Blower impellor size

I needed to ensure that the motor will not be over stressed by having too much load on it. This is done by choosing the correct impellor size. The jig in the photo shows the motor with a wooden batten attached which quite closely simulates the load of an impellor of the same diameter. Using a Watt meter, and adjusting the length of the arms ensures that the motor spins up to speed and draws the correct power.