DIY vented battery box - what to use?

[olsen_karl]

I'm going to install two 6V golf cart batteries in my truck camper, as the 12V battery it came with is marginal. The 12V battery is inside a cabinet inside the camper, and vented to the exterior in a box like this one:
http://tweetys.com/largeboxcolonialwhiteandventkit.aspx

The battery box has a drain hole through the floor, plus the flex hose vent out the top, which leads to an exterior vent on the camper. It has a screw-on lid, which is an annoyance when I want to open that box and directly connect a battery charger. I have enough cabinet space to fit two large batteries, easily.

To go from the single battery to a 2-battery 6V system, I either need to use two of these vented boxes, or one bigger box. The only retail vented boxes I've found that are large enough to hold two golf cart batteries are overpriced, at $80-90ish, and don't have a vented hose out the top. I think these are intended for marine or exterior mounting, not inside an RV.
http://www.tank-depot.com/productdetails.aspx?part=PRO-4021

Anyone built their own interior battery box for 2 largish batteries, with a vent to the exterior? My thought is to use a sturdy plastic storage box from Target, Home Depot, etc. -- something with a mechanical clip-on lid, for easier access to the batteries.

Something like this:

But with mechanical clips over the top to hold the lid on, like an Action Packer:
http://www.amazon.com/gp/product/te...=AKIAJKV3RDOEW4KWVUPQ&creativeASIN=B00002N9F9

I just need to figure out the top and bottom vents for the plastic box. Am I correct in that the bottom vent is necessary? (for chimney air flow-through, to assist any hydrogen off-gassing in venting out the top vent?)

 

[dwh]

There is a formula for figuring out how much hydrogen batteries generate. Lemme see if I can find it...

Yea, here:

http://giantbatteryco.com/GLOSSARY/Calculate.Industrial.Battery.Hydrogen.Gas.Emission.html


They say, "motive power battery" - that's pretty much what a golf cart battery is. Their example shows a 24 cell 450ah bank generates about 8 cu.' of hydrogen per hour of charging. Your two 6v golf cart batteries will have a total of 6 cells (so that's 25% of what they used in their example), and also a pair of 6v 225ah batteries rigged in series to get 12v will be a 225ah bank (which is half of the number they used).

So a decent WAG would be about 1 cu.' of hydrogen per hour (of charging) for a pair of 6v 225ah batteries.

A 2" hose would likely be enough to allow that much to escape - even without a fan or intake duct. It'll just rise through the column of air in the hose...sort of like bubbles in a glass of beer rising to the top.


A drain in the bottom is also a good idea, even if you don't need it as an air intake. You'll have to add water to those batteries once in a while, and you might spill some. There also might be some normal battery surface corrosion which you might want to wash off now and again.


Personally, I would use an intake vent anyway, and the drain can serve double duty by also being the intake.

There is a drawback if the intake draws air from outside; When it's cold out, the vent system will do a nice job of cooling the batteries, which isn't great since batteries don't work as well when they are cold. YMMV.

 

[olsen_karl]

Thanks dwh - helpful information.

The drain in the bottom of my existing battery box is a small (~ 1/2") hole, bored through the bottom of the camper, somewhat in the middle of the camper. It would "drain" straight onto the rubber bed mat in the truck bed.

I'll take some measurements on whatever plastic boxes I can find at Walmart, Home Depot, etc., and see what looks promising. I think I can either cut out and re-use the top vent on the existing battery box, or perhaps use some sort of PVC flange. I don't think this needs to be a perfect, airtight setup.

 

[Tony LEE]

Lots of setups use two holes but both go out through the bottom. One in one corner is just a hole in the bottom. Second one in the opposite corner has a tube that comes through the bottom and extends up close to the top cover.

 

[olsen_karl]

Lots of setups use two holes but both go out through the bottom. One in one corner is just a hole in the bottom. Second one in the opposite corner has a tube that comes through the bottom and extends up close to the top cover.

I think I'll run a vent out the top -- hydrogen is lighter than air, so I'll help it evacuate out the top, through the existing hose and vent to the exterior of the camper.

 

[AxeAngel]

Any reason you decided not to go with sealed batteries?

-Sam

 

[olsen_karl]

Any reason you decided not to go with sealed batteries?

-Sam

Cost.

6V golf cart battery is ~$90 each at local Costco, standard lead-acid type battery.

A 6V AGM golf cart battery looks like it will be well over $200 each.

 

[olsen_karl]

I finished this part of my camper project today, so at least the battery box is in, and the batteries installed and connected.

I used a copy of an action packer from Walmart, as the internal size was nearly perfect for fitting 2 golf cart batteries, with almost 1 1/3" clearance above the terminals. The batteries fit snugly inside the box and do not have enough space to tip over, or even move sideways much at all. The box is gray/tan with a green lid, and IIRC, 10gal size. It has hinges on one side, and a click-shut latch on the other; the lid is fully removable. I cut away part of the hinges to make it a little easier to remove the lid.

I decided not to mount the box to the floor of the camper, but rather screwed a tie-down strap to the floor in two places, underneath the box. The strap then wraps around the box and cinches over the lid. It holds pretty well. This way, I can move the box around as needed, in order to open the lid and connect an external battery charger, and also to add water to the batteries.

I made the top vent for the box out of some plumbing supplies from Home Depot; cut a hole in the lid with a hole saw, and sealed around the vent tube with RTV silicone. I reused the existing vent tubing, which exhausts to the sidewall of the truck camper, near the truck cab. I didn't do a floor vent -- after doing some more internet searching, it seems that many RV battery setups don't use a bottom/floor vent, but only a top vent (some don't use any vents, but that seems quite risky).

I'm pretty happy with the way it turned out. Thanks again for all the assistance with this project -- this forum is a great resource.

I'm partway through the rest of the project, which is to wire the camper 7-pin harness to the truck battery, so it charges while driving. I had to stop as I ran out of split loom, but nearly everything else is done.

 

[kjp1969]

I'd suggest bolting the batteries down to keep them from flying around in an accident. Use the plastic box that you have, drill down on either side of the batteries and use 3/8" all thread and some stout bar stock to keep things in place. Done properly you can still access the batteries from the top by removing the plastic lid, but that lid isn't trying to restrain the batteries.