Battery Distribution Systems

All battery storage systems should be set up and used safely. All connections should be via fuses or circuit breakers and all cabling rated for it's purpose and fuse rating. Good quality battery isolation switches are recommended and suitable voltage and current meters (ammeters) should be installed.

In Figure 1, the various charging sources are fed via ammeters to show charging current and suitable fuses to the battery charging regulator (marked 'voltage regulator'). The output of this is fed via switches (or diodes) to the battery banks.

Figure 1. A typical small/medium size installation for cottage/boat/truck/caravan etc.

The output is fed via switching (and preferably overload cut-outs, not shown) to the various outputs. Battery outputs must always be fed through low voltage cut-outs where appropriate (most modern inverters incorporate this function internally), and via appropriately rated fuses or circuit breakers.

It is also recommend that each battery has it's own high current breaker or fuse mounted close to its terminals.

High current switches for two battery banks can be obtained from boat chandlers, as can many other useful items.

These outputs may be sent via different ammeters (small and large), or even from separate battery banks, with low power 'everyday' equipment on one battery and large inverters and power circuits on another for example.

Along with the ammeters there is also shown, a switchable voltmeter to check the state of the batteries.

Note that it is better to have two or more smaller banks of batteries that one large one. Batteries like to be discharged and charged, so one can be drained down toward its safe end point and then swapped for the other charged battery. The charging source is then applied to that battery until it is charged.

A back-up battery is also shown and this could be one that is designed specifically for standby use and will generally be smaller than the main batteries.

It is worth noting that if you intend to run mains voltage equipment via an inverter then it must be double insulated (i.e. the mains lead does not contain an earth), if the equipment requires an earth then this should be provided, if necessary using an earth spike. This is a copper covered steel pole specially designed for the job and is available from all electrical wholesalers. (They do last a long time even when banged into the average field etc., and removed umpteen times!).

If used within a metal bodied vehicle, then the bodywork can be used, (the neutral and earth of an inverter are usually bonded together and are often bonded as well to the battery negative, check yours with a multimeter). NOTE: This is only safe whilst used within the confines of the vehicle, if the equipment, any part of, or anything connected that may possibly be conductive, is accessable from outside the vehicle, it must be earthed properly

12V lead acid batteries - Voltage references:

Lead Acid (liquid electrolyte): Charge/discharge voltages:

SOC= State Of Charge

11.7V - Prewarning: SOC<40%
11.1V - Disconnection: SOC<30%
12.4V - Reconnection: SOC>50%

11.7V - Commence Equalisation charge (14.7V) (this means that if the battery has reached this level of discharge or beyond, it should ideally receive a charge at 14.7V)

12.6V - SOC<70% Cycle charge (14.4V) (this means that if the battery has been discharged beyond this point, it should ideally receive a charge at 14.4V, the standard charge voltage like that on a car alternator).

13.7V - Final charge voltage
Temperature compensation: -4mV/K/Cell (ideally, but not often used!)