Battery enclosures and NEC [RE-wrenches]

[Allan Sindelar]

John, maybe a little of this might help.

I use plywood too, because it's familiar, available, and works, and because
I worked 20 years as a carpenter/woodworker in a former life.

For many sets of batteries, 4' x 8' is an awkward dimension. 4 L-16s require
about 50-52" in one dimension, which leaves a lot of scrap. What I have had
great success with is a type of plywood called "Baltic Birch", that is
commonly used for better cabinet drawer carcases. It comes in 5' x 5'
sheets, so the waste is minimal. The 1/2" material has nine plies, so it's
very easy to glue and fasten to and very dimensionally stable. These
features also let it almost double as furniture or cabinetry, as it finishes
well and looks very professional. We get it through lumber wholesalers, not
retail yards; in our area it's delivered. It costs $30-40/sheet, and two
sheets pretty much does one typical box if carefully laid out.

For a relatively inexpensive liner, try "pond liner" at Home Despot. It's
about $15/linear foot, but is some 10' wide, so one length does two boxes. I
have seen both PVC and EPDM sold as pond liner; I think the EPDM is less
toxic to the environment, both in manufacture and disposal.

We put battery boxes indoors whenever we can, in either a heated or at least
a tempered space. This is to maintain effective capacity during winter by
keeping the batteries warmer. We always use a Power Vent to control
ventilation and prevent backdraft. I will often add a toe-kick base to my
battery boxes, similar to a kitchen base cabinet. It makes servicing the
batteries much easier, to be able to stand close to the box.

I have never understood the point of insulating a battery box, and I wish
someone would explain it to me. In RE applications during cold weather, the
charging process creates a negligible amount of heat. If the batteries are
in an unheated space, and there's no source of heat to keep them warm, they
will eventually settle at the average seasonal ambient temperature of the
space where the box is located. Insulation only slows the rate at which the
cool off and warm up; they'll eventually reach the same temperature with or
without the insulation. So what am I missing here?

Allan at Positive Energy

----- Original Message ----- 
From: "John Raynes" <john at raynes.com>
>
> Thanks all for the great feedback to my earlier questions.
>
> One additional question I have about "site-built" fiberglass or HDPE
> liners fabricated from sheet stock:  By definition, there are gaps
> between the bottom deck and the side lips.  What's the best
> acid-resistant caulk material to use to seal those interfaces?
>
> We've looked at the pre-fab spill containment trays from time to time,
> our problem is that it costs at least as much and perhaps even more to
> ship than the item itself costs, and there's so many variations on
> battery sizes, orientations, etc.  That same rule about buying pre-fab
> also applies to battery boxes unless they can be broken down for
> shipping.  We're 10 hours drive from the nearest full line solar
> distributor, 3 hours from the nearest freight depot so we rarely pick
> up anything ourselves, and all freight is interlined.
>
> I hear Jeff's comments about moving to commercially built boxes
> someday, but they add significant expense, even without the shipping
> costs.  I would hope for a compromise solution where construction
> techniques and materials are more fully specified for all important
> details, such as acid resistance, flame retardancy, strength, back
> draft protection, no access without a tool, etc.
>
> We build our enclosures out of 3/4 plywood for the deck, 1/2 OSB sides
> and top, with 1-1/2 to 2 inches of foam all around.  We rip framing
> lumber into appropriate sizes for strength and fastening support on all
> edges.  I try to avoid site built wherever possible, so I have a basic
> design that breaks down into  6 or 7 flat pieces for transport to site.
>   If I can pre-build at the shop things always turns out better.  That
> pretty much applies to everything we do.
>
> At 10:37 AM 10/4/2007 -0700, you wrote:
>
> We started out building tight battery boxes for all our projects which
> included a lock hasp on the cover door, but finally switched over to
> battery "rooms".
>
> We now work with the builder or architect on new construction to
> include a long and narrow room dedicated for only the batteries, with
> the inverter on a the outside wall surface for this room. The room is
> constructed of heavier fire-rated green-board drywall on the interior
> walls and ceiling, a concrete floor with floor drain, and a DC in line
> exhaust fan located at the highest point and powered from the inverter.
> We also add a fire extinguisher and safety signage on the access door
> which is locked.
>
> When we switched away from battery boxes, all our past battery and
> battery cable corrosion problems dis-appeared. The tight battery boxes
> were providing an very acid-rich environment that would destroy battery
> cables in less than 3 years, not to mention the piles of corrosion we
> had to clean off each year. Now when I check on an older battery room
> system, you could eat off the floor and the battery terminals are as
> clean as they day they were installed.
>
> I think the days of site-built battery boxes are numbered, most likely
> when the NEC takes a look at the safety issues of many poorly
> constructed site built boxes that are out there now. It would not
> surprise me if battery boxes will someday need to be commercially made
> and tested to some kind of UL listing that addresses proper venting,
> door safety, drains, door seals, fire-rated materials, explosive
> containment, and include a certification label on the cover. Just my 2
> cents.....
>
> Jeff Yago, NABCEP Certified DTI Solar


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