Owner`s manual

VANNER Incorporated Theory of Operation

70-Series Power Management System OWNER’S MANUAL

Theory of Operation

In many 24 volt electrical systems it is desirable to tap into the battery system to obtain power for 12 volt

loads. This method, while seemingly simple, causes a charge imbalance resulting in Battery B (see

diagram) being overcharged, and possibly boiling, while Battery A discharges.

To solve this application problem the Vanner VANN-Guard is connected to the battery system at the +24

volt, +12 volt, and ground points. The VANN-Guard makes the batteries look like they are in series and in

parallel at the same time. The VANN-Guard maintains the voltage balance and therefore the charge

acceptance rate of each battery. The VANN-Guard hold Battery A and B voltages to within 0.05 volts

under light loads and to within 0.1 volts at full rated load.

When the voltage of Battery A is higher than or equal to Battery B the VANN-Guard is in the standby

mode, i.e., it is not transferring power from its 24 volt input to its 12 volt output. When a 12 volt load is

present, and Battery A's voltage decreases to just below the voltage of Battery B, the VANN-Guard

activates and transfers sufficient current from Battery B to Battery A to satisfy the load and maintain an

equal voltage and charge in both batteries.

A key advantage of a system containing a Vanner VANN-Guard, compared to a DC to DC converter, is

that if the 12 volt load requires a momentary surge current which exceeds the rated capacity of the

VANN-Guard, Battery A will supply the extra current to the load. The VANN-Guard will then replenish the

energy to Battery A after the surge has passed.

The following scenarios describe the VANN-Guard Power Management System operation.

Scenario #1 - 24 volt load present, no 12 volt load present. The system operates as a system would

without the VANN-Guard whether the alternator is ON or OFF. The VANN-Guard is in the standby mode

except for making small adjustments to keep the batteries in balance.

Scenario #2 - Both 24 volt and 12 volt loads present, alternator is OFF. The VANN-Guard will insure

that both batteries will discharge at the same rate even if different loads are present.

Scenario # 3 - Both 24 volt and 12 volt loads present, alternator is ON. The alternator provides 24

volt power to the battery system and to the 24 volt loads. The VANN-Guard transfers power from the 24

volt source to the 12 volt load by converting 24 volt power to 12 volts. It will supply sufficient 12 volt

power to satisfy the 12 volt load and to maintain battery voltage balance.

12 V

Battery A

+12 Volt

Loads

+24 Volt

Loads

12 V

Battery B

24V

Alt

VANN-Guard

+24V

GND

+12V

+24V