WFCO WF-8900MBA Series, Operator'S Manual

5

DC Fuse Board

OPERATIONAL FEATURES
Converter Operation Modes

Three-Stage Smart Charging

In order to maximize battery life, it is best to charge batteries slowly, keep them topped off 

with a trickle-charge when the RV is not being used. The 3-Stage “smart” charger 

continuously measures the battery voltage output and regulates the amount of charge using 

three modes of operation; Absorption, Bulk and Float modes. 

All WFCO power converters are automatic three-stage switching power supplies. The 

converter senses which mode it needs to be in by checking the RV system voltage.

The converter normally provides a constant target output voltage of 13.6 volts (nominal) to 

power all the branch circuits. However, it is current limited, and if the output (load) 

current reaches its maximum, the output voltage will drop as necessary to hold the 

converter’s maxi-mum output current level (the amperage rating) without exceeding it. 

If the output current reaches its maximum (normally caused by a discharged battery), this 

will cause the converter to go into Bulk Mode, which means the target output voltage will 

change to 14.4 volts and a timer will start. Although the converter is outputting 14.4 volts, 

you will not be able to read that on a voltmeter due to the voltage-current relationship.

From the paragraph above, as load current increases, output voltage decreases. The actual 

out-put voltage will not rise until the load current is reduced, which happens naturally as 

the battery charges or if 12-volt appliances are turned off. 

Bulk Mode will be maintained until the current draw drops to approximately five Amps, 

or until the timer reaches four hours (whichever happens first). Then the target output 

voltage is changed back to 13.6 volts for Absorption Mode. Lights that are powered from 

the output may change brightness slightly at that time.

Figure 1