Hi Mr. Rawles,
I had a question about the article titled Letter Re: For Want of a Battery. In it you said to connect the Northern Tool & Equipment Solar-Powered Trickle Charger — 5 Watt Item # 339973, with this battery pack . How does the panel connect to the battery pack? And does your recommended Accupower AccuManager 20 Battery Charger (a battery charger for AA, AAA, C, D, and 9 volt rechargeable batteries connect to the 12 volt battery pack via the cigarette lighter plug? Also, could you please tell me how many AA batteries you could charge from one 12 volt battery pack. Thanks for your time and your blog. Signed, – LZ
JWR Replies: Unless it already has one installed, you would have to wire a cigarette lighter-type plug on to the lead wires from the photovoltaic panel. Those are available for any electronics supply store such as Radio Shack. Typically with DC wiring the red or white wire is positive, and that would go to the “tip” terminal on the lighter plug. (Note: Be sure double check the polarity with a volt-ohm meter before plugging it in!) One nice thing about jump packs is that they have a built-in charge controller. If you upgrade to larger capacity storage–such as a standard car battery or better yet a pair of golf cart batteries–either add a charge controller to the circuit or be very careful about checking voltage regularly during charging so that you don’t “cook” your battery.
I own an AccuManager 20 Battery Charger. They were designed by a company in Germany, but I was sad to see that they are now made in mainland China. However, they do work well. They are a “smart” charger– so they will not over-charge your batteries. They come with both a 12 VDC cord (with cigarette lighter plug) and a 120 VAC adapter. The charger has six “channels”, so it can simultaneously hold four AAA, AA, C, D cells, and two 9 VDC batteries.
You can recharge at least 20 AA cells from a jump pack that is fully charged. With a five watt photovoltaic panel it might take two or three days to charge your jump pack. A 10 watt panel (or two 5 watt panels wired parallel) works much better, and a 20 watt panel works even better still. Your ability to “make do” with a smaller panel depends on your budget, how many batteries you need to keep charged, and your time available to re-position the panel to keep it in full sunlight throughout the day.