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How to Get Light From Your Backup Battery

By Patrick Nelson
Apr 4, 2013 5:00 AM PT

Over the last few months, we've been building out a solar generator. The project started as a simple, heavy-duty battery with a cigarette lighter adapter -- inspired in part by images of Hurricane Sandy victims scrambling to find methods for charging devices like smartphones and tablets.

How to Get Light From Your Backup Battery

Deep Cycle Battery
Optima 8014-045-FFP YellowTop Group 34/78 Deep Cycle Battery

We then added a photovoltaic solar panel with charge controller to the project to extend battery life. The panel collects energy from the sun's rays and tops up the battery, providing theoretically endless power for charging phones.

Let There Be Light

The third part of our project is to add light. New, super-efficient Light Emitting Diode, or LED, technology means it's possible to create bright light with very little electrical draw.

This technology is a perfect solution in the event of an extended power outage -- or a camping trip.

Step 1: Source Your Lights

Look for LED technology designed by leader Cree, and made or licensed by the company. I've written about ipso-facto-standard Cree before in High-Tech Flashlights Could Turn You Into a Collector.

LED Off Road Light
AGT LED Off Road Light

Look for a low amperage draw -- a couple of amps is perfect. Take advantage of vehicle applications, which are already in 12-volts DC, the correct voltage, rather than patio flood lights -- an alternative -- which need converting.

I used an off-road work light designed for All Terrain Vehicles made by AGT (about US$62 for a pair at Amazon). Each light uses nine 3-watt Cree chips creating a bright 1200 lumens each.

Importantly, one light draws an incredibly low two-amps. So, if you're using the 55-amp hour Optima battery suggested in the first part of this How To series, one AGT light will run for 13.75 hours before the battery becomes 50 percent depleted and will need a sunlight shot from the solar panel and charge controller combo.

Step 2: Mounting

Mount a light-included stainless steel bracket onto a polyethylene battery box by drilling an appropriate hole in the box lid and fastening with light-included bolt. You can pick up a battery box, sometimes called storage case, at auto parts sellers.

Battery Storage Case
Mr. Gasket Battery Storage Case

The boxes are also often used in trolling applications for fishing, so marinas are a good source too.

Then attach one of the lights to the bracket. Keep the other light as a spare.

Step 3: Prepping the Charge Controller

Remove the existing fuse from the existing red wire that runs between the charge controller terminal labeled "Battery +" (or similar) and the battery.

Remove the existing cigarette lighter adapter from the terminals labeled "Load +" and "Load --" on the charge controller, and put the adapter to one side.

In-line Fuse Holder
In-line Fuse Holder

Step 4: Gather the Parts

Obtain an in-line automotive pigtailed fuse holder, a 10-amp fuse, some butt connectors and ring terminals. Fry's Electronics is a good source of parts.

Tip: You can read about wire and the tools to use in Coming to Grips with Wire.

Step 5: Crimping Connections

Crimp one red ring terminal onto the included black lead that's connected to the LED light's housing. This is the negative side.

Crimp one end of the new empty fuse holder's red pigtail to the included red lead that is also connected to the LED light's housing. Use a blue butt connector. Then crimp a red ring terminal to the other end of the fuse holder's red pigtail. This creates in in-line fuse in the red, positive side of the light. Don't add the fuse yet.

Step 6: Wiring

Attach the red wire that leads from the LED light, via the fuse holder, to the positive terminal labeled "Load +" or similar on the existing charge controller.

Connect the black wire to the negative terminal labeled "Load --" on the charge controller.

Step 7: Turn on the Light

Insert the load circuit fuse and then the battery circuit fuse. The light will illuminate.

Morningstar SunSaver Charge Controller
Morningstar SunSaver Charge Controller
Tip: Morningstar SunSaver charge controllers like the one used in our project will switch the light off automatically when the battery capacity drops to a factory-set level of depletion. This is designed to avoid battery damage. Or, turn off the light by carefully removing the black wire from the negative Load terminal on the charge controller.

Want to Ask a Tech Question?

Is there a piece of tech you'd like to know how to operate properly? Is there a gadget that's got you confounded? Please send your tech questions to me, and I'll try to answer as many as possible in this column.

And use the Talkback feature below to add your comments!

Patrick Nelson has been a professional writer since 1992. He was editor and publisher of the music industry trade publication Producer Report and has written for a number of technology blogs. Nelson studied design at Hornsey Art School and wrote the cult-classic novel Sprawlism. His introduction to technology was as a nomadic talent scout in the eighties, where regular scrabbling around under hotel room beds was necessary to connect modems with alligator clips to hotel telephone wiring to get a fax out. He tasted down and dirty technology, and never looked back.

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