Date: Fri, 2 Feb 2001 09:22:51 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Battery question
In-Reply-To: <007d01c08d10$4f35e860$104e2526@net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Optima's FAQ says that problems are unlikely in automotive use at less than
15v alternator output. They say for continuous trickle chargers not to
exceed 13.8v or one amp.
That being said, you have to ask yourself what you want it for, and how
dedicated you're willing to be vs what results you require. If you want
full capacity and maximum life, it is going to require several things, to
wit: 1) a smart 3-stage regulator that knows enough to turn the max voltage
down when your headlights are on, to avoid burning out the halogen bulbs --
and that monitors battery temp while charging. 2) A monitoring system that
can work the Peukert equations in real time i.e. at least 100 or so times
per second. 3) some care and thoughtful attention to what's going on. 4)
sizing your installation so that your amp-hour capacity is equal to the
greater of roughly 4x your daily usage or 3-4x your maximum instantaneous
consumption, and 5) keeping your batteries above 50% charge, after 6)
breaking them in properly with several C/10 discharges down to ten volts or
so, with proper full charges in between. And -- oh yeah -- an alternator
that can handle continuous charging at full output.
That means at least $600 in regulator and monitoring gear, plus a few
hundred for a hot-rated alternator if necessary, plus paying
attention. But the battery will likely last ten years. You can run it
down to 25% and lose noticeable life, or you can run it flat and lose lots
of life.
If you can't spring for the monitoring gear, you have two choices: 1) Use
two banks alternately, and measure voltage under zero load after a bank has
sat unused for 24 hours to determine state of charge, or 2) forego knowing
what's left in the can and when you ought to recharge. The smart regulator
will still charge fully, so you'll lose cycle life but not battery capacity.
If you aren't willing to spend $300 on the regulator, you must resign
yourself to running chronically undercharged which will permanently reduce
the battery capacity. The voltage necessary to fully charge these puppies
(about 14.7 adjusted for temperature) is absolutely incompatible with
keeping them around for long after they're charged, so the dumb automotive
regulator will simply undercharge them, and slowly to boot. This is
irrelevant for a starting battery where you only use a couple per cent of
charge per start, but a big deal for deep-cycle batteries.
The main competitors I know of for fancy regulators are Cruising Power for
$200 and Ample Power for $300 -- maybe also Ballmer for $200. The Ample
Power guy and the Cruising Power guy have been fighting for fifteen years
now -- I personally believe that the Ample Power guy has it
right. http://www.cruisingpower.com/ (I tink), http://www.amplepower.com/
. More than you want to know at the latter site. I have his cheap ($300)
regulator on Scamp and it behaves exactly as advertised (but no monitoring
gear. I do have two banks so I can do voltage checks on the inactive
one. I'm using flooded-cell deep-cycle batteries on both banks -- I can
use them for starting b/c the Atomic 4 cranks very easily, especially at
age 38!
http://www.powertap.com/ in Seattle is hand in glove with Ample Power --
they sell the gear and also have alternators etc.
david
At 07:04 AM 2/2/2001, Jonc wrote:
>A techy at Boats US told me that if an Optima battery is charged at over
>13.8 volts for 90 days it is toast... I do not know where he got his info
>but he believes it and sells a lot of Optima batteries... he is recommending
>some sort of voltage reducer from radio shack or the high price spread
>custom voltage regulators ... his real advice was not to buy an optima
>unless you are prepared to check the voltage regularly and will dampen down
>alternator charge rates to 13.8
>
>Does anyone have the skinny on this?
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
