Here is the formula of Charging Time of a Lead acid battery.
Charging Time of battery = Battery Ah / Charging Current T = Ah / A
Example, Suppose for 120 Ah battery, First of all, we will
calculate charging current for 120 Ah battery. As we know that
charging current should be 10% of the Ah rating of battery. so
charging current for120Ah Battery = 120 x (10/100) = 12 Amperes.
but due to losses, we can take 12-14Amperes for charging purpose.
suppose we took 13 Amp for charging purpose, then charging time for
120Ah battery = 120 / 13 = 9.23 Hrs. but this was an ideal case...
practically, this is noted that 40% of losses ( in case of battery
charging) then 120 x (40 / 100) = 48 .....(120Ah x 40% of losses)
therefore, 120 + 48 = 168 Ah ( 120 Ah + Losses) Now Charging Time
of battery = Ah/Charging Current 168 / 13 = 12.92 or 13 Hrs ( in
real case) Therefore, an 120Ah battery would take 13 Hrs for
completely charging ( with 13 A charging current). Most battery
manufacturers recommend sizing the charger at about 25% of the batt
ery capacity (ah = amp hour capacity). Thus, a 100 ah battery would
take about a 25 amp charger (or less). Larger chargers may be used
to decrease charge time, but may decrease battery life. Smaller
chargers are fine for long term floating, e.g. a 1 or 2 amp "smart
charger" can be used for battery maintenance between h igher amp
cycle use. Some batteries specify 10% of capacity (.1 X C) as the
char ge rate, and while this doesn't hurt anything, a good
microprocessor charger of the appropriate charge profile should be
fine up to the 25% rate. You talk to di fferent engineers, even at
the same company, you get different answers. For example, if your
portable guitar amplifier is drawing a steady 20 amps and y ou want
it to last 1 hour you would start out with Step 1: C=20 amps * 1
hour = 20 AH Then proceed to Step 2 C = 20 AH / 0.8 = 25 AH
Then take the high rate into account C =25 /.5 = 50 AH Thus you
would need a 50 amp hour sealed lead acid battery to run the
amplifier for 1 hour at 20 amps average draw. -------------400AH
battery drawing load of 45A Discharge Time: 400/45*0.5*0.8= 3.5 Hrs
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