For the above example, the 12 V batteries may be selected as follows:
- Use 6 Group 27/31, 12 V, 105 AH batteries in parallel to make up 630 AH,
or
- Use 3 Group 8D, 12 V, 225 AH batteries in parallel to make up 675 AH
Charging Batteries
The batteries can be charged by using good quality AC powered battery charger or from
alternative energy sources like solar panels, wind or hydro systems. Make sure an
appropriate battery charge controller is used. It is recommended that the batteries may be
charged at 10% to 13 % of the Ampere Hour capacity (20 hour discharge rate). Also, for
complete charging (return of 100 % capacity ), it is recommended that a 3 stage charger
may be used (Constant current bulk charging followed by constant voltage boost /
absorption charging followed by constant voltage float charging )
Batteries, alternators and isolators on vehicles / RVs
It is recommended that for powering the inverter, one or more auxiliary deep cycle
batteries should be used that are separate from the SLI batteries. The inverter should be
powered from the deep cycle batteries. For charging the SLI and the auxiliary deep cycle
batteries, the output from the alternator should be fed to these two sets of batteries
through a battery isolator of appropriate capacity. The battery isolator is a solid state
electronic circuit that will allow the alternator to charge the two sets of batteries when the
engine is running. The isolator will allow the inverter to be operated from the auxiliary
batteries and also prevent the SLI batteries from charging the auxiliary deep cycle
batteries when the engine is not running. Battery isolators are available from auto / RV /
marine parts suppliers
A majority of smaller vehicles have 40 to 105 Ampere alternator and RVs have 100 to
130 Ampere alternator. When in use, the alternators heat up and their output current
capacity can drop by up to 25%. When heated up, their charging voltage may also not
reach the desired absorption voltage and will result in return of only about 80% of the
battery capacity. In case the current output of the standard alternator is not adequate to
charge the two sets of batteries rapidly and fully to 100% of their capacity, use heavy duty
alternator that can produce higher current and voltage required to charge multiple battery
systems. These alternators are available with auto / RV parts suppliers.
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