DIY: Solar Powered Battery Rechargers

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How to Check Your Batteries

LET THE SUN JUICE YOUR BATTERY HABIT

Thirty years ago, the concept of energy from the sun was as radical as a Jimi Hendrix solo. But then, things we never dreamed of--like notebook PCs, CD players, shirt pocket cellphones, and 18" satellite dishes--are as commonplace today as Chinese shoes. So whatever happened to solar power? It may not have progressed as some technologists had hoped in the '70s, but it's still become a viable alternative for situations where no other power source is available (and as a toy for the Sharper Image set). But the lack of significant improvements in lead-acid storage batteries, and the continued high cost of solar photovoltaic manufacturing, continues to make this technology a costly one. There's one place where solar power is not only useful but affordable. We'll get to that in a minute.

Your So-Called Life: Batteries Not Included

Looking around your home, you'll likely find dozens of small gadgets that run on the ubiquitous AA battery. Virtually every remote control, portable radio, tape player, and wall clock uses this type of battery as a power source. And, if you're like me, you've bought and thrown away these batteries by the fistful over the years. If you multiply that by 300 million other power-hungry Americans, you can appreciate the eventual ecological impact of this small consumer item. So, the first thing you can do to ease up on the environment a little is to use rechargeable Nickel Cadmium (NiCd) type batteries. While these batteries cost three or four that of "disposable" alkalines, they can be used dozens of times before depleting their recharge capacity.

AC rechargers for NiCd batteries are readily available and inexpensive. Radio Shack has an entire page in their catalog which features no fewer than nine rechargers, ranging from one which charges 2 AAs overnight by plugging directly into a wall socket (RS#23-133 $7), to one which charges up to six D, C, 9 volt, AA, and AAA batteries in just five hours (RS#23-233 $28). The Seventh Generation catalog sells Saitek's revolutionary new digital recharger that can even recharge regular disposable alkaline and carbon zinc batteries. A microprocessor in the Eco-Charger (Cat. #17-0013, $54) analyzes the batteries you put into it and can tell you how much charge is left, what the recharge time will be, and if the battery is totally spent. It can accept 4 D, C, A or AA cells. Seventh Generation also sells a very useful organizer called The Battery Rack (Cat. #06-0171, $15). It has compartments for charged cells and cells needing charging for AA, AAA, C, D, and 9v batteries. The unit holds up to 40 batteries and comes with a built-in LED battery tester.

The Saitek Eco-Charger

How cost effective is using rechargeable batteries? The Radio Shack catalog quotes an independent study that claims "...using alkaline batteries in a headset radio operated two hours a day for three years is about $633. The cost of using NiCds instead-including the cost of the recharger and electricity-would be about $26..."

Going Solar

So, why not use solar power to recharge your batteries? Unfortunately, Radio Shack doesn't offer any such products, but Edmund Scientific does. In their latest catalog, several solar battery chargers are offered but one is particularly useful. The small Multi-volt Output Solar Panel (Cat. #U39,806) has a built-in compartment to charge 2 AA batteries but also features a switchable power output (9, 6, 4.5 and 3 volts), a six foot cord with five male plugs to fit many small radios and tape players, and a set of alligator clips to power items not fitted with an external power jack. At $22 (plus shipping and handling) this recharger not only tops off your NiCds but can be used to do some fun solar power experimentation with solid state devices. It weighs just five ounces and measures 3.5" x 6.5" with handle/angle adjuster folded.

Knowing that you're likely to throw away the box it came in, the manufacturers have thoughtfully put all the instructions on a label glued to the back of the panel of the unit itself. On it there's also a chart showing the equivalent voltage of typical devices and how they match up. For instance, a device requiring 3 AA batteries needs 4.5 volts and typically uses 100 mA. To power such a device, simply find the appropriate plug from the plug assortment and switch the panel's output to the 4.5 volt position. If there is no external power jack, you open the battery compartment of the device and clip the red alligator clip to the positive terminal and the black clip to the negative terminal inside. Make sure you have the polarity correct before applying power.

To use the solar charger, you slip two discharged NiCds into the compartment, set the slide switch to "recharge" and set it in a south-facing window. In the evening, you set the recharger under a lamp. Do this for two days and your batteries are ready to go. Even on a cloudy day, there'll be enough voltage generated to trickle-charge batteries. Placing the recharger under a lamp allows you to use waste power from the lamp to recharge your batteries.

I've used this recharger for two years now and have saved more than twice the cost of it in AA batteries alone. I also use it to recharge the battery pack in my 2 meter amateur radio transceiver and go for weeks listening and talking on solar power! This is a very cheap and fun introduction to solar energy and it works.

KISS's Mercury II Solar Power System

The Edmund Scientific Company catalog has several pages devoted to solar power products including high output solar cells which can be connected in series or parallel to get higher voltages or current. One ready-made solar power pack (Cat. #U36,083) looks like an good option for taking a portable, rechargeable power supply into the wilderness. The power output can be switched for 6 or 12 volts providing up to 30 watts of power at 5 amps. A larger version (Cat. #U37,343) provides up to 96 watts at 16 amps. But, to accomplish this feat, the price is $260 for the smaller unit and $495 for the larger. Keep It Simple Systems (KISS) sells a whole line of solar systems for juicing the batteries in your laptops and PDAs. They claim their Mercury II system ($400) powered a PB 1400 for eight hours and still had 96% of its charge left. The Mercury II is compatible with over 300 laptops. KISS's latest product is the PowerCover ($200), a battery charger that slips into the BookCover slot on a PowerBook 100. It weighs only a pound and comes with a 10' cord so you can keep your PB in the shade while the PowerCover takes a sunbath. [Editor's Note: We have not had a chance to test the KISS products yet, but hope to do so in the near future.]

Those wishing to get "off the grid" completely, or looking to supplement their home electrical supply by adding solar power to handle serious electrical needs such as water pumps, computers, entertainment systems, lights, etc., will need the help of some folks who've been doing just that for years. Steve and Liz Willey of Backwoods Solar in Sandpoint, Idaho are true pioneers in the field, living in the solar powered future, designing and selling full-blown solar powered electric power plants for modern homes. Their catalog of solar power equipment includes everything from solar collectors and power inverters (to change solar DC to AC used by many household appliances), to gas powered refrigerators and low voltage water pumps. You'll be amazed at how much you can learn about solar power just by reading their catalog!

- Ken Reitz [3/23/98]

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