Sky-tec failure

[Narwhal747]

I don't think I need technical support to do the battery change but I would like to know if/when CC will issue a service bulletin. I'm curious to know what, if any, system changes CC engineering decided were required..

Long story short: CC want's the battery vented

Seem prudent to me (and maybe there is more to it than I'm unaware of). Unfortunately since I also wanted a fuel pod, I could only have one of the two: EarthX or belly pod. CC couldn't vent an EarthX into a fuel pod, which makes sense of course, and there was no easy work-around I guess. Unfortunately I didn't know about all this until the airplane was already built with the fuel pod ordered, so I couldn't get an EarthX battery factory installed. In retrospect I probably would've omitted the fuel pod in favor of the EarthX, but the pod was bit of a panic purchase when I found out I was going to be ferrying the airplane to Alaska myself. I guess there is nothing stopping me from installing an EarthX without venting; not sure how I'd feel about that from a safety standpoint though, especially with it sitting between me and a fair bit of avgas. Ultimately all the options made me airplane pretty porky at 1210 empty (1230 with pod), which I was hoping to offset a bit with an EarthX.

[ptredway]

I think an AFM supplement would be necessary to warn that the main battery cannot be used to run ignition in the same way as the AGM battery after an alternator failure.

Why’s that?

[Andy]

Why’s that?

The ignition system will continue to run with voltages as low as 5.5 V:

"Minimum supply voltage for starting is 6.5 Volts.Minimum operating voltage is 5.5 Volts."

The EarthX battery will completely shut down to protect itself at a much higher voltage than that. When the battery shuts down the engine stops unless you have already select the short duration emergency ignition battery.

If you have an EarthX battery you'd better know what the shutdown voltage is, have suitable voltage alerting, and have emergency ignition on before the battery isolates itself.

[ptredway]

The ignition system will continue to run with voltages as low as 5.5 V:

"Minimum supply voltage for starting is 6.5 Volts.Minimum operating voltage is 5.5 Volts."

The EarthX battery will completely shut down to protect itself at a much higher voltage than that. When the battery shuts down the engine stops unless you have already select the short duration emergency ignition battery.

If you have an EarthX battery you'd better know what the shutdown voltage is, have suitable voltage alerting, and have emergency ignition on before the battery isolates itself.

I think there's a bit more to the story than that. As you mentioned, lithium batteries are different...but many of those differences can be beneficial in an aviation environment.

Regarding you specific point, the EarthX battery management system will disconnect the load below 11.5v. The important part to understand is that the 11.5v occurs much, much later in the discharge cycle as compared to a lead-acid/AGM. A 12v lead-acid battery may get below 11.5v at as little as 10-20% of it's capacity being used whereas that same voltage won't be seen in an EarthX until it's used 95%+ of it's available capacity. Remember, capacity is measured in amp-hours

The most important thing for us as aviators with electronic ignitions is time...

The 900 series EarthX won't reach that shutdown point until some 70+ minutes of operation (the 680 is somewhere between 50 and 60 minutes), granted a few assumptions made on temperature, load, etc. With the EarthX weighing nearly half of the comparable Odyssey, you could install two in parallel and double that runtime.

Now, to your point...in an emergency, voltage monitoring is important. Most of these airplanes I've seen can monitor bus voltage quite well and I suspect a well configured alarm and 11.something volts would be prudent and useful.

Having said all of that, I do think additional steps need to be taken to properly place and vent the battery while also making access to the fault LED in some fashion. Like any other battery, when properly cared for, these things should perform quite well.

[Andy]

The most important thing for us as aviators with electronic ignitions is time...

Sure, but how do you know how much time you have left? We both know that voltage is not a useful indicator of remaining capacity.

What is your strategy for managing main battery, IBBS, and emergency ignition battery in the event of an alternator failure?

[ptredway]

Sure, but how do you know how much time you have left? We both know that voltage is not a useful indicator of remaining capacity.

What is your strategy for managing main battery, IBBS, and emergency ignition battery in the event of an alternator failure?

Batteries can be fickle, largely based upon how they're maintained and cared for. As mentioned, time is what's important and time is most congruent to capacity, all else being equal. Executing a proper load shed procedure, regardless of which battery is installed, is of the utmost importance. This procedure is certainly going to be airplane and conditions specific (redundant attitude, airspeed?, IMC vs. VMC, etc.)

Relative to your question, I would say my personal strategy is twofold:

First, put the airplane on the ground safely and well before we get close to the limits of the batteries. Second, carry more capacity so those limits are farther away in time from the onset of the alternator.

As an example...the J16 battery has a nominal capacity of 12Ah (some documentation says 12.3Ah) or...1 hour drawing 12 amps. At the end of that curve, the battery in nominal condition should be producing 10.5 volts.

The ETX900-VNT at the same 12-amp draw would add ~18 minutes of additional buffer. The ETX680 would be nearly identical to the J16 in capacity/time.

So to bring this full circle, I don't think there's any notable difference in the amount of time one would have flying with a ETX680 vs. a J16...and as such, no need for an update to the airframe manual or PoH. If one was to choose an ETX900 series, you're adding more safety margin to the equation.

[Andy]

....

[KCKS]

I learned a lot about batteries in this discussion so thank you. Back to my original problem, I replaced the starter with another sky-tec and it is starting just like new. I now realize that the starter had been failing for some time, I just didn't recognize the signs. So my starter was definitely bad. 220 hours. As I said earlier, VAF forums have some complaints about the same thing. But it sounds like there are only a couple of us in the FX community that have experienced it.
Blaine

[Lee]

Count me in on this one as well. The FX3 I purchased with 125 hours on it had a failed Sky-Tec starter. Same symptoms as has been described above. Replaced starter...Problem solved. There is a problem with a batch of starters.
I did place the earth X battery (ETX680c) which has been working just fine for the past 100 hours. In response to the concerns about voltage and automatic battery cut off, I placed a pigtail lead from the battery to the front of the pilot seat-easy access. I carry a second small battery kit ( 14,000mAh / 480A powers the jump-starter, air compressor, USB outputs) that plugs directly into the pig tails should I ever need a jump start or additional ignition power. The small air compressor just a bonus. Ya, its about 4.5 lbs but with the 10 lbs wt reduction removing the Odyssey I'm still lighter. The back up kit sits under the back seat just fine. The kit I have: https://lionenergy.com/products/lion-cub-jc

[Andy]

Count me in on this one as well. The FX3 I purchased with 125 hours on it had a failed Sky-Tec starter. Same symptoms as has been described above. Replaced starter...Problem solved. There is a problem with a batch of starters.

Has anyone identified the specific starter defect that is causing problems?