Nothing sucks worse than being stuck out
in the middle of nowhere with a dead battery in a jeep with an auto
tranny. I've added a welder, onboard air, and extra gas cans to my
CJ-7 to increase my survival odds in the wilderness, but if my
battery dies it's all useless. A dual battery system, when properly
set up, can greatly decrease your odds of ever being stranded with a
dead battery.
There are lots of
nice dual battery systems available for purchase out there, but
buying stuff is no fun when you can make it...especially if it saves
you a large chunk of change. A couple years ago, the discussion of
dual battery systems came up on the off-road.com short wheelbase
Jeep BBS and out of that discussion was one of the best home brewed
dual battery systems I've seen to date. It was designed by CJDave
and TeamRush (whom also designed the Duraspark TFI upgrade).
The great thing about the system is it's simplicity while still providing the options you would want in a dual battery system.
One of the great additions that CJDave made to TeamRush's initial design is to add an oil pressure switch to the circuit. The batteries remain isolated until the oil pressure
switch is opened. This will happen when your oil pressure reaches a certain PSI...and
this can only happen when your engine is running. This only allows
both batteries to be used when the alternator is able to charge them
both (engine running). The second battery remains isolated and in
reserve for self jump-starts as long as the engine is not running. A
momentary self start override switch is also in the circuit. This
will bypass the oil pressure switch and allow both batteries to be connected so you can essentially jump-start yourself if your main battery is dead.
Surprisingly few parts are needed for this
system, which makes it fairly cheap (as far as dual battery systems go). Here's a diagram of the system:
The only parts needed (not including the second battery and tray) are a continuous hold solenoid, a Hobbs oil pressure switch, a momentary switch, and some 2/0 fine welding cable.
I decided to start this project out by first designing and building my dual battery tray. I went to my local steel supplier and dug through
their remnants until I had enough material to build the tray.
If you don't have the option to build one, here's a nicely built one to buy:
My battery tray is a
bit overbuilt, but I was using what I could get cheaply from the
scrap bin and there isn't that much weight difference with this
small item anyway. Here's the basic materials and design of my
battery tray.
This project is not yet complete. Check back for the complete write-up with
photos.
