it seems that rather than add on a bolt on electrical kludge, the straight forward solution would be to retro the newer models back to the way the older models (the ones with fewer problems) work.
Except the chain drive did create maintenance issues. Reliability also, if the chain was not maintained. The newer setup is simpler and less costly to manufacture, even with the mode switch added in. The early direct drive systems' grate speed was higher than optimum, and much higher than with the chain drive. Now the grate speed can be electronically controlled with great flexibility.
I've read over the last couple of pages describing the new mode switch option and understand it's great adjustment flexibility. What's missing is the desired grate speed, or range of speeds for optimum operation. So my question goes to AHS ... what is the speed, rate of grate travel (inches/per minute) for satisfactory operation? How did you determine the necessary speed range? Once we know the desired speed there are many possible implementations.
My AHS 130 uses the older percentage timer control and a fixed speed chain drive. This system is not a feedback control system, it's just open loop. Once the burning height is properly established, by stopping or forcing ashing, the percentage timer controls the boiler just fine. I haven' had a "puff back" in years.
I've been critical of the thermo-ash control feedback control system. It seems to me the "new" mode switch design is just a new implementation of the older percentage timer open loop control system. I fail to understand how making a temperature measurement, especially with a thermocouple, under the grate is sufficiently correlated to fire height in the antratube or combustion parameters that would cause a puff back. For any closed loop control system to work, the measured parameter, temperature in this case, has to be related to what you are trying to control. It's just not in this case. Wrong feedback sensor in the wrong position.