Increasing output of the Dual Alternator Generator

By changing the arrangement of this device to belt drive and installing a new rotor in the PMA I am using 12 volts to make upwards of 108 VDC. However when I try to use it in a battery array it bogs down to 21 to 24 vdc and puts a strain on the drive alternator. I am testing large can capacitors to see if I can increase the amount of power the batteries get without a strain on the BLDC motor. Is there a way to take 108 Vdc and convert it to 120 Vac? Or 48 Vdc?