A Solar Box
After working with the box for a while I identified features to add to the box. I'll discuss these as well as the practical performance of the box.
First I wanted something to indicate how much sun was getting to the box. If I set the box outside on a sunny day it gets the best light. If I set it in the car during the day like I have normally done it gets somewhat less light. It also gets a bit less light in the back yard because it is really in the subtle shadows of small branches at the top of trees. In these cases it is hard to tell how much less sunlight gets to the box. This is because the eye is good at compensating for light levels. A cloudy day might appear to be half as bright as a sunny day but in reality it is maybe 1/10th as bright. The indicator is an ammeter that has been shunted to indicate full deflection at high noon on the brightest day in June.
I also wanted to indicate the state of charge. For a sealed AGM battery the most accurate way available is to use a digital volt meter. I got a so called 2 wire digital voltmeter that is powered by the source it is measuring. Since it draws power I wanted it running only when I needed to measure the voltage. I rigged a push button switch that is closed only when it is pushed down.
I also added a BNC connector for a light stalk. This is a light stalk that is typically used for DJ stations and synthesizers. It runs on 12v so it works here without any special provisions.
I also built a new higher quality enclosure to mount these components.
Pictured here is the box with the new features added. I keep a 12v cell phone car charger and a NIMH battery charger.
I have kept the cell phone charged exclusively with this box. I have also kept my NIMH AAA and AA batteries charged exclusively with the box. This works as long as it gets some good sunlight during the day.
There have been some periods of cloudiness lasting up to a week.
In conclusion this has turned out to be a viable off grid means of providing small amounts of electricity for various electronic devices. Later on I'll extend it or build a larger box with higher capacity.