7.Charging Formula
( A ) . Charging Time
Formula
Example
Charging time will depend on the capacity of your battery and on how
deeply it is discharged. The following equation calculates an approximate
charging time.
Charging time =
where:
Charging Time: Battery recharge time in hours
CAP: Battery capacity in amp-hours
DOD: Battery depth of discharge in per cent. A fully
discharged battery has 100% DOD
CC: Charge current, the rated current output of the
charger in amperes
80%: Typical charging efficiency forlead-acid batteries
A Group size battery rated at 100 amp-hours is 40% discharged, that is,
it has a DOD = 40. Charging time with a C-15L-12 unit is
calculated as follows:
Charging time = = 3.3 hours
CC x 80%
15A x 80%
100Ah x 40%
CAP x DOD
( B ) . Discharging Time
To achieve 50% cycling you should calculate your Amp-hour consumption between
charging cycles and use a battery bank with twice that capacity. To calculate Amp hour
consumption, first look at the rating plate on your AC appliance or tools.
Each appliance or tool will be rated in either AC Amps or AC watts or AC VA(Volts-Amps)
apparent power.
Use one of the following to calculate the DC Amp-hour draw for a 12 Volt system:
(AC Amps x 10) x 1.1 x hours of operation = DC Amp-hours
(AC watts/12) x 1.1 x hours of operation = DC Amp-hours
(AC VA/12) x 1.1 x hours of operation = DC Amp-hours
In all formulas, 1.1 is the factor for inverter/charger efficiency.
Calculate the above for every AC appliance or tool you intend to use on your inverter.
This will give you the total number of Amp-hours used between recharges. Size your battery
bank using this number as a guideline. A good rule to follow is to size the battery bank about
2 times larger than your total Amp-hour load requirement. Plan on recharging when 50% discharged.
Many electric motors have momentary starting requirements well above their operational rating.
Start up watts are listed where appropriate. Individual styles and brands of appliances may vary.
NOTICE: Lead-acid battery is recommended for inverter/charger models, also the LiFePO4 battery.
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