Litium battery question

[Eric Page]

Note that the ETX680 and ETX900 share the same case size: "E". Either will fit in the same battery tray. If you have an electrically dependent engine and a single battery, you might consider using the 15.6Ah ETX900 instead of the 12.4Ah ETX680. Doing so will achieve longer alternator-out endurance, or the same endurance with less load shedding required. Weight difference is 0.8 lb.

Even without an electrically dependent engine, there are advantages to using the ETX900. It can supply higher starting current and tolerate higher recharge current. Those things, combined with its higher initial capacity mean it will likely last longer in the same environment than an ETX680.

Whether the longer lifespan will favorably amortize the $70 higher price is an open question...

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Edited to add:

If you have a 912iS (and presumably a 915iS), neither of these batteries meet the minimum battery ampere-hour capacity listed in the Rotax installation manual, but the ETX900 is nearly big enough.

ATTENTION
The use of rechargeable batteries with lithium–ion technology should only be
used in combination with a suitable battery management system. If such an battery
is used, the responsibility is up to the aircraft manufacturer. The approval of
the relevant aeronautical authority may be necessary. For installation of lithium ion
batteries refer e.g. to FAA AC No: 20-184

ATTENTION
Observe the specifications of the battery.
The size of the battery needs to be adequate for essential flight equipment and has to
meet the airworthiness requirements of its place of operation.
When sizing the battery ensure that during each operating state and also during the transition
between two operation states a sufficient supply of the display is guaranteed (e. g.
during engine start). Furthermore, it must be ensured that at least 30 minutes after failure
of the primary power supply the display is supplied with sufficient energy, if it is necessary
for a safe operation of the aircraft.

Nominal voltage: 12 V
Internal resistance: maximal 10mΩ at -18 °C (-0.4 °F)
Cold Cranking Ampere (cca): At least 350 A at -18 °C (-0.4 °F) (SAE J537)
Capacity: At least 16 Ah

[FlyinFish N928M]

Hello guys, You are touching on a situation that is worth exploring. I have been test running my 912ULS, B&C AVC1 regulator with an Earth X 680, and my G3X is indicting after start up 13.4 volts with a high amperage. Examples are 3400 rpms at 13.5 Volts at 15amps, or 4000 rpms at 13.8 V at 18 amps. Called and talked to Earth X, they said this was normal with an avionics load at 6-7 amps, and roughly 11 amps leftover to charge the lithium battery. Only once did my system normalize to 14.4 volts at 6 and 7 amps. This did occur at the end of one of my run sessions, however I have yet to repeat this condition. Being that I'm on the ground testing while using my header tank as a main fuel tank, I run out of gas after about 20 mins. Thinking if I run longer than 20 mins my battery will normalize. As mentioned from Earth X, lithium batteries have a very low charge resistance, therefore they command as much amperage as they can get until the battery is back to full charge. Once charged the amps should come down, and voltage should go up. Again, Earth X tells me what I am experiencing is normal.

The million dollar question is, does anyone know the max continuous time for AC generator at full capacity? My fear is that this situation may over heat, or overtax my copper windings around the magnets and cause a total failure. On take off, I will be running at max power, then to 5500 rpms for an extended time. Should I be concerned? I do not know enough about the rotax electrical system or Earth X batteries to know any better.

Any other thoughts from other Rotax 912 pilots using the AVC1 and Earth X Battery?

Thank you for your comments!

Mike

[fastfred]

I have run both types and mostly the Lithium for the past few years. areovoltz is the one kitfox put in mine I think. It works fine if you don't run it down too far . They do have their own charger that is complicated to use. I also use a lithium maintainer / charger than works fine also. the answer to your question is no you do not need to keep a charger on it when there is no load.

On my Remos I recently traded the odyssey for An Antigravity lithium battery with more power and saved 12 lbs. They are much less than the earthx and it fit in my existing box. Google them.

[PapuaPilot]

I would never do this intentionally and haven't done it accidentally. I would use the formula to see what it theoretically could do.

I estimate I can go approximately 2 hours on the EarthX 680 battery after loosing my charging system running one G3X 10" screen, com radio, transponder and a few other circuits. Lights and trim are part of my essential bus, but are intermittent loads aren't included, but are available. I bypassed my master solenoid, so the coil is not part of the load. I believe my load is between 5-6 amps when I go to my essential bus.

[Backpacker]

I’m still building but purchased a Earth X and it has sat in the shipping box for a year aprox and the other day I checked it and was 13.1 V. Then I charged it with a Lithium Optimate charger which took aprox 45 min and then was at 13.6 V right after charging.

[Slyfox]

I just went through changing to the earthX. I put in the 680C. I have the 912uls engine. I also put in the B and C regulator, very nice unit. I made sure it was charging like 14.3 volts. I also got the led light for the panel, something that earthX sells to tell you if you have a problem. I don't put it on a charger and it cranks very fast no matter what the temp outside is. plane starts right up. I like it.