[Oeva-list] AGM battery charging question (Tim Kutscha)

[gfifield at onlinenw.com]

Too bad there isn't a pressure sensor built into each cell to reveal when
this condition is starting. Then the charging voltage could be dropped to
float value. Does anybody know if the pressure relief mechanism could be
used to detect each burp of gas?

Gene
 > Tim,
> My understanding is over charging does not just turn into heat it causes
> the
> battery to make Hydrogen and in AGM can over pressurize the battery.  If
> the
> gas vents some of the precious electrolyte is lost forever.  Dropping from
> the constant voltage part of the charging to the lower float voltage or
> just
> ending the charge cycle with no float voltage is important for longest
> life.
> Sounds like you are going for 100% charge. That is the thing to do if
> maximum range is your goal.  If you are looking for maximum battery life
> only charging to 90% and never discharging below 40% appears to double
> battery life.  Everything has tradeoffs
> David Kerzel
> -----Original Message-----
> Message: 1
> Date: Thu, 25 Jun 2009 17:52:51 -0700 (PDT)
> From: Tim Kutscha <tim_kutscha at yahoo.com>
> Subject: [Oeva-list] AGM battery charging question
> To: oeva-list at oeva.org
> Message-ID: <307234.97758.qm at web110510.mail.gq1.yahoo.com>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi all,
>
> I've got a technical question about AGM batteries for you battery experts
> out there.  A typical smart charging system will dump current into an  AGM
> battery up to a critical point (say 14.4 volts at 25 degrees C) and then
> hold that voltage until the current drops down to, say, 1 amp before
> dropping to a float voltage (like 13.6 volts).  My question is:  if the
> current going into the battery drops to around 1 amp, how long can I
> safely
> hold that 14.4 volts before hurting an AGM battery?  I would think that
> the
> current going in is so small, it would just be dissipated as waste heat.
> I'm using 100Ahr Concorde Lifeline AGM batteries.  I have resistive shunt
> balancers on all the batteries for balancing that kick in around 14.4
> volts
> depending on the ambient temperature.
>
> Any thoughts?
>
> Cheers,
> Tim
>
>
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