I recently set up a small backup power system with a Blue Smart IP22 charger (120V input, 12V 30A single output version) and 2 x 100AH LiFePo4 batteries. Works fine for charging the batteries, however once charge is done and it goes into float mode, there's some odd behavior. Specifically:
1) The voltage the charger reports (via Victron Connect bluetooth app) appears to vary up and down almost randomly by several hundred mv. It never exceeds the actual battery voltage as measured by an external meter, but drops down below it a lot.
2) The voltage as measured on the output terminals of the charger, and at the battery, is quite steady, but much higher than the configured float voltage (13.7v measured by several different meters, where the configured value is 13.4). When the charger is actually charging, its reported voltage matches exactly with external meter readings.
3) Brief pulses of current from the charger when its reported voltage is below 13.4v, which stop almost instantly when the reported voltage instantly goes up to match the actual battery voltage (13.7v).
What it kind of looks like to me is something like a diode in series with the output of the charger, so when it's not outputting any current, some internal capacitor discharges and it sees a lower voltage than the actual terminal/battery voltage. This causes it to start charging, which brings that capacitor back up to the actual battery voltage and charging ceases again. These brief pulses of current are enough to keep the battery voltage above the configured float value, since the charger does not "see" the actual battery voltage when it's not outputting any current.
Does that sound about right, and if so, is this normal/expected behavior for this charger when maintaining lithium batteries under zero load?
