I've been into lighting lately. I've compared popular lanterns recently, tried my hand at a Crisco candle (and again here) but one thing I haven't figured out was how to provide expedient long term lighting that could work with my small solar setup. In fact, when I originally attempted my solar setup, I bought two 8-Ah (amp-hour) batteries but later decided that they were simply too small for running a laptop, our portable DVD player, and so on. But then I had an idea when I was going through some of our camping supplies and came across an extra LED camping light.
The setup was about as simple as it can get (pictured right). I clipped off the plug end of the camp light, split the positive and negative wires to give me something to work with, and attached two female (spade?) connectors to the wires. I used these connectors because the small 8-Ah battery that I wanted to use had male ends. I should point out that you do need to know which wire is positive and which one is negative. I guessed (sort of) and got it right but I decided to test the setup with the wires on opposite terminals and the light didn't work, so that confirmed I was right. It's probably best NOT to do that but I honestly didn't know how else to be sure!
Anyway, I then decided to try it out and left the light on for a little over four hours. After taking some voltage readings (using a basic multimeter) and then doing some research I realized that I had discharged the battery WAY too far! Oops. Here's what I found:
- All 12-volt batteries should read right around 12.7 volts when fully charged. When I measured my battery I found it to read about 12.75-12.8 volts (depending on at what time after charging that I measured it) which is a little higher than the expected 12.7 volts; this is likely due to me not letting the battery set long enough for everything to "settle down" because I had just finished topping the battery off using my trickle charger.
- I then let the light stay on for slightly over four hours. Learning my lesson, I waited several minutes before taking any readings and found the voltage to read right around 11.7 volts. After consulting this deep cycle battery FAQ (and referencing a table in the State of Charge section just below in the link) I found that I had actually discharged my little 8-Ah battery to less than 30% charge... yikes! Nearly everyone says never to go below 50% charge. I went way past that and didn't look back.
- Only after I realized this did I choose to do more research--that I should have done beforehand--on the LED light I was powering and found it to be a 15-watt bulb. The math says that a 15-watt bulb uses 1.25 amps at 12 volts (where volts x amps = watts). Now, multiplying 1.25 amps by 4 hours means I used at least 5 amps of current out of my 8-Ah battery, which is obviously less than the 50% thresheold. While it doesn't quite line up with the table mentioned, it is fairly close and I did run the light longer than an 4 hours I used in to do the math above.
I was actually very impressed with the setup. Here's a comparison of what a bedroom looks like with this setup and others (click images to enlarge):
In my opinion, it's hard to tell a difference between my camp light and lantern. Since I happen to have a second 8-Ah battery and another camp light (it's a bit different in design) then I could essentially provide descent light in more than one room. The only major problem I would have is needing to rely on my solar panel and enough sunlight to properly recharge my batteries each day. Certainly, this is not going to happen but even if I could get proper sunlight half of the time then I have effectively doubled my other lighting options. That's worth it to me.