Tuesday, March 24, 2009

Battery Box

Here is the battery box I built, with 3 - 12v marine batteries each 105 amp hours.
An amp hour means you can run something that draws 1 amp (or 12 watts) for an hour.
I will have 315 amp hours in my system, so if I wanted to know how much energy I was using to run a 60 watt lightbulb on my 12v power system, it would use 5 amps in an hour, or 5 amp-hours. If I wanted to use a 500 watt heater, it would use 41.6 amps per hour. (500 watts divided by 12 volts) So I could only run my heater for about 6 hours before my batteries were dangerously low.
Amps X Volts = Watts
so Watts divided by volts equals amps.

I highly recommend the 'Boatowner's Mechanical and Electrical Manual' by Nigel Caulder. It is not a cheap book, but if you own or are building a boat, RV, or Freedom Van it is a great investment. It has detailed information and drawings, diagrams and pictures on all critical systems; 12volt and 120 volt electrical systems, solar panels and wind generators, propane heating and refrigeration systems, plumbing, troubleshooting, and diesel engine repair, among others.

They can explain all this better than I can.

My batteries will be connected in parallel, with the positive terinal of one connected to the positive terminal of the next, and negative to negative.
This will give me 315 amp hours at 12 volts.
There will be a positive cable attached to the van's starting batteries, and running through a battery shut off switch to the positive terminal at one end of my 'house bank' of batteries.

Cheap Battery shut off switch from Harbor Freight
(the nice ones are $50.00 at West Marine, this was $5.00. Hope it doesn't burn shit down.)

This will let me charge the house bank with my alternator when the switch is on, and turn the switch off when I quit running to avoid draining my starting batteries while I run lights or heat up water in my hot pot. All interior lighting and electrical (inverter) will be run from the house bank.
The house bank will also be backup power to help the van start if for some reason the starting batteries should die. Just turn the battery switch on, and crank 'er up. (as long as I didn't leave my heater on all night, then I'd be SOL.)

The battery shut off switch, inverter and terminal strip will be mounted to the sides of the battery box, aft of the seats. My drink holder gets mounted to the front of it! :)
I don't have the top on yet, but it will be hinged on the forward side so it opens to the aft, so I can maintain the batteries or add electrical components. There will be another smaller box on top that will double as a seat and center console compartment that opens toward the front. I've got to have someplace to keep maps!

Time is running out. I probably won't get a chance to mount the solar panels for my back up charging system, but I will take them with me. Maybe I can do it in Washington (for all the good they'll do up there).

I'd better get back to framing up the kitchen....


  1. Do those batteries have to be vented? Don't want gases to build up in the box. Of course, I'm using flooded lead acid types. Some batteries don't outgas.

    Impressed with the general level of workmanship. Tough to do when racing the clock, as you seem to be.


  2. You are correct Sixbears. Flooded lead-acid batteries give off explosive hydrogen while charging. Venting is not necessary for 'maintenance free' sealed batteries.
    These are flooded, and when I run the wiring I will drill holes for the vents.
    I want an intake on the bottom of the box, and I'll install a hose barb toward the top for the exit since hydrogen is lighter than air.
    I'm still working out how I'm going to vent it to the outside; I'd rather not make more holes in the van than necessary. Ideally, I'd be able to collect the H and use it for something, but I'll cross that bridge when I come to it.
    Thanks for asking that question, I meant to include venting in this post, but it started to get really long and I forgot.
    I figured I could cover it in the electrical post once I get things wired up and take pictures...