any discoloration or blistering; you may have a short to ground somewhere, or you could have a bad contact in a connector or splice that's heating up due to a higher than planned resistance.

Do the lights work as expected? What gauge (AWG) wire are you running?

You can pull the fuse, turn on the switch, and see how many amps the circuit it drawing with an ammeter ... it should be very close to the expected values based on the specs for the lights.

You can also buzz out the wires, measuring their resistance, to see if it's consistent with the wire size you're using. If the resistance is high, you likely have a bad connection, which could be getting hot.

Anything that smells of "burning wire" should get run to ground before proceeding.

[BobTurner]

On the ground, master off, use heavy duty alligator clips to carefully jumper the light switch. Turn master on. If lights come on but no smell, it's the switch or its connections that are defective.

[n82rb]

how many amps does the circuit pull? what is the switch rated for? check the switch it could be getting hot and starting to fail.

bob burns
N82RB
RV-4

[rwarre]

Upon checking out the wiring at the switch connection, I discovered that one wire got hot enough to melt the heat shrink and part of the wire insulation. I did some trouble shooting and with the help of an electronics friend, discovered that one terminal of the switch had way too much resistance. Ordered a new switch and should be good to go. Thanks for all the advice from those on this site.

[grubbat]

Now that you found the problem, spend some time and figure out why the fuse didn't blow to prevent that wire from getting supper hot.

If the switch decides to malfunction in future, you will want that fuse to blow to protect wiring and potentially your airframe.

Cj

[PaigeHoffart]

The fuse didn't blow because a high resistance connection won't cause an over current condition with most loads.

What brand was the switch? There is a long history of problems like this with Carling switches (search the archives).

Paige

[AlexPeterson]

Originally Posted by PaigeHoffart

The fuse didn't blow because a high resistance connection won't cause an over current condition with most loads.

What brand was the switch? There is a long history of problems like this with Carling switches (search the archives).

Paige

Yes, I've had this also. The switches we commonly use are not rated for the DC loads we put on them (the classic Carling ones). I've had a couple go bad - they get warm or hot. I've gotten into the habit of putting my hand on them from time to time (they are at the bottom of the panel where this is easily done).

[RV3bpilot]

Go with your gut feeling and fix it before you fly it! I have a high powered HID landing light that takes a lot of power to turn on. After it is on the power draw goes down a bit. But not one bit of smell from any wires.
I would test the amp draw of your light system to see if it has a normal load for your installed lights. My light requires big wire 14 or 12 gage, I think I used 12 gage, over kill but safe.
I'm sure you will figure it out, just be patient.

[vlittle]

Originally Posted by AlexPeterson

Yes, I've had this also. The switches we commonly use are not rated for the DC loads we put on them (the classic Carling ones). I've had a couple go bad - they get warm or hot. I've gotten into the habit of putting my hand on them from time to time (they are at the bottom of the panel where this is easily done).

The fundamental issue is not the DC rating of the switch, but the Lamp load rating of the switch. Here is a good reference that can be used in the design of any electrical system.

Typically, the switch derating is 20 to 25 percent of the steady state load. For a 10 amp landing light load, this means the switch Resistive load rating should be 40 to 50 amps.

Alternatively, inrush current limiters can be wired in series with the load to limit the turn-on current surges that damage the switches.

The worst offenders are old-style strobe power supplies and landing/taxi lights, but inductive loads (motors or pumps) can be trouble as well.

In my RV-9A, I had multiple Carling switches fail.. Master, Strobe, Landing and Taxi switches. The Landing and Taxi switches usesd inrush limiters but still were heating up due to the wigwag function.

I replaced the Carlings with Honeywell switches and everything was fine. Internal analysis showed that the Carling switches failed due to overheating and loose rivets. The Honeywell switches use solid rivets, while the Carling switches used hollow rivets for the terminals.

In my Rocket, I got rid of load-carrying switches entirely by using relays controlled by low current switches.