MOD Carbon Cub Solar Fuel Tank Covers?

[ve6yeq]

As I generally do not have the opportunity to hangar my Carbon Cub FX-3/EX-3, it is tied down outside with covers from Bruce's Custom Covers (Extended Canopy Cover, Cowling Cover, and Tire Covers). Although I have a Lithium-based EarthX ETX-900 main battery, which has minimal self-discharge and does not require float charging, the Lead-based PowerSonic AGM Ignition backup battery is designed for continuous float charging and requires more than 24 hours of charging to reach full capacity. Since I only fly for less than a couple of hours a week on average, the ignition backup battery never gets fully charged. To keep everything in top condition, I am thinking of getting a small portable solar panel, and charger.

Initially, I was thinking of just an external solar panel I could attach to the horizontal stabilizer when it was tied down, but then I remembered Mike Patey's videos on his "Scrappy" build, where he integrated flexible solar cells into the metal top surface of the wings. Although the Carbon Cub has mostly fabric wings, the metal wing fuel tank covers still offer a possible mounting location. Has anyone attempted this?

 

[ve6yeq]

Here is Mike Patey's video on how he integrated solar panels into the metal wing skins:

 

[Neal]

An external solar panel would work fine I'd think but my concern is it getting blown into something causing damage to you or someone else's plane.

You could possibly find one that fits in the clear glass area over the cockpit but you mention using a cover so that's out.

I think I'd consider an external panel payment placed on top of your Bruce's cover on the aft top and strapped on securely?

Or do nothing and with your knowledge of the system you should be fine.

I'm not a fan of putting something on the wing and causing some cosmetic damage for little gain.

 

[Cactus Charlie]

the Lead-based PowerSonic AGM Ignition backup battery is designed for continuous float charging and requires more than 24 hours of charging to reach full capacity.

I relied on 12 V AGM SLA batteries for about 30 years of sailplane racing. After each contest flight they were put on the charger in the evening and were fully charged the next morning.

My ignition battery current and voltage data seem to show that the 2 AH AGM in my FX-3 is fully charged soon after engine start. I also have current and voltage data for in flight intentional discharge tests that show rapid recovery to full charge.

What is the source of your claim they take over 24 hours to charge and what method was used for charging?

 

[ve6yeq]

The idea of mounting a panel to the top of the Bruce's extended canopy cover might work and be very simple. If you take a flexible panel such as a BougeRV Arch Pro 100W N-Type TOPCon Flexible Solar Panel, which has mounting holes, and attach some small bungee cords with small hooks to the top of the cover.

The electrical changes to enable float charging for both the main battery and the ignition backup battery are simple: move the ignition battery breaker from the main bus to a direct connection to the main battery. The solar charger can then be connected directly to the main battery.

 

[Neal]

You could also just lean the seat forward and direct connect to the battery. Alligator clip type things.

 

[ve6yeq]

I relied on 12 V AGM SLA batteries for about 30 years of sailplane racing. After each contest flight they were put on the charger in the evening and were fully charged the next morning.

Not all AGM batteries are built the same. Some are designed for deep-cycle use, such as your sailplane, and some are for float use and are damaged by deep discharging (e.g., emergency backups for main powered fire alarms). The PowerSonic PS-1221 is not a deep-cycle battery; it is a "general purpose" design, according to the datasheet.

My ignition battery current and voltage data seem to show that the 2 AH AGM in my FX-3 is fully charged soon after engine start. I also have current and voltage data for in flight intentional discharge tests that show rapid recovery to full charge.

The open circuit voltage climbs quickly, but a discharge test, such as running the right ignition from the battery during the run-up until the voltage stabilizes, shows a much lower voltage if I have not flown the plane recently, and after flying a lot.

Before leaving CYTZ (no flights in the last week and after an extended engine warmup due to airport congestion):

And after flying a lot (about 15 hours in the previous 48 hours):

What is the source of your claim they take over 24 hours to charge and what method was used for charging?

Figure 14, from the PowerSonic Technical Manual for Sealed Lead-Acid Batteries shows a typical charging performance for a changing voltage of 14.1 Vdc (close to the 14.0 Vdc that I observe).

(The only logical units for the x-axis is in hours as a 100% discharge must charge at 0.1C for a minimum of 10 hours if the battery were ideal)

 

[ve6yeq]

You could also just lean the seat forward and direct connect to the battery. Alligator clip type things.

No need - I have a battery charging pigtail that I use for the AC charger that I can also just connect a solar charger to.

 

[Cactus Charlie]

Not all AGM batteries are built the same. Some are designed for deep-cycle use, such as your sailplane,

I never used deep cycle batteries. I used a lot of different types over the years but they were all similar general purpose batteries and often advertised as suitable for alarm systems.

I retired from sailplane racing a while ago but I still have the last pair I used. They are UB1280 (12 V, 8 AH).

 

[Cactus Charlie]

I too had studied the PowerSonic Technical Manual and it is the reason I abandoned in flight discharge testing to confirm ignition battery capacity.

The aircraft charging circuit provides no current limiting and the charge current after a 30 minute discharge test was well over the maximum allowed charge current.

I expect I have the only FX-3 with ignition battery current monitoring. In the normal emergency ignition test the current is about -1.1 A. When the test terminates the battery charges for a few seconds at 0.8 A then quickly settles to 0.1 A to 0.2 A for the rest of the flight.

If the battery draws 0.1 A at 14.1 V I think it is charged.

 

[ve6yeq]

Updates on the solar project: The solar panels, solar charge controller, and some cabling have arrived, and more things are on the way. The system is looking like the following so far:

The only bit to finalize is the connection to the master contactor under the pilot's seat.

I am using the BougeRV Arch Pro 100W Flexible Solar Panel because it fits between the lifting rings on the cub, appears reasonably lightweight and robust, and includes mounting grommets for attaching to the cabin cover. I have the option to use two panels when charging an accessory battery for tasks such as Starlink Mini use on the ground.

I selected the SmartSolar MPPT 75/15 as a high-quality, high-efficiency lithium battery charge controller. This is connected to the solar panels via a 10 ft 12 AWG MC4 cable (with optional MC4 T connectors for 2 parallel panels).

As the panels, charger, and cables are not particularly lightweight, I have decided not to mount them directly to the plane; instead, I will leave them removable. To connect it to the main starter battery, I cannot use the existing Optimate charger pigtail, as it is limited to 13 A, and with 2 panels, the solar charger will be generating 15 A. As the Anderson PowerPole PP15-PP45 connector system has a round panel mount option that can replace the cigarette connector on the back of the seat base, I have ordered a 12 AWG 1 ft patch cable from the charger to the panel and a 1ft 10 AWG with 40 A fuse cable for the panel to the master contactor. I also got an SAE-to-PowerPole patch cable for connecting my current Optimate AC charger. While I am at it, I will add two main battery connectors so I can use the second connector to connect an accessory battery (via a DC-DC charger with boost) in the future.

I have not yet opened up the access panel on the belly to count how many things are currently connected to the battery side bolt of the master contactor, but I have a feeling that there might already be more than the recommended 3 rings, so I might need to add a small bus bar to connect all the "always on" loads.

 

[ve6yeq]

I too had studied the PowerSonic Technical Manual and it is the reason I abandoned in flight discharge testing to confirm ignition battery capacity.

The aircraft charging circuit provides no current limiting and the charge current after a 30 minute discharge test was well over the maximum allowed charge current.

The lack of a proper battery charger may be one of the factors contributing to the short lifespan of the PowerSonic batteries we are seeing. The charge algorithm used by the solar charge controller I have goes to great lengths to avoid undercharging or overcharging Pb-based batteries, including Bulk, Absorption, Float, Equalization, Temperature Compensation, and memory between power cycles, so the battery is not recharged if it has not been discharged enough.

I agree that an in-flight battery capacity check via deep discharge is not advisable without a real charge controller, not just the current simple diode voltage drop.