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This is the most popular book for PV remote homes. It is written and published by

Fowler Solar Electric Inc.

"Best all around book on wiring your PV

system."

1991 Real Goods Sourcebook "Our favorite book for Do-It-Yourselfers."

Windy Dankoff, Flowlight Solar Power "This should become the bible for alternative energy users.

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Building a Battery Box

Bill Battagin

©1994 Bill Battagin

We folks who choose a photovoltaic system as our source of power, enter a relationship much like that we enjoy/endure with our significant other. Sunshine and smiles have long been associated as a symbiotic pair. Occasionally the system (or "Honey") blows a fuse, right? We need to be ready! The design, sense of safety, and construction of my new battery box evolved from living with a photovoltaic system for the last ten years.

In the beginning there was (sun)light

When photovoltaics entered my life, I was a novice concerning electrical wiring, batteries, metering, balance of systems, inverters, and so on. Eagerly, I forged ahead with tape, glue, and bailing wire in hand. At the time I felt my installation was copacetic and safe. Now, though the upgrades made on my system are still fueled by "PV dreams", they are more sophisticated and based on knowledge and experience.

"Drive carefully, Honey"

Safety is the foremost reason that a battery should be enclosed in an appropriate container. Why not just plop them heavy little buggers in some back room somewhere out of the way, bolt a few wires to 'em, and forget it? Well, a battery generates hydrogen gas which is explosive and contains sulfuric acid which can burn skin, eyes, and other parts of biological units. The acid can corrode your once beautiful looking terminals, cables, joints, and surroundings. We've been told before, it's something we already know: a battery (like that boyfriend) can be obnoxious.

So from a safety standpoint, a battery needs to be kept away from and inaccessible to people of all ages. Your enclosure should be able to contain acid in the event of a spill or leakage. It should also collect hydrogen gas and vent it to a safe outside location.

Cost of Bill Battagin's Battery Box

Equipment

Cost

Copper bus bar, 1/0 cable, interconnects

$65

Hot air ducting & 12 V fan

$74

1/8 inch Acrylic sheet (4 feet x 4 feet)

$55

1/4 inch AC plywood (4 feet x 8 feet)

$15

One pint each primer, paint, & linseed oil

$10

Misc. caulk, screws, nails, slide bolts

$9

Fiberglass insulation, R-11

$5

Lumber, recycled

$0

1 inch PVC pipe, recycled

$0

Three door hinges, recycled

$0

Total

Performance! You want to get the most from your new battery. I chose eight 6 Volt L-16 wrapped-plate lead-acid batteries manufactured by U.S. Energy (1400 Amp-hours at 12 Volts). Somehow when we install our spiffy new (or used) battery bank, we think that we're done! These puppies will last forever. Not! It will be too soon that you are elbows deep in battery cables and sulfuric acid again, changing them out. So we want to get as many miles as we can from this expensive investment. The way you connect your battery, the gauge and materials of your conductors, and the integrity of the electrical connections at your terminals all make a difference. For these low voltage systems, any resistance created by poor connections, too small a wire gauge, and the yuk that builds up means less juice reaches the battery. Keeping dirt and other contaminants away from your battery and connections will increase performance and lifespan.

Another function of a battery enclosure is to regulate the temperature of your bank. That location on the floor, in the back room, in the basement, or outside that you chose for your battery may have satisfied most of their needs. But in the winter, it (she) likes to be warm, in the 70°F range. Don't locate the battery where it will get too warm (over 90°F). Winter warming will have a significant effect on performance, believe me!

Living together

Whether your battery lives inside or outside your home will be determined by many factors: proximity to the PV array (or other energy source) and the inverter, space availability, considerations for venting hydrogen, ease of maintenance, and a method of adding heat to the battery bank. I like the concept of a small power/battery shed separate from my house, but it would increase the cost of my system in time and money. An inside location can be safe and functional, if done properly. And it's definitely easier to add heat.

©1994 Bill Battagin

2x2s for securing acrylic tray

^Jx6 siding

R-11 fiberglass x I insulation 1/4" plywood

3/4" AC plywood

_ Three 2x4 " shelf supports 2x4

Cripple studs

Exhaust vent

3/4" AC plywood

_ Three 2x4 " shelf supports 2x4

Cripple studs

Exhaust vent

2x2s for securing acrylic tray

The previous relationship

My last battery bank consisted of twelve 220 Amp-hour U.S. Energy 6 Volt golf cart batteries which lasted about five years. At 1320 Amp-hours in a 12 Volt configuration, the battery bank gave me about a five to six day storage capacity. My C/40 rate for charging (my 11 photovoltaic modules deliver 33 Amps) seemed to treat the battery with respect. In any big emergency I still use my grid connection for back-up. I chose to stay with a lead-acid battery because it is recyclable and easily obtainable. Eight L-16 batteries require fewer connections, cables, and joints than a comparable nickel-cadmium battery bank. The space required for a nickel-cadmium bank is significantly larger, since they have a lower energy density. Finally, I found a good deal on these L-16s. This new bank gives me a bit more storage at 1400 Amp-hours. We could talk about usable storage (you should only discharge lead-acids 50-80% whereas nickel-cadmiums can be fully discharged), but uh, I hear my mom calling Onward!

Making it work

My battery box was constructed somewhat like a closet. My brother, Dr. Goose, built the four inch stud frame construction walls, insulated and put exterior siding on them. The exterior siding was once the

^Jx6 siding

R-11 fiberglass x I insulation 1/4" plywood

decking for a roof, some nice looking 1x6 Douglas fir. Four L-16s weigh about 536 pounds so he installed cripple studs under the end support for the three horizontal 2x4s that support the batteries. The door on the box is also four inches thick and is large to allow easy access (see diagram left). The walls, ceiling and door are insulated to R-11, with an inside sheathing of 1/4 inch AC plywood. The existing south wall in the utility room is the back wall of the battery box.

I primed and painted the plywood with a high quality enamel paint. Though certainly not acid proof, it would safely shed any vagrant acid down to a 1/8 inch thick acrylic "tray" in the bottom of the box. The tray is the length and width of the box by ten inches tall, large enough to contain all the acid in one battery. To build the tray, cut the bottom (18 by 33 inches), two sides (10 by 33 inches), and two ends (10 by 18 inches) from a 48 by 48 inch sheet. The bottom of the box had plenty of backing and nailers to solidly support the acrylic sheets which formed the tray. Holes were predrilled and countersunk for the 1 5/8 inch sheet rock screws which secure these pieces to the walls and floor. All corners, screw heads, cracks and penetrations were caulked with 100% silicone seal.

Must have been something I ate

I dealt with hydrogen gas in two ways. First, I installed Hydrocap battery tops on all the cells. Voila, 90% less hydrogen to worry about. Second, a one inch PVC pipe exits the top of the box to allow any gas to escape to the great outdoors (would you please do that outside?) Remember that a hydrogen vent pipe must always rise upward. Horizontal runs should have a little slope so the gas rises to an elevated location, away from ignition sources. Another feature of Hydrocaps is less yuk to clean off the top of your batteries and your terminals and cable connections. I love it. Wiring to and from the inverter, controller, and loads is caulked where it penetrates the walls.

Keepin' her warm

I built my battery box in a back room of my house, a utility/shop space on the north side of the house. It's a cool place — my refrigerator lives there. But batteries perform better at warm temperatures, especially lead acids (see HP#9, page 25-26 for a temperature comparison of lead acid batteries). Cold lead acid batteries (at 40°F) have only 80% effective capacity than at 78°F — having cold batteries is like removing some of the batteries from your bank!

To bring my batteries up to a happy temperature, I installed four inch insulated ducting at the ceiling above my woodstove. This vent comes into the top of the battery box and then enters a sheet metal enclosure inside the top. This enclosure drops about ten inches down into the box and is six inches square. On one side of the enclosure towards the bottom, I cut a 3 1/2 inch round hole where I attached a 12 Volt DC brushless fan. I mounted the fan below the top of the box to prevent hydrogen gas from entering this duct. The fan draws 80-90°F air heated by the woodstove (it's best to pull with a fan, not push) into battery box, warming the batteries. Cool air is exhausted into the room at the bottom of the box on the opposite side.

The uniform heating of all cells was considered in this design. Some baffling may be required after further testing. At this point, I manually turn on and off the fan (on at 10 PM and off at 7 AM), but my mind is conjuring up some schemes for an automatic system.

Solar heating is a viable option. I heat the battery for the solar electric system at my store with a solar hot air panel using a sun synchronous DC fan ducted into my exterior add-on battery box. It works like a champ.

Good Connections

Following Richard's instructions in HP#7, page 36-37, I made and soldered ends onto 1/0 welding cable for my interconnects. Basically, I used short (about 2 inch) pieces of soft copper tubing, stuffed a stripped end of

Positive Copper bus bar

PV input _ via SCI ^ charge cm controller ""

Positive Copper bus bar

PV input _ via SCI ^ charge cm controller ""

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