Date:         Wed, 21 Apr 2010 10:28:17 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: charging aux battery: too much of a good thing?
Comments: To: Alistair Bell <albell@SHAW.CA>
In-Reply-To:  <4999475E-E31D-414B-9869-288C02AB62C4@shaw.ca>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 09:34 PM 4/20/2010, Alistair Bell wrote:
>As for rate of charge, correct me if I am mistaken but if voltage
>fixed, then current is self limiting. I have a hard copy of a very

With fixed voltage, charge current is limited by the lesser of supply
capacity or the acceptance of the battery.  With a discharged battery
acceptance is very high -- a three-stage regulator will charge at
full alternator output until a specific voltage is achieved, then
hold that voltage while the battery acceptance declines toward zero,
then reduce the voltage below gassing levels.  An automotive
regulator OTOH will simply reduce output as the battery voltage rises
toward the regulator set point, eventually getting to zero output
when the set point is reached.  This is perfectly adequate for
replenishing a starting battery which only loses a few per cent of
charge in starting; but for a house battery that is deep-cycle it's
an extremely inefficient way to do it.

Yrs,
d