I choose to upgrade to the WF-9855 convertor because I wanted 3 stage charging. Instructions for the replacement are not available from in the instruction manual but Randy at Best Converters is very knowledge and helpful.
The following is from the 9800 Series manual:
Microcontroller Function.
Our output voltage controlled microprocessor has been designed into
the converter PC board to avoid the need for additional equipment
when power is initially applied to the power converter, the microcontroller cycles though its mode to determine which mode it
needs. After the test cycle the power switches to Absorption mode(13.6VDC) when power is on.
When the output of the power converter is connected to a battery and
the load is applied (anything in the RV) the microcontroller checks to
see which mode it need to be in.
If the output voltage drops to 13.2VDC, the converter automatically
changes to Buck mode 14.4VDC. Normally when the output voltage
drops to 13.2VDC it means that the battery energy is less than 50%.
Under Buck mode when the power converter senses that out put
voltage is at 14.4VDC. It will change back to absorption mode. This is important to battery durability and battery life.
After a period of sensing no load the microprocessor automatically
places the converter in Float mode 13.2VDC. The design of out microcontroller is to senses the battery volt age then make a decision to select the proper mode automatically.
There must be a misprint because the output voltage drop is 12.2 volts (not 13.2 v) before the bulk mode starts
