No experience with those batteries myself but
http://www.dcbattery.com/agmtech.html, for example, specifically says "AGM
(Absorption Glass Mat) technology batteries can be charged at normal
lead-acid regulated charging voltages, therefore, it is not necessary to
recalibrate charging systems or purchase special chargers."
But this link - http://listproc.ucdavis.edu/archives/cbx/log0408/0093.html -
does advise some caution.
Lots of other links at
http://www.google.co.uk/search?hl=en&q=glass+mat+battery&btnG=Google+Search&;
meta= ("A wonderful thing is a Google, a Google is a wonderful thing ...")
See also below.
PaulH.
----- Original Message -----
From: "James Nazarian" <jhn3@uakron.edu>
To: "mgs" <mgs@Autox.Team.Net>
Sent: Saturday, January 15, 2005 3:08 AM
Subject: OT battery question
> 1. The guy that sold it to me said you can't use a standard battery
charger
> on it but that I should use a run of the mill 12V 1A wall transformer as a
> charger is that true? Why?
Dunno why that would be, volts is volts and amps is amps. If it needs a
special charger it is more likely to be one with a special charging profile
that varies amps/volts according to the charge in the battery, a bit like
those conditioning chargers you can leave connected to a lead-acid (at
least) battery all the time. But a '12v 1A *transformer*' says to me 'AC
output' which surely isn't right to charge a battery. Maybe he means a 12v
charger with a 1A maximum output current.
> 2. What is to keep it from overcharging or boiling the battery?
Exactly! If the battery can only have a maximum charging current then there
must be electronics in the charger to control the current and/or voltage, or
the transformer must produce a maximum output voltage at a level that cannot
deliver more than 1 amp even if the battery is completely flat. But as the
battery charges that would gradually reduce the current, and hence the
charging rate, which could take a long time to fully charge. On a
conventional charger the current is dependent upon the amount of charge left
in the battery and hence its voltage, as well as the voltage applied by the
charger, up to the limit of what the charger can physically supply. Put a
flat battery on a big charger with a high voltage output and you well get a
high initial current and a relatively short charge time. As the charge in
the battery builds the voltage rises, which because that reduces the voltage
differential between battery and charger reduces the current flowing. Put
the same flat battery on a charger where the transformer limits the output
voltage to about 14v and you will get the same sort of charging current you
get on-car.
> 3. If the battery is 7Ah and the charger is 1A will it take 7 hours to
> charge the battery?
>
For a lead-acid, for example, all else being equal charging time depends on
the charge left in the battery to begin with, at a constant current it will
take less time to fully charge a 25% discharged .
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