In the simplest terms using 6"x6" plates and one cell stack like this -NNNNNN+ you can only apply 11.25 amps before you waste power and run into over heating problems.
If you want more gas you have to add more plates or another cell stack next to the first one like this -NNNNNN+NNNNNN- Now you can run up to 22.5amps with out over heating.
Hope this helps. "D"