Dale,Originally Posted by Dale Thompson
You and Terry are both right, but you are thinking about ducting resistance being the major load the motor must overcome instead of how much air is being pushed. For instance, in testing a friend's system with a 14" Jet impeller on my cyclone design it pulls 10.19 amps through his full ducting system with filters while moving a real 1200 CFM across a 3-car garage sized shop. Disconnecting the cyclone from the ducting and running it with just a short large diameter test pipe bumped the amps to 18.7 and the airflow to just under 1600 CFM. With the duct sealed so no air can move the motor fell to drawing only 8.78 amps. Both the ducting overhead and the amount of airflow are important.
bill