A few months ago I put together a basic backup power system (read about it here) that included a deep cycle battery, power inverter, solar panel, and everything to easily connect it together (pictured to the left excluding solar panel). At the time I did very little testing, trusting that what I had done would work. Well, a few nights I had a real world opportunity to test it out because of a two hour power outage… the result was a success. I was able to use my laptop (no internet though) and charge my cell phone over the course of an hour of use without any trouble.
In fact, the results were better than expected in large part because I hadn’t bothered to keep the charge topped off for about a month (which is a huge no-no by the way). Anyway, I took a voltage measurement of the deep cycle battery before using it and found the voltage was approx. 12.8 volts (still roughly fully charged) and after a full hour of use the voltage dropped to around 12.5 volts. From what I gathered in the past, the voltage will read about 12.2 volts at 50% capacity, which is the lowest you want to discharge a deep cycle battery. [Note: a fully discharged battery will read 10.5 volts or less.] In this case, the battery had about 75% capacity when I finished using it.
So, I figure I could have used my laptop for another hour or so without much problem. This particular laptop is old and a bit of a batter hog, so I figure that if I’m just using my power system setup to run a small 12 volt dvd system or charge a cell phone or iPod then the battery life should be much better… I think.
I should point out that I was losing some efficiency because I was converting the original DC power into AC power and back into DC power because of the inverter. In order to reduce such inefficiencies I should attempt to eliminate the power inverter where possible. That is, connect a DC device directly to the DC battery.
Also, I made no attempt to charge the battery via the solar panel setup. I figure that will have to be an experiment for another day. By and large it was a success; although, I’m still not sure it was worth the money.