Alt-Power Battery Box


The solar panels harvest energy during the day, and store the energy in my bank of golf cart batteries.  At the last house, and currently at this one, the batteries live on a heavy duty workbench inside the garage.  The upside is the batteries are easy to maintain.  The downside is they off-gas when charged.  Usually it's such a small amount, in a two car garage, it's not detectible.  But when a battery gets old and fails, they can draw a large amount of current due to the shorted cells.  The battery gets hot, boils off the water, and stinks up the garage with explosive hydrogen sulfide gas.  Not good.

I've since decided to move the entire battery bank outdoors.  Since I'm in FL, cold weather is rarely an issue.  It does get hot outside, but it's as hot in the garage.  If you consider how hot the engine compartment is a 90 degree box or garage is no big deal.  I've been getting 5-6 years of useful service from golf cart batteries.

To minimize the length of batteries cables from the battery bank, to the inverters, I located the battery box to opposite side of the wall where they live now.  The cables will enter the house via a conduit.  A couple of vents were added to the box and a small fan was installed.  The fan will be solar powered, and only run during daylight hours, when the batteries will off-gas.

This is yet another on-going project, so check back to see the progress.


I bought a used heavy duty aluminum box from a salvage yard.  I later cut the handles off.  But to water the batteries, it's way too low.

To get the batteries up to the height of my workbench, I designed a simple frame to mount the box upon.

That's pretty close to the ideal height for me.

The frame is 1" square tubing.  I used a MIG welder to fabricate it.

All welded up.

I have a Harbor Freight hoist in the attic that I use to install/remove the hardtop from the Jeep.  It works well to lift things like this frame, to make painting much easier.

I could have welded the ends of the box channel closed, but these nifty plastic plugs work fine.

This is where it'll live.  Time to cut the handles off, cut a 4" hole on each end for ventilation, paint the inside of the box with truck bedliner coating, and spray the outside of the box with a paint that blends with the outside of the house.

Now to install the vents, the fan, and paint the outside.

The box construction is complete.  The fan I'm using is a 4" 12VDC box fan.  It's moving too much air.  Audible even from 10' away.  I'll put a smaller fan inside.

Next will be to pour a 4'x3' concrete slab and secure the frame to the slab.  Went to Home Depot this morning to pick up nine 60 lb bags of concrete, a pack of stakes, and a couple of 1"x4"x8' pieces of pressure treated lumber.  Less than $40 worth of material.  The wood will be used to make a form to shape the concrete, then reused for other projects.


Too wet yesterday.

Got a break in the weather this morning.  Supposed to rain later, so had to get started.  A basic 3'x4' frame.

Nifty little trick I came up with was to put Tapcon screws into the existing concrete to give the new slab something to hold onto.  This prevents the new slab from pulling away from the existing one.  A total of 6 were used.  You can spot the concrete dust in the previous picture to see the placement.

Because of the wet weather yesterday, the 9 bags of concrete we put on my lawn cart, and stored in the garage overnight.

I used an Odjob mixing barrel to stir the concrete.  Put in 2 lids worth of water, dump in the 60# bag of concrete, screw on the lid, tip it over, then roll it about 10' one direction, then back.  Unscrew the lid, pour the concrete.  Really very simple.

The first mix was a little dry, so the following mixes I added a little more water.  A slightly wet mix levels easier.

That looks about right.

The only difficulty in this mixing barrel is that it's difficult to grab once the lid is removed.  I do take the time to clean the inside of the barrel and lid between bags.  If concrete is left on the lip of the barrel, the lid becomes very difficult to remove.

A float was used to push the aggregate down, forcing the cream (wet slurry) to the surface.  This job took almost 8 bags to complete.  I tried to keep the concrete from splattering against the painted wall, but some touch-up painting will be needed.

All smoothed out, and the edges that will be exposed have been rounded over.  It will harden overnight, and the frame can be removed tomorrow.

I used a tarp over the wet concrete until it set a bit.  The form was removed.  It'll lighten as it cures.

The box and stand were placed in position, and a long drill bit punched through the box, and made a mark on the stucco.  I then moved the box, and used a masonry bit to bore through the 1/4" concrete, all the way through the wall, and the drywall on the far side.

For $8, I bought a set of hole saws from Harbor Freight a while back.  They work surprisingly well, despite the price.  It cut through the aluminum box easily, but the stucco was another story.

I knew I'd trash the bit, but it's a lot cheaper wasting a cheap bit, than buying a 3" masonry hole saw.

It ate through most of the stucco before throwing sparks, and it stopped progressing through the wall.  A hammer knocked out what little stucco hadn't been cut with the bit, and the foam board behind it.

The dead hole saw on the left.  It once had teeth like the one on the right.

Since the 3" bit was now history, I grabbed the next higher size from the kit.  A 4" hole was made where the pilot bit punched through the entire wall.

Now the outside hole lines up with the inside one.

The bus bars were moved up a few inches to allow another 4" hole to be cut inside the cabinet.  A wire fish was run from the upper hole, to the lower.  The battery cables can be pulled up through the wall, and pushed to the box on the outside.  When complete, a cover plate will be placed over the lower hole

A 4" platform will be placed in the bottom of the box.  The conduit and wiring will fit below the platform.

The old battery bank slowly died 5-6 years after installation.  That's about all that can be asked from golf cart batteries in the Florida heat.  When my budget permits, I'll buy 8 new ones.  Lot to do before then.

Four sets of batteries cables were built.  I'm using Anderson 175A quick disconnect plugs.  The cables are 2 gauge welding cable.  Since the batteries share the load, each cable will see about 50A with the 1800W inverter under full load (200A @ 12VDC).

The cables were fished through the conduit, up inside the wall, and into the back of the Alt-Power panel.


To get the batteries up high enough to easily work on, a wooden deck was added inside the box.  The lower section was made from scrap 2x4s.

The upper portion is 5/8" plywood, secured with deck screws.  It'll easily support the weight of the batteries.


The outdoor battery box is complete.  Ready for batteries.

The old batteries were taken to the local Sam's Club, and exchanged for a new set of golf cart batteries.  $85 each, but should last 5-6 years, like the previous set.  The energy savings will more than pay for them.

These are what I chose.  Standard GC2 batteries.  I would have liked to have purchased AGM batteries, but those were more than twice as much.

Hey, they're actually made in the U.S.A.!

Each battery weighs about 70 lbs.  The box I found at the scrap yard is the perfect size for these 8 batteries.

Each battery was topped up with distilled water, a fuse installed on the positive terminal of each battery pair, and wired into the system.

Inside the garage, the Iota 75A charger has started charging the new battery bank.  Already dropped down to a 34A charge rate.

The finished project... for now.  520 Watts of panels on the roof.  Another 480 Watts of panels yet to be installed.  Tomorrow morning I'll get the charge controller wired up and take the Iota charger off line.

Very pleased with the battery box.  No worries of flammable fumes building up in the garage, and each battery pair is fused at the battery.  The box is also the ideal height for me to periodically water and clean them.


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Last updated 11/09/13    All rights reserved.