I am using a Manual Schumacher, with a wider range of amp selections, so that when I run it at 20 amps, I am in the lower range of the settings that the charger was designed to handle.
I also use a lye bath, to reduce the run time in my Electro, and it also makes cleaning and maintenance of the electro easier.
I have not had any success with running a charger at 6V... the only switchable chargers I have, are Automatic chargers and they do not work well with electrolysis units.
When the concentration of Washing Soda is too high, it will cause my clamps to get VERY hot. I use less Washing Soda in Hot Weather, and more in Cold Weather.
My troubleshooting order, when charger clamps get too hot......
#1 - Check ALL connectors to the CI AND to the anode, clean or replace the connection points and hardware if corrosion is present
#2 - reduce to one piece in the electro (which is the normal for me)
#3 - reduce concentration of Washing soda
#4 - then I worry about the Battery Charger....