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For those experimenters that are continually on the go, and need a mobile power source that could be lugged about. I offer you the Big Bad Battery Box.

Step 1: Finally Getting Around to Filling the Decade Long Need for Power

A number of years ago I started toying with homemade VLF (Very Low Frequency) radio equipment. These radios covered a range of roughly 10Hz to around 10 KHz and to aid in reception with minimal noise, I needed to place myself and the equipment far away from manmade electrical interference. This meant going far away from the electrical grid for long periods of time.

As time marched on, it would seem that my need for portable power increased almost tenfold. I have many projects doing many different things, and I always seem to need power in places that scarcely offer it. (i.e. satellite/space station communication, VLF monitoring, geophone monitoring, watching satellite TV in the middle of nowhere, you get the picture).

To facilitate all of this I needed a luggable and robust power source at a minimum of cost.
 

Step 2: So What Did I Have on Hand?

Because this need for mobile power has continued for nearly a decade and a half, I happen to have a few parts lying about.

First up is the box. I picked this gem up from one of my regular haunts. It was basically just an empty box that at one time housed a Wheatstone bridge. The store clearly exploited my weakness for rugged wooden boxes.

I found a power supply that fit neatly into the box only one isle over from the box. The total cost of both items was somewhere around eight dollars in 1996.

Poking around a little further in my garage, I turned up a few lead acid batteries. These are two 4.5 Amp Hr 12 Volt lead acid batteries. I pulled these from a small electric scooter a few years ago and could not bring myself to dispose of them.
 

Step 3: Ok, Now That I Have a Bunch of Parts, What the Hell Do I Do With Them?

Well first you want to assemble all the team members to see how things would be mounted and wired together.

The basic ideal was this. I wanted a box that contained, one variable power supply, both lead acid batteries, and a power connector. Each item would have its own power hook-ups. This way the box is multi-purpose. If near an outlet I can use the power supply, if not I can use the batteries in series or parallel, the power connector can be hooked up to either the batteries or the power supply. This configuration also allowed me to use the power supply to charge the batteries.

Score one for me.

Step 4: Solving for the Variable

The problem I now faced was how to make the power supply variable. I am sure there are many ways to do this and Lord knows the way I choose is not nearly as efficient as it should be. However I only was able to use what I had on hand and to make it work for me.

The picture below shows voltage regulators. They basically take a larger voltage and make a stable lower voltage, regardless of the load you place on them (Well, sort off).

The voltages I have on this unit are as follows 5, 8,12,15,18, and 20. The power supply provides around 21 volts. I wired these up to a 12 position selector switch.

In the second picture you can see everything all wired up. Be sure to make your lengths of wire consistent with how everything will be mounted in the box.

Once everything was soldered together it was time for a test. I checked each of the voltages and they all came out to be right on the nose.
 

Step 5: Putting on a Decent Face.

Finally I had to make things look nice. I used an old piece of paneling from one of our daughter's walls as a face plate. I cut holes, sanding it down, and sprayed four coats of enamel on it.

Step 6: Presenting the Big Bad Battery Box!

I am pleased.

Now I just need enough time from all the events in my life to take advantage of my latitude this winter to see if I can catch some of the Northern Lights on my little receiver that will now have PORTABLE POWER!!!!
<p>The store clearly exploited my weakness for rugged wooden boxes.</p><p>Too funny!</p>
Can u post a circuit diagram...i am planning to build it from scratch.. any suggestions for that?
Very clever, good work!

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Bio: I like to tinker and I like to learn, and if one can support the other then thats great.
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