Legacy 12 smoke and fumes

I have a 2011 12 and am not the builder. Been running great until this morning. Started out with getting A/P error on start. Wouldn't reset and couldn't shut down from AP74. Eventually it did reset and everything was good. Taxied out to do run up and that's when fun began. RPM to 4000 A side off and about 120 drop. Back on and up to 4000, B side off and it dropped about and 150 and sounded kind of rough. B side back on and that's when white smoke started flowing out of panel below the rocker switches. Immediately shut and down..after grabbing fire extinguisher..just in case. The smoke continued for about 10 seconds after shutdown.
Took back to hanger and started opening things up. Found no indications of fire or heat. Upon further inspection found an oily residue under rocker switches. Since there is a large electrolytic capacitor just above that area I assumed it had failed and was leaking. I have it all apart and it doesn't seem to be bulged or leaking. Next step is dissembling and removing from the board for test.
I'm wondering if this something anyone else has had to deal with and if it's just easier to order the entire assembly. It looks like it was built by Vans as the pcb board has their imprint on it.
I'm trying to find a part number to see if it's even available. Attached are a couple of pics.
Any help or pointers would be appreciated

That part number is “AV CONTROL BOARD-12”, but unless you’re willing to shell out $850 for a new one, you might want to take a closer look at that capacitor. I’d even replace it before buying a new board.

yike...

That's the plan for now..I told the wife I would be surprised if it was less than $1000 for a replacement. Thanks for the info. I'll post what I find after testing the cap.

Crbunt said:

I have a 2011 12 and am not the builder. Been running great until this morning. Started out with getting A/P error on start. Wouldn't reset and couldn't shut down from AP74. Eventually it did reset and everything was good. Taxied out to do run up and that's when fun began. RPM to 4000 A side off and about 120 drop. Back on and up to 4000, B side off and it dropped about and 150 and sounded kind of rough. B side back on and that's when white smoke started flowing out of panel below the rocker switches. Immediately shut and down..after grabbing fire extinguisher..just in case. The smoke continued for about 10 seconds after shutdown.
Took back to hanger and started opening things up. Found no indications of fire or heat. Upon further inspection found an oily residue under rocker switches. Since there is a large electrolytic capacitor just above that area I assumed it had failed and was leaking. I have it all apart and it doesn't seem to be bulged or leaking. Next step is dissembling and removing from the board for test.
I'm wondering if this something anyone else has had to deal with and if it's just easier to order the entire assembly. It looks like it was built by Vans as the pcb board has their imprint on it.
I'm trying to find a part number to see if it's even available. Attached are a couple of pics.
Any help or pointers would be appreciated

Click to expand...

I have worked with this assembly quite a bit and this is the first time I recall that it looks like the capacitor has failed in this manor.
Another clue is that it appears that the two plastic tie wraps that were used to anchor it to the pcb, have melted.

If you pulled enough current to make smoke, and no fuses blew, then I would begin looking at circuit board traces. That much current would cause traces to heat and lift off the surface of the board.

UVR1E223MRD 22000uF Electrolytic Capacitor

I posted the capacitor number and link in this thread. DigiKey has them for less then $6.00 ea.
https://vansairforce.net/community/showthread.php?t=216874

Legacy RV-12 capacitor

There is a 30 amp fuse between the capacitor and the battery.
That fuse won't blow easily.
There is NO fuse between the capacitor and charging system

I'm sure you would have noticed, but no chance your voltage regulator took a dive and was giving > 25v to the bus? I always see electrolytic caps die first on circuit boards.. so I'm not surprised.. but am surprised that any.. even the shoddy chinesium ones would fail at (whatever your TT is)

Followup

I've ordered a voltage regulator. Just in case. The ties were cut by me to read the info on the capacitor. The traces look fine and there were no fuses blown. First thing I checked. I've ordered the replacement cap so we will see if I still have any soldering skills left to replace it. The plane just hit 500 hours. We flew it for 1.5 hours the day before with no indications of any issues. So the plan is to replace the cap Reassemble everything..all 200 screws!...and test run it. If there are any other issues then I'll probably order the entire board from Van's and go from there...I'm not getting any younger and I need to get flying!
Thanks for the input..really helps to have more people to help think things through.

I believe that Cap is for noise filtering. Rotax require one for radio interference.

bobg56 said:

I believe that Cap is for noise filtering. Rotax require one for radio interference.

Click to expand...

That's correct. I had one fail in the air just after takeoff on climb out. There was a bang and the cabin filled with smoke. I declared an emergency, turned the master switch off and landed. This was in my Kitfox IV with a rotax 912 ULS. There wasn't much left of the capacitor. I replaced the capacitor and placed the new one forward of the firewall. The original one was aft of the firewall per the kit instructions.

I bought the replacement from ACS and it was much better quality than the one that came with the kit.

Henry

Thanks

That's good to know. Fortunately ours occurred on the ground during runup..still smoke in the cockpit is a bit disconcerting.

Failed Capacitor

Here's the one that failed. Have the new one installed but haven't powered anything up yet...felt like 110 degrees in hanger and my limit is 105. I trimmed the leads off to make it easier to remove from board.

Can someone with elec knowledge say what the likely cause of capacitor failure is? Age of component, excess current, heat, temp cycles, humidity, mfgr defect, etc, etc....

Capacitor

Talked to a friend of mine who does a lot of this work and he said that mostly it's combination of heat and age. He was not surprised that it failed after being in service for 10+ years. YMMV....
Rick

Piper J3 said:

Can someone with elec knowledge say what the likely cause of capacitor failure is? Age of component, excess current, heat, temp cycles, humidity, mfgr defect, etc, etc....

Click to expand...

TL;DR

All capacitors are two metal plates with an insulator (dielectric) between them. Capacitance is proportional to the area of the plates and the distance between them. Bigger plates... more capacitance. Closer together... more capacitance.

Capacitors have several roles but when used for noise filtering bigger is better. The two ways to have more capacitance is bigger plates or put them closer together. Making them bigger has its limitations so there are several techniques for getting the plates close together and, very importantly, without touching each other.

Most large DC filtering capacitors are electrolytic capacitors. These are made with two aluminum foil sheets with an electrolyte gel between them. The insulator between the plates is a very thing coat of oxide on one of the foil sheets. The gel conducts electricity. So in effect what you have is two capacitor plates that are separated in distance by only that thin oxide coat.

So what kind of failure modes does an electrolytic capacitor exhibit? The primary type of failure is always leakage current between the plates. Remember, they are supposed to be insulated from each other.

• Mechanical damage can cause the plates to touch. Go easy on that zip tie holding the capacitor in place!
• The oxide layer is pretty thin so too much voltage can cause current to tunnel through the insulating oxide.
• Something like reverse polarity can cause the oxide layer to break down.
• Heat is always hard on electrical components. Most electrolytic caps that I have used seem to be pretty heat tolerant, though. It would be worth looking at the data sheet for the cap to see what it says about heat range.

When a capacitor starts leaking current it may get hot if there is enough current. One amp of leakage current at 12 volts is 12 watts of heat. That is more than enough to make a cap get hot. When the cap gets hot enough it explodes.

It is hard to say why your capacitor failed. I mostly worry about over-voltage because I've blown a few that way. If you have a 12 volt system don't put in a 15 volt capacitor. If you have noise spikes you may regularly have higher voltages spikes that punch holes in the dielectric oxide. Over time the damage accumulates. In a high impulsive noise environment I wonder if it would be prudent to have TVS diode in parallel to limit noise spikes to something the filter capacitor can tolerate.

One final word. I have an HVAC guy that regularly comes to the house. He pulls the compressor starter cap and "tests" it by measuring the capacitance. That never seemed like a terribly effective way to test a capacitor to me. The capacitance is set by the physics. I.e plate size and oxide thickness. Maybe if the measured capacitance goes up significantly you could say the oxide is getting generally thinner but I've never seen that happen. Instead a much better way to judge the health of a filter capacitor is to measure the leakage current and especially at what voltage you start to get significant leakage current. But that take more than just a hand held multi-meter.

Crbunt said:

Talked to a friend of mine who does a lot of this work and he said that mostly it's combination of heat and age. He was not surprised that it failed after being in service for 10+ years. YMMV....
Rick

Click to expand...

Hey Rick, Unless I missed it, I never saw a post that mentioned whether that new capasiter fixed your electrical problem or not. Would appreciate your comments. Thanks.........Tom

Fixed

todehnal said:

Hey Rick, Unless I missed it, I never saw a post that mentioned whether that new capasiter fixed your electrical problem or not. Would appreciate your comments. Thanks.........Tom

Click to expand...

It did. Sorry I thought I updated that. It was actually an easier fix than I made it. I did it the hard way and removed the entire board when I could have replaced the capacitor in place. Live and learn...
Rick