Date:         Mon, 27 Mar 2006 13:58:46 -0700
Reply-To:     Richard A Jones <jones@COLORADO.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Richard A Jones <jones@COLORADO.EDU>
Subject:      Re: charge rate at main & aux batt
Comments: To: trclark@SHAW.CA
Content-Type: text/plain; charset=ISO-8859-1

> now i have a 2 question i would like confirmed
> Is an over charge condition to a battery only when the voltage supplied by
> the alternator is HIGHER than
> the voltaged required by the battery during re-charge
>
> Is an under charge condition to a battery only when the voltage supplied by
> the alternator is LOWER than
> the voltaged required by the battery during re-charge

This is basically correct.  Every battery has a specified charge
voltage, adjusted for temperature.  If you charge with a smaller
voltage, the battery will not fully charge.  Larger voltage and
the battery will start to gas after being fully charged.  Here
is some more info on charge voltage vs temp:
http://www.trojanbattery.com/Tech-Support/BatteryMaintenance/Charging.aspx
See point 6.  Also, note that Trojan specifies higher charging
voltages than some other batteries; not all flooded batteries
are the same.  Most specify 14.4 volts at 80 degrees.

How do I know this?  Because I help take care of a photovoltaic
light system at a cabin at 10,500' in the mtns behind Boulder.
The batteries (4 Trojans) drop to about 15 F degrees in early
December.  Now they are about 35 degrees.  The cabin is used really
only on Saturday and Sunday, so there is no way to keep the batteries
warm.  We have to raise the charge level of the charge controller to
its max (15.3 V) to get the batteries fully or almost fully
charged.  Now as it warms up, we need to decrease it.  That is
the advantage of a temperature compensated charge controller.  I
with my screwdriver am the temperature compensator for now.  ;-)

                                Richard A Jones
                                Boulder, Colorado