A strong recommendation: fuse the battery charge wire

[Anticept]

This came to my attention on an airplane. I got asked to take a look. I can tell a fire started and fizzled out. The damage is severe, and will take some serious composite work in Tulsa. It's gonna be EXPENSIVE, but it should be an insurance claim at least.

 

 

This isn't the first time I've seen something like this happen. Not the second. Not even the fourth. But this is the worst I have ever seen.

 

My airplane no longer has a dangling charge wire as of last year, but before that I had run a new wire where I didn't strip the insulation off like normal, but instead I went back far enough on the wire and used a knife to trim a ring, just enough for a clamp to contact, but it was done in a way that there is no way bare metal can contact the cowl. I left insulation on the tip too, so that can't slap against the bottom and short out either. Keeps the wire from contacting the cowl.

During my retrofit with an EarthX battery and replacement with a plug, I noticed the in line fuse inches from the battery positive terminal on the harness.

As such, I have been strongly recommending people retrofit an in line fuse on their airplanes on this external charge wire. The size of the fuse has to consider your charger, and if you use a power supply mode (where it might supply power for the airplane to draw so you can play with your avionics), but around 10-15 amps is probably fine for most applications.

It doesn't matter how small your charger is, the reason this happens is the battery gets shorted to the cowl, pumping as many amps as it will allow. The carbon fiber has a pretty low resistance, so seeing a hundred amps wouldn't be a surprise. This inline fuse will prevent an accident of this magnitude from happening.

[Madhatter]

Good observation,  something I will do

[Tom Baker]

I had a customer have this happen with a CTLSi. He just got it back from Tulsa not to long ago. The dangling charge wire is gone, and a plug for the charger is accessible inside the oil door now.

[Tom Baker]

The wire is generally okay by itself, but the problem comes with the weight of the battery charger clip.

[FlyingMonkey]

I have used the charge wire exactly once, to jump start my engine.  I always take the cowl off and connect directly to the battery terminals for charging.

[Madhatter]

I suppose for as rare as it is to have to perform a jump start you could install a fuse holder with a direct terminal option. You would have to connect it to the battery if a jump start is needed. I never liked the clamp that holds the wire to the frame, seemed like a direct short waiting to happen one day.

[Anticept]

I advise against jump starting. I know people will do it anyways... but batteries are only meant to have a certain charge rate, known as 1C, for heat dissipation. I've seen a concorde battery in a piper cherokee ruined by a jump start, the battery got so hot it internally shorted and blew the safety cap.

1c = 1 hour to charge fully, if it were constant current.

A lead acid battery at half charge will take up a lot of amps. Carb engines can't push a lot though it heavily loads the charging system, but for those with an iS engine, you can pump a LOT of power into the battery and it will heat up internally pretty quick.

If you are going to need a jump, do it sooner than later so you don't deplete the battery as much.

EarthX batteries will not allow you to overcharge them, they have temperature sensors and charge regulation circuitry.

[Madhatter]

Most aircraft are designed to be started with additional external power, however not with a dead battery.  I have had instances where I needed a little extra boost in cold conditions for a twin but never on a dead battery. If you jump start on a dead battery you may find a popped main breaker on a gear retraction and you lose everything. If IFR you are toast.

[Roger Lee]

These damages can easily be caused when the positive wire under the plane touches the frame. Carbon fiber is conductive and will burn. I have seen this twice. ALWAYS keep the wire bent down away from the frame and if you use a charge make sure it is also pulled down away from the frame. The fuselage is grounded so if the positive wire touches it will cause excessive heating and fire type damage.

[Madhatter]

A thick wall piece of silicone tubing on the exposed wire end works well as an insulator. 

[Anticept]

As said, on mine, when I still had the wire, I ran a new one and only trimmed away a small ring for a charge clamp to get a little bite of. The end of it still had its insulation.

 

Re: external power: that's fine and I agree. When I refer to jump starting, it's where people are trying to force start with not enough juice on the onboard battery to do much of anything.

[Madhatter]

Not an issue anymore. Never had to jump start and wouldn't want to on this aircraft. The first sign of a slow start with everything else good I replace the battery. Nothing worse than being on a cold "nowhere" airport with no one there and having a dead battery. 

[Mike Koerner]

Wait. Doesn't the EarthX battery management system also prevent excessive discharge rates? Would that provide protection from a short between the dangling positive lead and the plane's skin?

This leads to another question: How do I handle a dead or dying EarthX battery when I'm on the road?

There are two scenarios I'm worried about. In the first, the battery has reached is useful life and needs replacement, but I don't know it because I live in warm and sunny Southern California. I don't notice the battery's wanning condition until I arrive in Outer-Mongolia (or actually, the next morning when I try to depart) where its cold and now my marginal battery can't cut it. Earth-X (and I love this battery otherwise) says not to jump it. So, do I need to carry the charger and a very long extension cord and hope I can find a friendly native with a place to plug it in? Alternately, I can carry a spare Earth-X battery that is fully charged (they hold their charge for years) and switch the battery out on the flight line. This is an expensive approach to be sure.    

In the second scenario I accidentally leave the master switch ON. This has happened 3 times: twice when I was working on the plane in the hangar (so no real problem, I just recharged the battery with its charger) and once out on the road when I was distracted by a linesman as I was shutting down (there was still sufficient power for a start when I discovered the problem the next morning). In this second scenario, depending on how long the plane is parked, I may have a completely dead battery. Again, it seems like I need to carry a spare battery or a charger.

[Madhatter]

If you always leave the ACL switch on you won't forget the master ( unless you're blind )

[Anticept]

20 hours ago, Mike Koerner said:

Wait. Doesn't the EarthX battery management system also prevent excessive discharge rates? Would that provide protection from a short between the dangling positive lead and the plane's skin?

This leads to another question: How do I handle a dead or dying EarthX battery when I'm on the road?

There are two scenarios I'm worried about. In the first, the battery has reached is useful life and needs replacement, but I don't know it because I live in warm and sunny Southern California. I don't notice the battery's wanning condition until I arrive in Outer-Mongolia (or actually, the next morning when I try to depart) where its cold and now my marginal battery can't cut it. Earth-X (and I love this battery otherwise) says not to jump it. So, do I need to carry the charger and a very long extension cord and hope I can find a friendly native with a place to plug it in? Alternately, I can carry a spare Earth-X battery that is fully charged (they hold their charge for years) and switch the battery out on the flight line. This is an expensive approach to be sure.    

In the second scenario I accidentally leave the master switch ON. This has happened 3 times: twice when I was working on the plane in the hangar (so no real problem, I just recharged the battery with its charger) and once out on the road when I was distracted by a linesman as I was shutting down (there was still sufficient power for a start when I discovered the problem the next morning). In this second scenario, depending on how long the plane is parked, I may have a completely dead battery. Again, it seems like I need to carry a spare battery or a charger.

You starter draws 150-200 amps.

It's not going to tell the difference between a starter discharging, and your airplane burning up. The BMS electronics are there to stop an overheat and maintain cell balance.

On the last point: shutdown checklists!

[airhound]

SLSA’s—Talking about putting an angle on the dangle, you are still playing with fire.  Looking at the affected area, how about, if it has happened several times, then perhaps a Fight Design “Redesign”, retro kit, is needed? Something standard, for the fleet. Something on the order of preventing charger clamps from coming into contact with that lower cowl all metal attachment fitting which would heat up, then cause that localized skin burn. The good news, for whatever reason, the burn died out, rather than grew and  ignited other stuff. Hopefully, the underwriter won’t mind too much getting scalped by a repair station. Maybe get a couple quotes is best in this small market!

[Anticept]

I've passed along recommendations already.

A significant part of the exothermic reaction already takes place during catalyzation of the resin, and they will catch fire in too large of a batch. Once it is cured though, there doesn't seem to be enough energy available to a fire to be self sustaining.

[Mike Koerner]

Cory,

This is a photo I took of a composite sailplane that burned down in a fire in Barstow in July of '87. Lots of planes in the hangar to the right burned up. They thought they had saved this one by pulling it out of the hangar. but it had already caught fire and it continued to burn until all that was left was this cruciform on the concrete.  

 

Remains of glider after fire in Barstow, CA.bmp

[Anticept]

If that was '87 then they were probably made with a vinyl ester. I don't have any experience dealing with that type of resin, but I do know the catalysts are extremely potent oxidizers that can cause violent fires in combination with a fuel source.

The resin used in CTs is specifically what I was talking about, it doesn't seem to want to stay burning very easily.

I might try to light a junk piece with a torch and see if it keeps going. Maybe the paint and fabric slows it down.

[FlyingMonkey]

On 4/16/2022 at 7:33 PM, Madhatter said:

If you always leave the ACL switch on you won't forget the master ( unless you're blind )

That's what I do.  So far so good! 

[sandpiper]

On 4/16/2022 at 4:33 PM, Madhatter said:

If you always leave the ACL switch on you won't forget the master ( unless you're blind )

That's what I have always done.

[EricB]

I get this recommendation and intend to implement it in my CTLS.  Question is, does that not require Experimental rather than S-LSA registration as you are going contrary (or outside of) manufacturer guidance?  Manufacturer was not thinking but FCC says they rule.

 

[Anticept]

Technically approval is required but nobody is going to bust you for putting a fuse in a wire that isn't used for flight operations.

[FlyingMonkey]

I pulled this wire off.  I charge directly on the battery terminals.

[Ken]

Why not just use a wire nut? Easy on easy off?

kEN