Thursday, July 10, 2014

DC Lighting

Once the sun goes down, things change. Our world seems to get smaller because we can't see very far by the light of the moon and stars. Things that we would step around in the daylight tend to jump out and attack our ankles, and unexpected noises can cause fear and unease.

For centuries, people understood that once the sun set the day was over and it was time to retire to the comfort and safety of home. Agricultural societies set the pace of their daily life on the rising and setting of the sun, and most people were content to sleep when it was dark out and work when it was light. Oil lamps and candles provided light for the times you needed to be out and about after dark, and lit the homes of people who needed to stay up. The trusty campfire provided a comfortable way to beat the chill of evening and gave us a place to relax and tell stories.

Then came electricity 

The first battery was invented in 1800; the first electric motor in 1821; Edison founded Edison Electric Light Co. in 1878 and introduced his incandescent bulb a year later. Vacuum tubes (precursors to the transistor) came about in 1904, electric refrigeration in 1913, and the transistor in 1947. Since 1950 we have accelerated our use of electricity with phones, computers, and televisions to the point where they are more a part of our lives than the sun rising and setting. In the last 200 years, people have forgotten how to live by the cycle of the sun. There is no longer much difference between night and day because we can always flip a switch and have light when and where we want it.

In the event of a disaster where the normal supply of electricity is interrupted, knowing how to replace small parts of what we're used to can have great psychological and morale-boosting effect. Having a night light for a frightened child (or adult) can make a world of difference in their newly disrupted lives, and being able to charge a cell phone, iPod, or radio can bring a semblance or normalcy to a chaotic time.

The options for backup lighting are numerous

Everyone should have flashlights (plural) as part of their kit, but what do you do when the batteries wear out? One option is to buy in bulk - always look for the big packs of disposable batteries so you can change them out when needed. The better option is to buy rechargeable batteries (Li-ion, NMH, NiCad, etc.) and have a way to recharge them that doesn't require a wall outlet. My personal preference is for solar battery chargers like those found here. In a pinch, those stupid little solar sidewalk markers (like these) usually have a single Li-ion cell (AA or AAA sized) in them and the solar panel to charge it.

Sidewalk lights can also be used for indoor illumination (a basis for a future article) if you remember to put them back out in the sun during the day  - a good "chore" to assign to children. Since they consist of a solar cell, a battery , and an LED, they are pretty self-contained and provide light for roughly 8 hours when new. They'll probably also be a resource you may be able to scavenge after a disaster. If you're out looking for things, keep an eye open for anything with a solar panel - it will likely have a battery somewhere in the circuit.

Improvised lighting

OK, you've weathered the worst of the storm and now you're in the process of rebuilding or gathering your things so you can move. If you have a shelter of any kind, light can make it more of a home rather than a hovel. Now I get to tie together some of what I wrote about in my last two articles.

In order to have light you're going to need a few things.
  • A source of electricity. Usually a battery of some sort, or a battery hooked up to a generator. 
  • A way to turn the electricity into light (a bulb). Light bulbs come in a wide variety of shapes, sizes and technologies. 
  • A way to get the electricity to the bulb. This would be the wire and switch. 

    The simplest light circuit would be a bulb like this: a 12 V turn signal from a motorcycle. This is a common 1156 bulb found in a lot of automobile turn signals.

    Hooked up to a battery like this:
    Two 6 V batteries from old "Exit" signs in series (to provide 12 V)

    With wire like this:
    A piece of extension cord that got run over by a lawnmower. (Yeah, I recycle a lot of things). Since we're not dealing with a lot of amps, this wire (16 ga.) could be a lot longer and still be safe.

    Here are the three put together.
    Almost- the positive wire isn't attached yet.

    Let there be light!

    You may have noticed that the batteries had some writing on them. They are sealed (won't spill) lead-acid (rechargeable) 6V, 4.5 Amp Hour batteries. I've covered the type and voltage already, but what is an Amp Hour? An Amp Hour is a measure of how much power a battery has in it over time. In the batteries I'm using, it is calculated over a 20 hour period, so (time to break out the algebra) 4.5 AH / 20 Hours = 0.225 Amps. Since 0.225 is awkward to use, most of the time Amperage is given in milliamps (1/1000th of an Amp), so we can expect this battery to put out 225 mA at 6V for 20 hours (roughly). You can get more amperage out of them, but they won't last as long- the 4.5 AH is a constant.

    To put this in perspective, a common car battery is in the neighborhood of 100 AH capacity, but they are not designed for deep discharge like a backup battery is. Repeated discharge and recharge of a car battery causes them to fail internally due to the way they are built. They're designed to put out a large jolt for a short time to get an engine started, not run the car. Golf cart batteries, marine (trolling motor) batteries, and forklift batteries are examples of "deep cycle" batteries that are designed to be run down and recharged often.

    I mentioned that the bulb in the first picture was a common one:
    • Type 1156 bulbs are used as turn signals (front) and have only one filament in them. They usually have a single wire coming out of the socket, the body of the socket is the other conductor (usually the negative side, which is standard for automobiles- the body and frame is the "ground" and hooked up to the negative battery post). 
    • Type 1157 bulbs are used for turn and brake lights (rear), so they have two filaments in them, and usually have two wires coming out of the socket, the body again being the negative conductor. One filament is larger than the other and will put out more light. 
    To compare the two, The 1156 uses 2.1 A at 12 V (25W) while the 1157 uses either 0.6 A (8 W) or 2.1 A (25 W), depending on which filament you wire to. Hooked up to my little 4.5 AH batteries, I could expect to get about 2 hours of light from the higher intensity light (4.5 AH / 2.1A = 2.14 hours), or about 7.5 hours on the lower intensity filament (4.5 AH / 0.6 A = 7.5 hours).
    Data on commonly found bulbs can be found here.

    There is another option that is getting more common - LED replacement bulbs. They use about the same amperage of a regular bulb, but they last longer, and are less fragile. The up-front cost is much higher, though.

    Next week I'll play around some more and explore a few more aspects of DC electricity.

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