Re: [CAD_CAM_EDM_DRO] more horsepower (defs)

ballendo@... wrote:

> Doug H wrote:
> >One horsepower equals 746 watts in the same way one gallon equals
> >231 in**3 or one inch equals 25.4mm. One HP will always equal
> >746W or 550 ft.lb/s because it is a unit of measure.
>
> Doug,
>
> Yes, an arbitrarily decided unit of measure. The question HERE (in
> this thread) is whether it is a GOOD unit of measure compared to the
> mechanical definition. Is horsepower about power CONSUMED or power
> OUTPUT? Are the two REALLY equivalent?

Power is power. But, the rating on a motor is customarily defined as the
power it can output under the conditions specified, and for the duration of
the period in the rating. (Most AC induction motors carry continuous
ratings.) Some inductrial motors are actually rated ABOVE the nameplate
rating, ie. compressor duty motors with "service factors' of 1.15, would mean
that the motor has been tested to deliver 115% of the nameplate rating without
damage for an extended period.

> >Perhaps it is difficult to see how mechanical HP can be equivalent to
> >electrical power. If you took Watt's horse and hitched it to a
> >friction device, that device would produce heat equivalent to a
> >resistive element that consumes 746 watts.
>
> Doug,
>
> Thank you for the comparison. Is this the reason 746 Watts was
> chosen? Can you provide a link or reference? Seems like an awful lot
> of variables here...

746 watts can be converted to joules/sec, and the ft-Lb - seconds rating can
also be converted to Joules/sec, and the numbers will be the same.
These numbers are in every physics and electrical reference book.
I haven't taken the time and effort to build the equipment to check these
numbers, I trust that if the equivalence is shown exeactly the same in
literally hundreds of reference books, people must be pretty sure
of its accuracy. You will note that international motors are normally
rated in KW output, and have no HP rating.

Jon