05-14-2015, 09:58 AM
Yep - centrifugal machines all have the same characteristic; less resistance to flow = more power requirement.
Shopvac blowers are a multi-stage centrifugal blower, so minimum motor amps is at no flow. That is why a Shopvac increases in pitch when you block the flow. Works the same with liquid centrifugal pumps.
Induction motors run at a speed slightly less than their "synchronous" speed. In North America we have 60 Hz power, so the synchronous speeds are:
2 pole: 3600 rpm and operate around 3450 rpm
4 pole: 1800 rpm and operate around 1750 rpm
6 pole: 1200 rpm and operate around 1150 rpm
Induction motors run at their highest speed (close to synchronous) with no load.
As load increases, the "slip rate" increases to generate the needed power and the motor slows down.
The motor nameplate rpm will be at the nameplate rated horsepower.
For a motor - blower combination, the blower and motor balance at a speed where blower hp = motor hp.
At this speed, the running amps need to be less (or equal to) the nameplate amps or the motor will overheat.
Terry S.
Shopvac blowers are a multi-stage centrifugal blower, so minimum motor amps is at no flow. That is why a Shopvac increases in pitch when you block the flow. Works the same with liquid centrifugal pumps.
Induction motors run at a speed slightly less than their "synchronous" speed. In North America we have 60 Hz power, so the synchronous speeds are:
2 pole: 3600 rpm and operate around 3450 rpm
4 pole: 1800 rpm and operate around 1750 rpm
6 pole: 1200 rpm and operate around 1150 rpm
Induction motors run at their highest speed (close to synchronous) with no load.
As load increases, the "slip rate" increases to generate the needed power and the motor slows down.
The motor nameplate rpm will be at the nameplate rated horsepower.
For a motor - blower combination, the blower and motor balance at a speed where blower hp = motor hp.
At this speed, the running amps need to be less (or equal to) the nameplate amps or the motor will overheat.
Terry S.