> -----Original Message-----
> From: tclug-list-bounces at mn-linux.org
> [mailto:tclug-list-bounces at mn-linux.org]On Behalf Of Donovan Niesen
> Sent: Thursday, February 01, 2007 12:13 PM
>
> I'm considering a project that would involve connecting a very
> low-power Computer on Module and an LCD display inside a vehicle.  The
> vehicle will not be driven or possibly even started for an entire week
> so what I'm wondering is if anyone knows how long I might have on a
> fairly standard car battery if I'm using ~35 Watts from the LCD and
> the CoM?
>
> My goal is a full 7 days so if I need to use a lower power LCD so be
> it.  Otherwise I will need to find a different way to power the
> device.
>
> And yes, the CoM will be running Linux.
>

You should be able to extend the battery life by using power cutback
routines in both monitor and computer thingy.

Still, it's never a good idea to risk that the car won't start.  Better
to use a second battery that can go dead and not affect car starting at
all.  This is a standard RV setup: use two fat power diodes from the
alternator (common anodes) and separately to each battery.  Leave the
car wiring the same otherwise.  Whichever battery most needs charging
will get charged and both will be OK.  The auxilliary battery can go
dead and the car will still start.  I found that it was cheaper to use
guaranteed KMart batteries and not the expensive deep-discharge
batteries because they will die in about the same time and the guarantee
will usually replace for free or cheap.  A regular car battery needs to
"see" starting current now and then to keep its pores open, and that
would need a bit more to automate swapping the battery roles.


Chuck