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Re: (ET) Fully charged pack voltage
It's important to make the distinction between open-circuit voltage
(resting
voltage, with nothing connected, 12 to 14 hours after the charge has been
stopped) and on-charge voltage (the voltage with the charger connected).
When you read that a battery should be charged to around 2.4 to 2.5 volts
per cell, that is the on-charge voltage.
However, that by itself is NOT enough information! A battery isn't
charged
until it reaches the specified voltage AND the charge current has fallen
to
about 2% of the battery's 20-hour amp-hour capacity, expressed in amps.
For example, you should charge a 240 amp-hour golf car battery until its
on-
charge voltage reaches around 7.35 volts (some say as much as 7.5 volts)
and
the current falls to 4.8 amps.
Another strategy is to charge the battery until it reaches some
empirically
derived threshold voltage, such as 2.3 or 2.4 volts per cell, then hold
the
current at about 2% of capacity until the voltage effectively stops rising
(dv/dt charging). This is what Lestronic golf car chargers do, though
some
of them keep the finish current too high (IMO), around 8 amps.
I suggest reading this document :
http://www.evdl.org/pages/hartcharge.html
Open-circuit voltage is an inaccurate indicator of state of charge, but
it's
all you have for sealed batteries. If you're using flooded batteries,
there's no reason to use voltage, because a hydrometer is much more
accurate.
http://www.evdl.org/pages/socvolts.html
PS - I say again : in my experience, more batteries die from overcharging
than from undercharging.
David Roden - Akron, Ohio, USA
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