A note about shop vacuums and horsepower…
For years I’ve scratched my head how manufactures advertise these massive horsepower ratings so I’ve done some digging and here’s what I’ve come up with.
I'm not an electrician bit common sense tells me when Craftsman and several other vacuum manufactures boast about Peak Horsepower I get this feeling that I should immediately sit done to protect myself...
The numbers
- 1 horsepower = 745 watts
- Watts Volts = Amp
Craftsman (6.5hp X 746) / 115 volts = 45.25 amps
RIGID (5hp X 746) / 115 volts = 32.5 amps
Shop-Vac (6.5hp X 746) / 115 volts = 45.25 amps
Regardless of manufacture, they all do it and in my opinion BS...
I guess I should be running my old Craftsman vacuum on a
#6 wire and a 50amp circuit breaker but I never have. It's always run fine on a standard 15amp circuit breaker...:dunno:
So, is this horsepower thing just a gimmick? Mostly.
The underlying truth of what the manufacturer is probably not telling you (or the salesperson simply doesn't know), is that a so-called "five horsepower" device really means that, under very particular conditions, it is capable of developing 5 HP of peak power -- for a very brief interval of time. This is not continuous, full-load power. Note that they might use the term "develops" or "peak" immediately preceding the horsepower figure in the rating claim. Often stated as "develops 5 HP."
The peak power of a motor in this situation is calculated by measuring its electrical power consumption at its stall torque, as simulated in a laboratory. A mechanical load such as a braking mechanism is applied to the running motor, which causes the shaft to stop turning. At that precise moment in time, the motor will draw its peak electrical power (kids, don't try this at home). At that point, the motor is suddenly drawing an abnormally high amount of current -- a phenomenon called "locked rotor current," which is similar to inrush current. You may witness this phenomenon when your circular saw momentarily binds up while cutting wet wood (notice how the lights dim when this happens!).
The whole concept of peak power is silly, because the motor is not intended to be operated in this condition for more than a brief interval. It is not a practical measurement of the motor's true capabilities.
A motor in a device such as a saw is better defined by the power delivered while continuously doing its intended job - cutting wood! Stalling an electric motor for more than a few seconds will cause it to heat up and possibly burn out, though your circuit breaker will (hopefully) trip first. The motor is, for a very brief moment, drawing much more current than normal.
The manufacturers cleverly use this abnormally high electrical current transient to
calculate its "peak" horsepower, using the same equation discussed above. This mathematical sleight-of-hand affords the manufacturer some distorted bragging rights as to power. Take a look at the amperage, the secret lies here...
In short, it's a way to deceive the customer into thinking horsepower is king..........It is but only on the racetrack...
rops:
