Solar Shed - An Idea

I have an IDEA😁

I have this nice shed in the back that I use for lumber storage and gardening.  Keeping the door open has been problematic, so I installed a 12 VDC LED light strip I had left over.  I obtained this battery at the electronics flea market, probably should have bought more, they were only a few dollars each.  LiFePo4 batteries are probably the safest Lithium cells in existence (relative statement).  I have used them in a project where the group was motorizing Kayaks.  They were very easy to deal with and very tolerant of the environment and the charging.  

I bought his solar panel at home depot, regular $49.99 on clearance for $13.03.  This is a 7.5W output and 24 volts open circuit.  Max current appears to be 500mA.  

The battery wants about 14.4VDC to charge.  So I went through my parts to see what regulators I might have.  I found an LT1085, one of the first high current 3 terminal regulators.  At 3 AMPS  it should handle what I need.  I built the little perf board you see in the first two pictures with other parts I had.  (220uF caps at 100VDC on the in and out).  

As you draw current out of the solar panel, the voltage drops like a rock.  As the voltage drops below 14.4VDC, the LT1085 just follows the input at about 1.5VDC drop.  Thus when the current draw is the greatest, the voltage drop across the regulator is the lowest.  As the current goes down the input rises, but the power drop across the regulator is also decreasing.  At the end there should be about a 10V drop across the regulator, but only about 50mA trickle charge.  

I prefer not to leave this connected during extended road trips.  But at least I got it going.  I will be interested to see how will the solar panel holds up in the sun, all year.  If the plastic casing does not have UV inhibitors in the plastic, this may be a 12 month solution only.   We shall see.  There is a reason it was $13.03.