Date:         Wed, 28 Mar 2007 01:34:55 -0500
Reply-To:     Matt Roberds <mattroberds@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Matt Roberds <mattroberds@COX.NET>
Subject:      Re: Trickle charging battery with 1.8W solar panel = failure
Comments: cc: Martin Jagersand <jag@CS.UALBERTA.CA>
In-Reply-To:  <20070328022348.WZOO9199.fed1rmmtai101.cox.net@fed1rmimpi03.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

> From:    Martin Jagersand <jag@CS.UALBERTA.CA>
> Date:    Tue, 27 Mar 2007 17:57:03 -0600
>
> I haven't measured the parasite load on the battery recently. Should
> only be the clock, so no more than a mA or so.

You might check it.  Car starting batteries don't usually have an Ah
rating, but if they did, it'd be somewhere around 40-50 Ah or so.  1 mA
for 5 months is 3.6 Ah, or less than 10% of the battery capacity... not
too bad.  But 5 mA for 5 months is 18 Ah - over a third of the battery
capacity and approaching half of it.

> Maybe internal discharge increases with time?

In my experience, this is true.  Older batteries tend to self-discharge
faster.

For way more than you ever wanted to know about it, read this FAQ:
http://www.uuhome.de/william.darden/carfaq.htm

matt Roberds