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Preparing
the batteries:
The
Electric Imp's development battery pack is made up of 180 2.14 volt
25 amp/hr Cyclon
BC batteries. These batteries will be wired in series, meaning
the negative of the first battery will be connected to the positive
of the second battery. The voltages are added 2.14 volts + 2.14
volts. The end result is a 385 volt, 25 amp/hr pack.
These
180 batteries were not made at the same time and have seen different
usage. This means they have aged differently and no longer have
identical capacities. This is not the optimum set up for a battery
pack. It is fine for testing software and charging methods. It is
a pack we can make mistakes on.
When
charging batteries in series, it is best to start with all the batteries
at the same state of charge. Otherwise, some batteries will reach
full charge and start to overcharge, while others in the series
will not yet be full. The simplest method is to start with batteries
all at the same state of charge.
Many
of the batteries are at different state of charge. A Cyclon
battery should read 2.14 volts when fully charged. The voltage
method of checking will give the state of charge (SOC) within 20
% if the battery has been resting for 24 hours before testing, or
within 5% if the batteries have been resting over 5 days. Some of
the batteries are reading less than one volt.
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