Padu,

It sounds like you might want to look into what RV and long haul
truckers have set up for their dual battery situations.  In them there
are two batteries - one to start the engine and one to run accessories.
They are both charged IRC from the same alternator.  Sounds like your
problem is actually well known and solved in those industries.

Hope that helps.

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Metis Adrastea
> Sent: Thursday, March 16, 2006 3:04 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Basic question on auto batteries
> 
> Hi!
> 
> 2006/3/16, Padu <padu@merlotti.com>:
> > Hi,
> >
> > For my autonomous ATV project, I will have two automotive batteries
> onboard and a automotive alternator generating up to 90A @12-14V. The
> motors I will use the automate the ATV systems (steering, brakes, etc)
> work at 12 or 24V. My dillema is: how to connect the batteries, series
or
> parallel?
> > In series I will have more punch for the motors at 24V, but how do I
> charge them using the 12V alternator? Can I use diodes to somehow
direct
> the current to charge both batteries at the same at 12V but get 24V
out of
> both? The motor manufacturer said the motors will work at 12V (at half
the
> speed of course) and torque will be the same, since in his words,
torque
> is not related to voltage, but to current.
> > As the motor was originally designed for 24V, I prefer going that
route,
> but not at the cost of complicating my design on how to charge the
> batteries... do you have any suggestion?
> 
> Probably opening the bridge between the two batteries with a relay
> (contactor) during charge?
> 
> Regards
> 
> Metis Adrastea
> --
> 
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> 
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