The primary function of an automatic charging relay (ACR) is to combine battery banks so that they can share the output of a single charger. In some charger installations, there may be problems associated with the charger "Float Mode" and ACR performance.
A Normal Charging Cycle is shown below left. Chargers also can advance through stages in other ways. Some multi-stage chargers advance through the various stages of charging to the low output Float Mode quite quickly. Or if a charger recognizes a fully charged battery bank, it may advance directly to the Float Mode. An example is shown below right. Float Mode voltage levels sometimes fall below the connect thresholds of most ACR's. Therefore, the battery banks may not be combined to share in charging.
Blue Sea Systems' 120 Amp SI ACR, part number 7610, overcomes this problem with its dual voltage threshold that turns ON and connects batteries if the charging voltage exceeds:
|•||13.5 Volts sustained for 30 seconds (as shown below left)|
|•||13.0 Volts sustained for 120 seconds (as shown below right)|
The ability of the 120 Amp SI ACR to connect batteries when the changer output is 13.0 Volts for 120 seconds allows the ACR to recognize Float Mode as a charging state. Furthermore, this feature reduces the potential for excessive rapid cycling by using a longer time delay when the voltage difference between the connect level and the isolation level is small.