Both models, the IPA04-HC and IPA15-HC require a minimum regen resistor (braking resistor) value of 22 Ohm.
How to calculate regen requirements is available here: Regen Calculations
IPA04-HC (400W) bus capacitance is about 1680 uF
IPA15-HC (1500W) bus capacitance is about 2800 uF
glh Nov 2020