Calling It Like It Is

HORSEPOWER

CALLING IT LIKE IT IS

There seems to be some confusion around machinery showrooms as to what constitutes the right horsepower rating for a given motor. Some machinery resellers, aware that Aussie woodworkers are a power hungry lot,
s-t-r-e-t-c-h the reality a bit by quoting the horsepower of the motors on their brand of machinery in terms of Peak Horsepower and therein lies the problem for a buyer comparing one machine against another very similar unit. Unfortunately they forget to include the words “Peak Horsepower” in their description.

An electric motor is destined to generate a certain horsepower by virtue of its physical size, gauge of wiring, and volume of wire. The construction of the rotor in an induction motor also influences the out put of the motor. A motor, once designed and built, will only deliver the power limited by the above factors.

However…as with all things, there is a grey area, and in an electric motor, the grey area is the ability of a motor when stressed, to deliver a fraction of power above its design output. That ability is defined as Peak Horsepower. What it means is that the motor will, for a short time, increase its draw on the power supply, and pump out a little extra grunt.

It is this ability which enables you to cut through a section of timber which is denser and harder than the machine was really designed to deal with.

But, there is a penalty. The penalty in this instance is heat. Significant additional heat load is generated during this demand time, and the heat can cause damage to the insulation on the wiring of the fields and leads, and can cause damage to the epoxy binders in the windings of the motor. Sustained heat will of course lead to breaching of the insulation between the wires in the motor, a short circuit is created, or more regularly, the heat causes the wires to melt and, now wait for it, this is important, the smoke, installed at time of manufacture by every motor manufacturer will escape*. This becomes evident by a tell tale wisp of smoke curling out of the motor housing, and often accompanied by an odour easily detected by a machine operator. Once the smoke escapes, that’s it! You can’t get it back into the motor. The motor is now dead. Rewind, replace whatever, but it won’t go.

Many motors are protected by an overload cut-out which is designed to protect the motor against drawing above its design capacity. But not all.

So, for a few seconds, a 3/4HP motor can be a 1HP motor. True. It is a fact. But not for long, and it seems a bit deceptive to claim a machine is equipped with a 1HP motor when other resellers have the same or very similar machines on sale with an advertised 3/4HP motor.

So, buyer be informed….a motor of one horsepower can be a motor of a greater horsepower…….but not for long.

1 Horsepower = 750watts.

* Yes, this part is tongue-in-cheek.