How To Build A Battery Bank Box On The Cheap

It's one thing to "go green" with a bank of twelve volt batteries powered by a wind turbine but quite another to figure out how to do that without breaking the bank at the same time. My wife and I moved onto our remote desert acreage in April and soon decided wind was the way to go. But....

When you read about electrical power produced via small wind turbines, you find articles wherein the authors express delight at their economical installations. We're not talking about the books for sale online which boast that you can make your own power for two or three hundred bucks. Maybe you can; maybe you can't. One thing is for sure: Whoever is selling the books will make a few bucks. However, those are promoting plans to allow the homeowner to build his/her own system from almost nothing. I'm not interested in those. One does amuse me considerably, and that's the one promising to tell you (among other things) how to "get 25 free batteries".

Uh-huh. That may well be possible, but anyone who's ever been an auto mechanic knows that you're asking for trouble if you're using unmatched batteries in sets such as the battery bank groupings which are the heart and Soul of any solar or wind power system. You may very well get 'em for free...and if you do, they'll be worth exactly what you paid for them.

No, I wanted a wind turbine, but a commercial model. Such systems can cost around $30,000 easily enough, with some homeowners feeling very proud of themselves for managing an installation that cost only $16,000.

Again, "Uh-huh."

Having to spend that much money made no more sense to me than being able to get off scot free. After studying equipment components available online for several months, I began to believe a solid system could be installed for something like $2,500...if everything went right. Will that number pan out? We'll let you know after the system is up and running. Right now, things seem to be on target. The turbine, controller, and inverter have all been ordered and paid for. The batteries were picked up from Sam's Club in Tucson for $638 (including tax and rounded to the nearest dollar). A watt meter to measure turbine output is also on order, and tomorrow I'll be calling suppliers to see about ordering the necessary battery cables.

The batteries themselves are made by Interstate, a brand Pam and I both know and trust since Interstate batteries are common in the trucking industry. They're not twelve volt units, however, but rather six volt deep cycle units made for powering golf carts. Connected properly, eight six volt batteries will soon become four twelve volt batteries and provide 840 amp hours of reserve power.

But they needed a home.

Don't you just love it when a salesman asks you, "What would you like to spend?" When it comes to containers designed to house a battery bank, commercial versions are definitely available...for two or three hundred bucks. Not to mention, good luck finding exactly the right container for your exact application. In our case, it took a trip to Home Depot and another to Wal-Mart. At Home Depot, a seven dollar sheet of wafer board sheathing plus a number of pieces of cull 2" x 4" lumber did the trick. Add a cheap gallon of paint and an even cheaper set of paint brushes from Wal-Mart, and our bank battery box cost roughly $20 total. True, that didn't count the decking screws which we already had on hand.

First phase: Building a sturdy base/floor for the box. The floor board was cut two feet deep and four feet wide. Five two foot lengths of 2" x 4" were placed under the board on edge at even intervals and fastened in place with plenty of 1 1/4" decking screws. One thing we've acquired over the years has been a great supply of power drills, so I use two: One loaded with a small bit for drilling pilot holes, the other (the variable speed version) holding a Phillips head screwdriver bit to make screwing things down tight a piece of cake.

When my wife learned that my original intention had been to build the box as a sort of "open shelving" arrangement, she suggested (gently!) that I might want to reconsider. Our monsoon rains can hit the ground hard enough to splash mud up pretty high, even under the back end of the storage semi trailer where the battery bank will eventually be installed. Hey, when she's right, she's right. So I mentally tipped the design ninety degrees, producing a box with closed sides but an open top.

First, though, I needed to know that the batteries were truly going to fit where they'd been designed to fit. High powered hotshots often rely on measurements to figure that out. I don't. I'm an old rancher's son, and country folks learn early not to take much of anything for granted. As soon as a couple of pieces could be put in place, I needed to actually place two of the batteries in position.

I was wrong, I was right, and I lucked out. According to the numbers, there should have been about 3/8" of open space between the batteries and the lower 2" x 4" pieces of lumber. Unfortunately, I'd procrastinated for more than a week after getting the lumber home from Home Depot, and some of the precut 2" x 4" chunks of wood had warped. Additionally, the length measurement of the batteries was not quite accurate; these particular products have a slight "bow" in the center of the ends on each battery case. Net result: Lost free space, times two.

Luck did win the day with 1/16" of free space actually remaining. Whew! (Imagine how frustrating it would have been if I'd built the whole thing without checking...and the fit missed by 1/16"! What a revolting situation that would have been!)

Okay, now the sides. I found it easiest to attach the sides by standing the project on one end. First one side (naturally), then the other. That turned out to be about the easiest part of the whole project, went lickety split and looked like something was actually happening to boot. When it came to installing the end boards, the glitch factor was back. Nothing serious, but the boards--which had been precut at Home Depot--were a little too wide. Not Home Depot's fault. Their sawyer and I had attempted to get exact two-foot dimensions, but the longer boards came out a little narrower. It didn't take much thinking to know why: The square pieces were exactly on target, but we'd had to make an additional cut to produce the long boards, and the result was a misfit by the width of a Home Depot saw blade.

I would have used a Skilsaw to trim the edges, but both such saws (yes, we have two) are buried in a box somewhere in that forty foot semi full of household goods. The box is clearly labeled, "Two Skilsaws", but precisely where it might be remains an open question. In the end, it didn't matter. Wafer board is easy to cut, even with a slightly dull and somewhat aged handsaw.

Once the trimming was accomplished, the fit was perfect. Note: The end boards are not firmly secured but, after being painted, were simply tacked in position to temporarily encourage the overall box to hold its proper shape. The controller will be mounted on the left end board and the inverter will be mounted on the right end board. It will be a lot easier to do that without the boards being part of the box at the time. Equally important is the fact that I'd be asking for a rupture and a cracked skull if I were to try lifting those heavy batteries over the top edge of the box while bent over underneath the back of that semi trailer. This way, I can slide the batteries into place through the open ends, then place the end boards in position (with electronics attached) and then cinch everything down.

I'll only need to bend over the top of the box to fasten the battery cables that connect the controller and inverter to the battery bank, and that's doable.

 The completed box, two feet by two feet by four feet, looks pretty good.  It needs a little protection from the weather, of course.  Sun and rain will have only limited access, since the container will reside dead center under the back end of the semi trailer, but any raw lumber needs to hide from the elements a little bit...and wafer board is even more vulnerable than that.

It's a good thing Wal-Mart has low cost paint, because this thirsty box drank down a solid half gallon of battleship gray without stopping for breath.  If I'd been feeling generous, it might have accepted that much again.  At least it's well sealed now, and that's the point.

Once the the controller and inverter arrive and have been mounted on their respective end boards, we should be within a day or  two of actually  generating our own electrical power.  We'll keep you posted.