Will post a further update once the controller is done and tested.
If i was to break the bed up into 3 sections of 20 hexagonal cells each section would have a effective resistance of 1/( (1/22) * 20) = 1.1 ohms
Each section of bed would draw @12volts 12/1.1= 10.1 amps of current at 100% duty cycle
but this could be cut back to 2.5 amps once running @25% duty cycle, this could be done with a capacitor charge pump circuit of some sort or i could break each section down further into two this would give me a sectional current draw of 5.05amps @ 100% duty cycle and 1.25amps @25% duty cycle.
if was to run the coils at 24volts (like the good test showed is required) the sectional current draw would be doubled. with 3 sections each drawing 20amps @24volts ( and each sub section drawing 10amps) if i was to turn them all on at once i would need 60Amps of current at 24volts, this is unreasonable. but if i stagger fire each subsection @100% Duty cycle then cut back to 25% duty cycle i would need 10amps then 2.5amps per sub section.
the current profile would look like this
@ 10% Duty Cycle
@ 25% Duty Cycle
at 25% duty cycle the overlap turns out to be quite high.. i would need a PSU that spits out 25Amps @24 volts.. this is closer to reality but still a bit too far off i think.. i guess i will have to see what ebay has to say about the price of fish.. if i can find a 24V psu that is cheaper than further complicating the controller i wil do that other wise i will have to break down the coils into even smaller groups..
actually i have made an error.. the curve will look like this
worst case is that i end up with a nice 20Amp PSU for my printer. I was running the steppers off 24volts but got to tidying things up and switched back to 12volts..