Building a battery box

BoFuller · March 2015

Later this week I should have 16 Trojan L16RE-B's delivered. I'm planning on making two boxes, each 6 feet long, 18 inches wide and 28 inches deep, with a floor 4 inches above the shed floor, leaving 24" for the batteries. They are 18" high, leaving 6 inches for cabling, and wires going to panels and controller/inverter. Is this too much room? Not enough? This would allow for about 4-5 inches between each battery. I'm planning on cutting a hole in the end of each box, putting a fan at the end of one, blowing outside, with the far opposite end open to a vent for allowing fresh air in.
Am I missing anything? Construction to start Tuesday morning.

706jim · March 2015

The battery box sounds fine.
However, you are going to get blasted here for not having enough panels for that substantial battery bank.

BoFuller · March 2015

Okay, I need to update my sig info. That is what I have on my trailer. I'm finally finishing my log home and the 16 batteries are for it. Along with 12 Kyocera 235 panels on the roof and a 3648 a Outback. Also a Generac 11K propane backup generator.

BB. · March 2015

Make sure you log the temperature corrected Specific Gravity (for each cell, and check electrolyte levels to make sure all plates are covered) and the battery resting voltage as you receive them (label each battery so you can keep track of the readings).

There has been issues sometimes when the batteries get installed and things are not working right--And cannot be sure if it started with a bad cell/battery/improperly charged and shipped, or if it was something else.

-Bill

Photowhit · March 2015

When constructing the battery box, I would be sure to make one of the long sides detachable, those are not fun batteries to lift over such a height, I'm not sure why you don't just do one box with both strings in it?

If they are next to each other it will be a pain to take readings for the far box.

I planned on leaving 1" between the batteries on my old battery box (before junking the plan to use multiple strings and going with a forklift type battery). I think Trojan recommended 1" between batteries...

sub3marathonman · March 2015

Photowhit wrote: »

I'm not sure why you don't just do one box with both strings in it?

For my battery setup, I had them in a corner, so it ended up being L shaped, which worked out fine.

I also used pegboard on the front to give a bit more air exchange, although I don't know if it really mattered much. But it looks nice.

Vic · March 2015

Hi Bo,

OK, guessing a bit ... So, you will have two strings of L-16s in parallel on a 48 V system (we hope). Assuming more, each string will be in its own battery box.

Have built insulated plywood battery boxes, similar to what you are describing -- three inches of foam insulation in the box floor, 2X4s on edge for strength every two feet or so. This also boosts the batteries by 4+ inches with the 1 1/8" plywood floor. Insulated the sides and the hinged cover with 2, or 3 inch foam. Have two 4" air inlets at the bottom of the box, and the exit at the very top of the box.

Placed the BTSes for all charge sources on a single battery, under a 2" piece of Styrofoam sheet - hogged out to allow all sensors to nest comfortably under that sheet.

One possible issue with multiple strings of batteries, especially when they (may be?) each in their own battery box, is temperature variations between each string, and the pesky question of, just WHERE to place the BTSes. Temperature compensation can be very important for the health and good charging of batteries, and trying to allow all of the batteries to attain a fairly consistent temperature is key, IMO.

Agree with the comment, that the front of battery boxes need to be easily removeable (we use about six bolts into "T-Nuts" to accomplish this. With just a nominal 4"step up, into the battery box, is was very easy for one person (yours truly) to place each battery (315 Lbs each). No need to lift them, just used a hand-truck.

You may not need 4-5 inches between each battery, and this space may require somewhat longer interconnecting battery cables. All is a trade-off.

FWIW. Good Luck

BoFuller · March 2015

Ok, I think I'll cut it down to 8 ft and make it about 24 inches wide so I can put in two rows of batteries. Less cables, more consistent temps, more equal charging. I like the idea about the removable front!
Since the shed is well insulated (top, bottom, and all sides), do I still need to insulate the box?

Thanks for all the responses.

BB. · March 2015

Make the insulation something you can add/remove at will (something like foamed sheet insulation/no aluminum foil--possible shorts and acid mist+aluminum).

Monitor the battery bank (through the seasons) and add/remove insulation as needed to keep the operating temperature range you need. Batteries will generate heat when cycling--Insulation will keep average temperature higher when cycling. Batteries setting unused will slowly get colder--Which may be a good thing--They age slower (~2x longer life for every 10C drop in temperature) and will not freeze at any reasonable temperature if stored mostly charged.

-Bill

Vic · March 2015

Hi Bo,

As before, there are a number of tradeoffs. There can be quite a bit of heat that is dumped into a "power room". So an insulated room can retain quite a bit of this heat, as it can be more difficult for the room to cool at night, with the usual over-night lower temperatures. You may have temperature inversions on Summer nights, so the nights may not really be that cool.

An insulated battery box can make it more difficult for the battery to cool during evening hours, etc, Flooded batteries can heat considerably in the Absorb and EQ stages so box insulation will trap this heat for some period of time.

The systems in use here are in insulated power rooms, and the batteries are in insulated boxes. This was the initial approach. After a year, decided to add a 6 K BTU window A/C to the power room, and now leave the hinged lid to the batt box open at all times. The room has some natural convection ventilation, with the exit vent at the ceiling. You may wish to use the fan-forced ventilation, of course, it may be a bit safer.

One could probably try to exchange (often) cooler evening/night air with power room air on warm days, but the A/C is kind of an opportunity load, although it is not uncommon for it to cycle, all night with reducing frequency. The A/C uses about 500 watt-hours when running. May try a larger 10 - 12KBTU unit for some added cooling (added some more PV last year).

Am not certain that I would insulate the sides and top cover again, although is might well help the batteries to reach a more consistent temperature, verses having no insulation even with no top cover / lid. Cooler batteries are happier batteries ... perhaps with some limits in Winter.

A number of people recommend about two inch separation between each battery, and about the same from battery case to side walls of the box.

The only additional thing to mention is the fairly obvious issue of being able to see into the battery vent wells in the rear row of cells. On the best-insulated box here (also the box with a bit more spacing, the last cell row is a bit of a pain to see into. It just requires a bit of leaning. This may be one of the reasons that you were considering two separate boxes ... More space between batteries can make this a bit more difficult. ... tradeoffs.

More opinions. FWIW, Vic

BoFuller · March 2015

Thanks for all the good info. I hope to start constructing tomorrow.

Building a battery box

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