Solar Battery Charging / Maintaining in the Tie-Downs

[GraemeSmith]

Fly a few patterns to finish the day with the electronic ignition sucking down the amps and the alternator not keeping up. Even if I smartly turn off the electronic ignition as I clear the hold short and turn it on again for the next pattern - with most of the pattern being a glide - 3 patterns and the battery is depleted for next flight..... No electricity out in the tie downs.

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A solution - a solar panel on my tie down box, pitched just enough to let the rain run off and slightly favor the sun. But NOT pitched that it will blow over in our windy tie downs. This is a nominal 100w panel with an open voltage around 28v and under load of an appropriate controller can be set to 24v or 12v for charging.

Since testing the panel has been mounted and the connectors secured to the mount.

The solar panel plugs to the controller (weighs 8 oz so it is installed on my battery box).

The controller senses battery voltage and when the battery drops in voltage - applies solar panel input to the battery to charge it. When the battery is charged it disconnects the solar panel. And when the battery loses a little charge - it charges it up again. On this controller - excess power is made available on another set of leads to power any load you might apply to it. I'm planning on wiring a circuit to the panel to charge cell phone / iPad for when the master is off and the solar panel is plugged in.

In practice I went with a 100w panel that appears to manage to produce about 50w at 12v (nominal) on even a cloudy day in the tie downs. Sun comes out and it easily delivers 100w lying flat.

There are a range of controllers available, some can be programmed in quite sophisticated ways and include temperature compensation probes. In practice this controller is a bit simpler - you connect it to the battery - if senses which type of battery you have connected and adjusts its charge profile to match and then you apply the solar charger and it delivers available current as needed.

The other thing to watch for is IP rating - which is a weathertightness / waterproofness of the panel/controller and interface/connections. Higher numbers are better.

If you leave the controller installed - without a solar panel attached is does use <0.05amps as it monitors the battery. I think I will just carry along a small 10w panel which weighs less than 1lb for when stopped for any length of time when I fly out.

The second set of SAE connectors below the solar plug in is for a regular battery charger. Battery charge must not be connected to the solar controller.

The Aluminum bar extends the connectors to a flush port in the side of the cowl.

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Amazon prices:

Panel $92
Controller $18
Low loss 25ft extension cord $30

About 2 hours to put it together.

[Rynoth]

Thanks for posting this... I'm still in Phase 1 with my Aerovee Turbo but with the draw of the post-shutdown cooling system in the back of my mind I've always been wondering how I can keep the battery topped off on cross countries. A small lightweight solar panel plugged into my hot 12V socket just might be the ticket.

[lakespookie]

Whats the total weight of the system? call me crazy but the experimental part of my brain says it should not be to hard to install this in the airframe if the weight is reasonable using a flexible panel.

[Matt541]

Wow! Thanks for posting this Graeme.

Not bad price wise either, and with the cost of solar continuing to decrease, it'll get better. Now if only other aviation aspects would too.

[GraemeSmith]

Whats the total weight of the system? call me crazy but the experimental part of my brain says it should not be to hard to install this in the airframe if the weight is reasonable using a flexible panel.

Way ahead of you there! I'm running numbers on some different panel types that might suit and will report.

[GraemeSmith]

Just to follow up.

12 days in the tie downs with no flying. Mainly stormy gray weather. When plane was put away - battery voltage was 12.2v. Today - went to start it - 13.4v. Engine spun up like a top! I'll take that as a win!

Here is the tidied up flight box:

[Bryan Cotton]

Cool. Now you just need to add the windmill attachment and all the bases will be covered.

[jrs]

I have a battery powered trolling motor that I leave in the water where there is no electric source. Bought a 10 watt charger from Amazon and put it on a post. Simply hook it to the battery when I dock the boat. I believe that it was 28" x 14" and it has the regulator built in. Has been working great for a couple of years. They make 5, 10, 15 watt versions and the 10 will keep the battery charged even if I am using it a few hours a day.

https://www.amazon.com/gp/product/B004Q ... UTF8&psc=1