Bill Pitz <bill@pitz.net> wrote:
> I've been thinking about a multiple battery setup for a while... figured
> I'd post here first to see if anyone has already thought up a good way
> to do this.
> I'd like to add a second battery to my truck -- something more suited
> for deep cycle use. The idea would be to have a power source to use for
> the stereo, light air compressor use (for tire inflation), etc. when
> camping and such.
> In a perfect world, I'd like to have the starting battery completely
> disconnected from the vehicle's electrical system when the truck is off
> (a manual switch that I could activate when parked at the campsite would
> be fine, too). Both the deep cycle and the starting battery should be
> able to charge off of the truck's alternator when the engine is running.
> I know I need a battery isolator to accomplish this -- but what about
> the switch between starting/deep cycle once stopped?
A battery isolator would definitely be a good idea in this case,
where you will have your main battery which will remain at full charge
and the deep cycle which could potentially be drained low. If the
batteries were wired in parallel and a switch or solenoid were used to
simply disconnect the main battery while the deep cycle were used,
upon reconnection, the main battery will try to "charge" the deep
cycle, and depending on the voltage difference, this could result in a
large current surge, which could potentially drop your main battery
down low enough to have trouble starting the vehicle, and will
definitely reduce the life of both batteries.
One possible method which comes to mind would be to use a battery
disconnect and a battery cutoff switch. The negative battery terminal
on the deep cycle battery is connected to ground, the output from the
alternator would run to the battery isolator, which would run to the
positive terminals on both batteries. You can put a battery
disconnect on the negative terminal of your main battery (something
like this: http://tinyurl.com/262pjn). You would then run a wire (of
the appropriate gauge for the accessories you want to have running at
the campsite) between the positive terminals of both batteries, and
install a battery cutoff switch in that line between them (something
like this: http://tinyurl.com/2wv228) Or, you could use a battery
disconnect here as well (on the positive terminal of the deep cycle),
as long as you make sure that the line from the battery isolator to
the positive terminal on the deep cycle is on the side of the
disconnect which is always connected to the battery.
How you would use the above is under normal circumstances, the
battery disconnect on the negative terminal of the main battery is on
(connected), and the battery cutoff switch between the two batteries is
off (disconnected). This will allow the alternator to charge both
batteries while still having them isolated from each other. (The deep
cycle battery is also isolated from the vehicle; the ground is always
connected, but the switch between the deep cycle and the
regular battery is off.) Once you get to the campsite, you would
turn on the switch in the line that runs between the two batteries and
then turn off the battery disconnect on the negative battery terminal
of the main battery. (You can do it in the reverse order also, but
this way your radio presets and such are saved. Basically what this
is doing is to briefly wire the two batteries in parallel. This
shouldn't be a problem though as far as a current surge goes because
both batteries should be charged to the same voltage.) Naturally,
you just reverse the procedure when its time to leave the campsite.
(Though in this case it might be safer to turn off the switch between
the two batteries before reconnecting the negative battery terminal
disconnect, since at this point the batteries are at different
levels. You can always get one of those thingies which plugs into
your cigarette lighter and has a 9v battery to maintain your presets
for the few seconds while you flip the switches.)
The above is certainly one way to go, its not automatic, you do need
to flip a couple of switches, but it'd be pretty cheap, you'd just
need to buy the wire, a battery cutoff switch ($5) and a battery
disconnect ($2-5). The isolator will probably be $50 but you need
that anyway. (Hmmm, looks like Northern Tool has a 90 amp isolator
for $25 which seems like a really good price.) A possible variation on
the above might be to use a large diode (which is really what the
battery isolator is) in place of the switch between the two batteries.
This would allow the deep cycle to provide power to the vehicle at all
times while preventing the main battery from "charging" the deep cycle
back through that line. Under that scenario, all it would take to go
from normal to campground mode would be to turn the knob on the
disconnect on your main battery. Your radio station presets and such
would be saved also. You'd just have to remember to disconnect the
deep cycle battery when you want to remove power to the vehicle prior
to doing maintenance, etc.
I've never done the exact setup described above so YMMV; if
somebody spots a problem with this, please speak up, but as far as I
know this should work for what you want.
> I'm also curious where others who may have done this have put the
> additional battery and the isolator. I'd like to avoid losing any space
> in the bed if possible.
I can't really help as far as the Dak goes, I added secondary
batteries to my Ram which I put under the hood, you might not have
room for that. I also added a secondary battery to my Jeep which I
put in a center console, but it is an open air vehicle, you shouldn't
install a battery in the cab of your Dak. :-) If you go with an
Optima style (gell) battery, that can open up some more opportunities
for you since you can mount it in weird positions. I have heard of
several people mounting them under the bed; if you have access to a
welder this may be an option for you.
Good luck!
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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