This is a page that describes how to configure a typical electrolyzer. Perhaps it will give you a starting point. We will limit the comments to Dry Cell configurations. These types of electrolyzers are currently the most efficient designs.
Plate Gap Voltage (PGV)
Voltage / # Electrodes} = PGV
or
Voltage / PGV = # Electrodes
or
# Electrodes * PGV = Voltage
In most cases, you should try to maintain between 2 - 2.4 volts per plate gap. All cells vary due to the following variables: voltage, amperage, electrolyte, plate material and temperature. So, your Plate Gap Voltage could vary somewhat.