Hi I am building a high current PWM for H2=O generation. I'm using a linier power supply that I built from rewiring a microwave transformer, a bridge rectifier and a couple of caps. I've got 17 volts at 30+amps. I'm not at all good at design yet. I found a nice schematic for HHO generation but have a couple of questions bugging me. Down stream of the load he is using bank of Mos-Fets for the modulation. I've built a pretty good driver using a 555 that I'm able to vary both the duty cycle and on off time. I intend marry this in to the Mos-Fets he uses to actually pulse the load. He advises the use of Schotty diodes in parallel to the Mos-Fets. My question is why are they there and how do I calculate the size of them? My text books tell me what they are but not how to apply this knowledge.