RECHARGE
The normal method of solar charging is to charge at the current available from the
solar array up to a maximum of 30%C
100
Amps until the battery voltage reaches
2.40/2.45Vpc. This period is referred to as the
‘bulk charge’. The regulator then
controls the charge voltage at 2.40/2.45Vpc for a set period of 2 to 4 hours. This is
termed
‘absorption time’. The charge then reverts to the ‘float charge’ at 2.27Vpc.
During this charge, acid is released from the plates and because it is heavier than
the surrounding electrolyte it sinks to the bottom of the cell.
With the above charging regime the battery may receive sufficient charge on a good
irradiation day to fully convert the active materials but, because there is no vigorous
gassing of the electrolyte, the acid that has been released from the plates remains at
the bottom of the cell. This results in weak acid at the top of the cell and strong acid
at the bottom. This is called stratification and can cause deterioration of the plates.
To prevent stratification damage it is recommended that the battery be given an
equalisation charge every 20 days. This mixes the electrolyte and brings weaker
cells into line with those that are stronger.
Initially, top of charge specific gravities should be in the range 1.250 to 1.270 but
these may rise above 1.270 over the first few weeks of operation. This is normal and
is not detrimental to the performance of the battery. However if the specific gravities
rise above 1.300 they should be adjusted downward (see Adjustment of Electrolyte
Specific Gravity).
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N
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DEPTH OF DISCHARGE (AS % OF 100 HOUR CAPACITY)
EXPECTED CYCLE LIFE Vs DAILY DEPTH OF DISCHARGE
