Solar Panels for Battery Charging.

[scifi]

With the likelihood of us not flying for the next few months, I was wondering if we should keep our aircraft batteries trickle charged with a small solar panel.

I used to work in a business that had a fleet of vehicles, the more vehicles we had the less each got used, and the more batteries were present. This created an almost constant battery replacement regime. I think the chemistry behind the theory, is that if the voltage falls below 10.5 volts sulphation will occur, which after a few days renders the battery unusable.

The idea of using a small solar panel to supply a constant few milliamps, sound good in theory, but aircraft batteries are generally of low Ah Capacity, so might be overcharged if the panel keeps pushing current into it for weeks or months. Also how would you connect the leads ... The cigarette lighter sockets are usually disconnected with the ignition off.
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[Jan Olieslagers]

If the plane is in a hangar, forget it: you'll never catch sufficient light. If it is not, standing parked will cause much worse worries than the battery discharging, I'm afraid.

The figure of 10.5 V= is extremely optimistic, better keep 12.0 V= as a limit.

OTOH a small panel will never have sufficient muscle to disturn a lead-acid battery, these are quite sturdy things.

And no, I consider it bad design to have the lighter plugs disconnect with the ignition switch - in my self-concocted dashboard there are "before" the ignition switch, though still "behind" the master switch. In fact the "contact" position of my ignition keylock only activates the engine instruments - and, internally, the starter relay.

The issue is quite real, though, my best recommendation is to install a mains-fed trickle charger; these are available for boating (still expensive), mobilhomes and campers (already more affordable) and motorbikes (cheap, if you have a good shop nearby), most of whom know the same issue every year. C-tek is one well-reputed maker.

Still, my own pride and beauty was once parked idle for a full year, yet the battery had enough juice left to start at the first try.

[Lantern10]

Still, my own pride and beauty was once parked idle for a full year, yet the battery had enough juice left to start at the first try.

You Sir were very lucky. I have a 1.5W panel connected to my ride on mower otherwise the hour clock will flatten it in about six weeks.

[Pilot DAR]

I bought a plane which had had a small solar panel installed by STC. I don't get the impression that it worked very well, I removed it before I sold the plane. And certified plane cannot be backward charged through the cigarette lighter socket. The only connection would be to the battery contacts, or its connection to the master solenoid. For those occasions where I will leave one of my planes unflown, particularly during the winter, I remove the battery, and take it inside, occasionally topping it off. I have also found very nice plug in battery tenders. I use them on all of my machines in the winter, if I cannot, or choose to not remove the battery. So far so good...

[Jan Olieslagers]

You Sir were very lucky. Perhaps, yes. It is however also possible that I have a good battery :) For the money it cost, it had better be...

[mikehallam]

Have several solar arrays on the shed/hangar roofs at my strip where no other electricity. Three sets variously continuously connected to a pair of caravans' 12 volt batteries via two regulators. My tractor, my Rans and a pair of older batteries with crocodile clip connection as needed are used ad hoc for drills, soldering, vacuum etc. Every battery has a cheapo regulator in the feed.
Been reliable, don't overcharge and engines start smartly.
The cells were second hand from all the usual sources.
I wouldn't be without them !

[Jan Olieslagers]

PV panels on the roof is a good concept, yes. I have no experience, but isn't it critical to clean them periodically, perhaps once or twce yearly?

[Lantern10]

^ Depending on where you live. A mould will eventually grow on them if not cleaned about once per year. Lived off grid for around 20 years when I first arrived in Australia. Learnt so much a couple of friends and I started a company.

[mikehallam]

Thanks for the cleaning tip. I must be lucky or the British rain does the job ?

They've been up about 8 years without being cleaned. In fact on one set it been up long enough for the home made wooden mounting frame to rot into dust...
I was up a ladder creating a new one only a coupleof weeks ago just before our U.K. "Lock in". The glazed surface happened to still look good.

I should add that the hangars here are not high, so ladder to lean over roof edge is not a big deal..
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[India Four Two]

These days, many gliders have factory-installed solar panels. The DG-1000S that I fly never needs connecting to a battery charger during the summer. The solar panels keep the battery at full charge, which is a good job, because the gear is electrically operated. There is a emergency manual extension but it's a pain to reset it.

[scifi]

Thanks for all the replies so far. I have looked a little more into the electro-chemistry involved, and my original 10.5 voltage would indicate a very bad battery.

There are two voltages worth noting.. 2.04 volts per cell ( 12.24v.) below which sulphation occurs. and 2.35 ( 14.1v.) above which bubbling and gassing occurs, where the water becomes dissociated into two parts Hydrogen and one part Oxygen, ( which is a perfectly explosive mixture.)

As long as your charger keeps the battery between 12.24 and 14.1 volts, I don't think there would be any problems. Overcharging could result in acid fumes being produced, with possible damage to aluminium surfaces, and the need to replace the lost water.

[Deltasierra010]

If you’re not using the aircraft for several months remove the battery, trickle charge it now and again in the workshop. Gliders commonly use Solar panels because they have no charging system, a small panel does not need a charge regulator, but if it’s a turbo with a large battery that needs charging quickly you will need a regulator on the larger panel if you leave it connected for a week.