Several years ago I choose to upgrade to the WF-9855 convertor because I wanted 3 stage charging for the Casita. I bought the WFCO 9800 Series from Best Converters. The converter worked fine for 4 years before it died. I contacted Best Converters and they told me the unit I had purchased was only lasting 3 or 4 years. I purchased IOTA-DLS 55 and I have been very pleased. The main reasion for the upgrade was to be able to leave the camper plug into AC power without worries of overcharging the battery.
The following information is from the orginal conversion but installing both units was identical.
Microcontroller Function copied for WFCO WF-9855 9800 Series Manual
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.