Building A Battery Box

[Freesail99]

I figured this would be a good winter project while I am convalescing. I need to make a couple of battery boxes. One that will hold three 6V batteries and another that will hold one 6v battery. You may ask, why not just buy them ? Well I would, but at least for the 3 battery box it will not fit. The bulbous top of the plastic ones is just to tall. I have also not found one that would hold 3 batteries and fit into the space I have. So I thought about making them out of plywood and either just epoxy coating all the wood or covering the wood with a layer of fiberglass and epoxy, which I happen to have left over from another project.

I also have "normal" plywood in either 1/4 or 1/2 inch thick size drops. I even have a few pieces of 3/4 plywood.
So I am looking for a little help from the great minds of sailnet. I have a lot of questions. Where should the cables enter and come out ? How many vents and where should I put them ? Should the lid, be a drop in type, or one with a lip that sits on top of the box ? Make the battery hold downs out of what ? So what do you people think ?

Thanks,
Paul

[chucklesR]

Paul,
Frankly those of us that do this type of building don't know enough to help, except in a general way.
1/2 ply would do and be easier to work than 1/4 (not much surface for screws/nails). I suggest epoxy and a layer of glass both inside and out for protection and strength.
As to where to put the cable openings, where do they fit best and lead to the batteries with the least amount of contortions? Normally the top - thru a hole (a U shaped opening under the lid - not thru the lid) - You'll want a rubber grommet on it for chafe protection.
Strap downs depend of course of battery type and weight - if wet cell, acid proof strapping, if AGM, normal tie down strapping suitable for the weight of the battery - personnally I prefer both fore and aft strap downs. Most prebuilt boxes only put in one strap which seems dangerous to me.
Venting also depends on battery type.
As to the lid being a shoe box or or sit on top - shoe box adds more form stability as well as tie down/clamp down options (it would also nicely close off the top of the 'u' channel for the cabling).
Why 3 and 1 as opposed to two x two? Space availability? Think AGM's and you can open up the possibilities as they can be stored sideways, upside down etc..

[Freesail99]

The battery are wet cell golf cart batteries. The 3 and one boxes are because that is where I have space. Actually, the one box is really 2 boxes as it would also be where the 12v starter battery would be located. That location is the bottom of the wet hanging locker, under the bottom shelve. I had though to use some garden water hose as chafe protection.

[thekeip]

To codify the ABYC's feelings on the subject: the box should contain the batteries with no more than 1" movement in any direction. Note that this includes vertical movement; however, it's not strictly necessary to cover the batteries with a lid (but if you do, the lid can't entrap gasses given off as a result of charging). What this says is that in the event your boat capsizes, your batteries need to be restrained. Also, your battery box needs to be able to contain whatever liquid(s) might be sloshing around. Many owners use heavy duty nylon web for the hold-down but remember, batteries are HEAVY...seeming more so if they're upside down.
How the cables are routed is up to you...no spec from ABYC specifically re routing...except no spring clamps (like on portable battery chargers) are allowed.

Howard Keiper
Sea Quest
Berkeley

I've got the standards at my boat but this is usually good enough to satisfy a survey. If I find anything else I'll post it to you.
Howard Keiper

[soulesailor]

I built a custom wooden box for my 4 6v golf cart batteries out of 3/4" plywood and solid IPE pieces. I built the base out of ply with 1x4 IPE pieces through screwed from below to divide the base into individual battery holders. I made this grid with nearly zero tolerance so the batteries are immovable in two dimensions. I put plywood sides on and screwed the whole box into the nearby plywood of the structural furniture. Then I put wooden cleats all around the top and made a plywood top which screws into these cleats, also with nearly zero tolerance, to lock the batteries into the box in every direction. In addition to screws I glued everything with Gorilla glue (except the top which has to be removable). My venting and cables come through the sides where it attaches to the boat's structural ply. I used #10 self tapping SS screws everywhere. It would take a tornado to shake these things loose. I wouldn't use 1/4" or 1/2" ply, nor would I screw into the end grain of the ply (that's where the cleating comes in). I didn't glass anything in. Maybe this is a good idea but I spent so much time on this project I was ready to move on and so I skipped any glassing.

[jasonr575]

I had a leaking battery last year that got the bottem of a bulkhead wet and started to soften the wood. Did some reasearch and found that west systems epoxie is acid resistant. (spoke to the company). Use that to coat the inside of the box. Several 1 in holes drilled in it should provide enough venting and it should be obvious where you should put them and the wire opening. Should go wherever convenient. use nylon webbing for the hold downs like you get with the boxes at the store.

[CapnHand]

Batteries tend to bulge over time. This is normal due to the weight of the acid inside and the plastic that the battery case is made from. For this reason, making the box "zero tolerance" may not be best. If you do, over time you may find that the batteries have become stuck in the battery box.

[soulesailor]

Yes, the batteries do bulge over time. I should clarify my box design. The tolerance isn't quite zero and is only the bottom 3 1/2" (I used 1x4). Then the next piece that locks the batteries in is a thin (maybe 1 1/4") cleat at the top and the plywood top itself. The majority of the battery's sides are 3/4" away from the plywood. I did have to put nylon webbing under each battery because getting them out of a box only 3 1/2" tall is still tough.

[Freesail99]

Did the cleats on the top interfere with the removal or placement of the batteries ? I had planned on using 3/4 for the bottom of the box. If I screw into the end grain, I plan on also using epoxy as the "glue" so my screws are really holding things in place until the epoxy drys. The fiberglass and epoxy of the entire box would add a huge amount of strength.

[sailingdog]

I would fiberglass and epoxy both the interiors an exteriors of the boxes. This will help protect the wood from the acid and from damage caused by spilled water, etc...

Use the 1/2" ply for the boxes, and join them using a thickened epoxy fillets. Might want to use 3/4" ply for the base of the 3-battery box.

Put cleats inside the box to center the batteries and prevent them from shifting side-to-side or fore-to-aft.

I'd make the tops out of 1/4" ply, with a center section of 1/4" ply laminated to it, so that it sits centered on the battery box. The cable cuts in the box should be u-shaped at the top and will work both as cable entry points and vents. Hinge one side and then put a padlock hasp on the opening side to secure the lid.

The battery hold downs can either be straps or a solid wood cross brace. Personally, I like the wooden cross brace better. Or, you could use the lid as the hold down for the batteries... if you hinge it and put cleats on the underside positioned to secure the batteries when it is shut. If you use the lid to secure the batteries, you'll probably want to go up to 1/2" ply for it.

If you make the base plate of the box a little wider or longer than the outer dimensions of the box needed to hold the batteries, the extra flange on either side can be used to bolt the box in place, or if the box has to fit back into a storage area, you could use rails to hold the flanges down... and it would allow you to slide the box in and out for easier servicing.