Battery Relay? Battery Diode? Battery Combiner?
Split Charger? Split Charging?

Many commercial vehicles are fitted with multiple battery banks. Each must be able to be discharged fully without pulling power from other battery banks while all need to be charged from the same charge source(s).

While this may sound simple, it is commonly misunderstood and many legacy devices are fitted that introduce more problems than they solve: Battery Isolators/Blocking Diodes: A diode allows power to flow only in a single direction.

When two (or more) are linked between an alternator (or other charge source) and say, two batteries, they allow both to charge without allowing them to cross flow during discharge. Diodes naturally introduce voltage drop. This means that the battery does not see the correct charge voltage and never reaches 100%. What’s more, diodes act like a non-return valve and cause overcharge where small and large batteries are mixed in the same system. FET/Electronic isolators and Smart alternator controllers promise to solve the voltage drop issue (which they do) but actually increase battery overcharge damage.

Split Charge Relays: Split Charge Relays are linked between the engine and auxiliary battery bank. When the ignition is switched on, they energise and parallel the batteries for charging. Charging both batteries in parallel is the best method pos-sible (no voltage drop or force feeding). However, if the auxiliary batteries are very low and the engine is started; any high load on the auxiliary battery bank will result in large currents being drawn across the split charge relay. This results in melt-down of the relay and sometimes causes fire.

Modern split charging systems combine (parallel) batteries for split charging. No voltage drop or over-charge occurs. Built in smart control and monitoring systems prevent relay overload and in some cases are adjustable to achieve exact power balance across the electrical system.

Voltage Sensitive Relays (VSRs)/Automatic Charge Relays (ACRs): VSR’s have a built in voltage monitoring circuit. When voltage is above the Connect Voltage, they parallel the batteries. When it falls below the Dis-connect Voltage, they disconnect. Merlin VSRs are Bi-Directional. This means that they monitor both batteries and handle all charge sources on board. Perfect for smaller electrical systems but should be used with care on large systems and where charge sources are under-sized (due to rapid cycling of the relay).

Battery Combiners/SmartBanks: Combiners work in the same way as a VSR. However, Connect Voltage and Disconnect Voltage are configura-ble. This allows you to ensure that engine batteries are charged properly before connecting auxiliaries. A Timed Hold delay feature prevents rapid cycling of the Split Charge Contactor on systems where very large battery banks are fitted, large loads are present or where charge sources are undersized. Some Combiners feature an Emergency Parallel switch. When activated, this allows ‘Jump Start’ of the engine if the engine battery fails; Or, to allow auxiliary loads (eg VHF radio & nav equipment) to be run from the engine battery for a limited peri-od of time.

Emergency Parallel saves expensive call outs on the road and potentially dangerous situations at sea. In Emergency Service Vehicles, adjustable split charging is crucial to vehicle reliability. Due to short journey times, quick connection of split charging is necessary (without compromising chassis electrics) otherwise no power reaches the Auxiliary batteries. Non-adjustable split chargers do not allow this. SmartBank is a perfect solution to the problem. Battery Combiners are ideal for all applications. Multiple combiners and different combinations of Split Charge Contactors can be used to achieve complex and advanced systems. Careful placement of contactors can also determine the order in which batteries charge/discharge and prioritize them accordingly.

More Battery Run-Time Without Adding Batteries!