Reply by djg

Running 4.5” duct will really choke your air flow down to about 400 cfm regardless of the impeller size. At the static pressures for dust collection there is virtually no compression of the air so the air volume is limited by the smallest diameter pipe. For good dust collection you need to move twice that amount of air at the tool ports. 6” would be required for that. A 17” impeller is large for that motor. Your no load amps shouldn’t be much more than 6.3 amps. There are motor losses. If you block of the inlet, measure the current, you should get something in that range. Without the nameplate amps it is difficult to say how much current you will draw while processing air. Put a 6’ length of duct on the inlet of the collector and measure the current. If it doubles compared to no load, you may risk burning out the motor. Otherwise use 6” for everything. Your 6” duct system has to have more static pressure loss than a 6’ duct which means the system will draw even less current again meaning less heat generated by the motor doing work on that volume of air.

-- DJG