In a boat with two battery banks, it is useful to be able to charge both banks while underway. Charge management devices connect two battery banks when charging, and isolate them from each other when not charging. If one battery becomes depleted, there will be a charged bank available for emergency starting.

There are two main types of charge management devices used on boats:

Automatic Charging Relays (or Voltage Sensitive Relays) use a relay combined with a circuit that senses when a charging source is being applied to either battery. When a charge is being applied, the ACR combines the batteries. When there is no charge present, the ACR isolates the batteries.

Battery Isolators are one-way electrical check valves that allow current to flow to, but not from, the battery. Their disadvantage is that the diodes used to achieve this cause a voltage drop that consumes charging energy, creates heat, and causes batteries to be undercharged. Although alternators with external voltage sensing can correct for undercharging, voltage drop and heat remain a problem.

When choosing an ACR:

Current Management. ACRs can potentially be exposed to very high currents if the engine is cranked while the ACR has combined the batteries. This can occur when a charge source other than the alternator, such as a solar charger, has caused the ACR to close. Blue Sea Systems uses two methods to overcome this. ML- Series ACRs have high amperage contacts rated for engine starting, and the SI- Series ACR momentarily opens the relay, isolating the two batteries during starting.

Remote Control. Blue Sea Systems ML- Series and SD-Series ACRs include a Remote Control Contura Switch so that ACR function can be controlled from a helm station or other convenient location.

Manual Override. In addition to the remote control switch, ML- Series ACRs are available with a local manual control knob to combine battery banks in an emergency.

Start Isolation. All Blue Sea Systems ACRs can be configured for Start Isolation, which provides temporary isolation of house loads from the engine circuit during engine cranking. This protects sensitive electronics from voltage sags and spikes in the starting circuit.