Posted: Sun Nov 13, 2005 7:08 pmAssuming an 100% efficient blower (impossible) the horsepower required to compress air thermodynamically. Temperature and barometric pressure will affect this, but for simplicity let's assume standard air conditions.
Hp = CFM x inches of water / 6339
By dividing that figure by blower efficiency you get the required total shaft drive power of the blower rotor(s). If the actual blower efficiency is not known, assume 40% as that is a fairly typical conservative figure for most vacuum motors and superchargers. You may actually do a little better than that, but don't count on it at the design stage.
Motor output horsepower can then be converted to watts by multiplying by 745.7
Motor input power = Motor output watts / motor efficiency
If the motor efficiency is not known, assume 85%. A more accurate figure can be worked out from the motor rating plate, if it has one.
Total Amps = Motor input watts / mains supply voltage
Here is a worked through example:
Hp = 500 CFM x 45 inches of water / 6339
Hp = 3.549
Shaft power = 3.549 / blower efficiency
Shaft power = 3.549 / 0.4
Shaft power = 8.8725 Hp
8.8728 Hp x 745.7 = 6,616 watts
Motor input power = 6,616 watts / motor efficiency
Motor input power = 6,616 watts / .85
Motor input power = 7,783 watts
Total Amps = Motor input watts / mains voltage
Total Amps = 7,783 / 240v
Total Amps = 32.43 A
So you can see a decent sized flow bench can be very power hungry !
Hp = CFM x inches of water / 6339
By dividing that figure by blower efficiency you get the required total shaft drive power of the blower rotor(s). If the actual blower efficiency is not known, assume 40% as that is a fairly typical conservative figure for most vacuum motors and superchargers. You may actually do a little better than that, but don't count on it at the design stage.
Motor output horsepower can then be converted to watts by multiplying by 745.7
Motor input power = Motor output watts / motor efficiency
If the motor efficiency is not known, assume 85%. A more accurate figure can be worked out from the motor rating plate, if it has one.
Total Amps = Motor input watts / mains supply voltage
Here is a worked through example:
Hp = 500 CFM x 45 inches of water / 6339
Hp = 3.549
Shaft power = 3.549 / blower efficiency
Shaft power = 3.549 / 0.4
Shaft power = 8.8725 Hp
8.8728 Hp x 745.7 = 6,616 watts
Motor input power = 6,616 watts / motor efficiency
Motor input power = 6,616 watts / .85
Motor input power = 7,783 watts
Total Amps = Motor input watts / mains voltage
Total Amps = 7,783 / 240v
Total Amps = 32.43 A
So you can see a decent sized flow bench can be very power hungry !