Split Charging.

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Most marine craft have split-charging facilities for two or more battery banks. This is less common with road vehicles, but useful with eg. ambulances and mobile libraries etc.

ADVERC Battery Management can be safely used with all types of split-charging systems, the commonest of which are listed below:

The Battery Selector Switch:

A well tried method featuring the 1, 2, or BOTH principle. ADVERC is perfectly at home with this equipment, the single ADVERC battery sensor (red) being connected to the common pole on the switch.

This method puts the onus on the individual to select a particular battery bank for charging. Automatic switching to the 'BOTH' position is not always preferable.

In this position, the alternator would have to charge the full complement of batteries. Moreover, different states of charge between battery banks could also be present, allowing the higher bank to drain into the lower in order to reach voltage equilibrium i.e. the benefit of an already highly charged battery bank would be lost.

Judicious use concerning battery selection enables rapid charging to be achieved, especially when using an ADVERC DCM (Digital Circuit Monitor).

The Blocking-diode:

Blocking-diodes are loved and hated. Whilst battery charging is automatic, with provision for battery dedication eg. for engine starting, instruments, refrigerator, anchor-winch etc., there can be up to 1v drop across the diode. This is a disaster for battery charging employing conventional voltage regulators and machine-sensed alternators. Blocking-diodes should never be used with standard alternator regulation.

ADVERC Battery Management compensates for this voltage drop, however, so the benefits of automatic charging are retained, without the shortcomings.

Note 1: Ideally, the blocking-diode rating should be 20 amps greater than the maximum alternator output rating.

Note 2: It is rare, but possible, with extended engine use e.g. 24hrs and a large domestic battery capacity, to slightly overcharge the engine-start battery when using a blocking-diode. If this is likely to be a regular occurence, the following is recommended: Use a manual or remote electrically operated isolator switch to isolate the engine-start battery (see Ideal Boat Electrics).

The engine electrics will continue to function and it is impossible to forget that the battery is isolated - the engine will not start!

The Relay Method:

As the cheapest approach to split-charging, the relay is more common with road-vehicles than boats.

The engine battery is left in circuit during ignition 'off'. The auxiliary battery is 'paralleled' when the engine is fired-up i.e. both battery banks are charged simultaneously.

This method is reasonably effective where the engine is running for long periods though there is a disadvantage in that a heavily discharged auxiliary battery can drag down the engine battery voltage, due to imbalance. Heavy loads have been known to melt the relay!

As a safety precaution against relay failure, connect the ADVERC battery sense lead (red) to the engine start battery, which is permanently connected to the alternator supply.

Blocking-diode & Battery Selector Switch Combination:

Though not common, our opinion is that this is the most effective method of split-charging where the advantages of the Blocking-diode method are employed in charging the batteries and the Battery Selector Switch is used to distribute battery output combining automatic charging with flexibility in terms of battery selection (see Ideal Boat Electrics).

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