"Christopher Tidy" wrote in message
...
Hi all,

This group often sees questions about ratings (can my 2 hp electric
motor develop 3 hp? can I draw 150 A from my 100 A supply? etc.) so
I'd
like to ask a rating question. I think this one might spark some
debate.
If you buy a good electric motor, the power rating is a continuous one
(or it says otherwise). Same with most pieces of industrial equipment.
But what about a car? Is the 130 hp or whatever maximum engine power
the
manufacturer quotes a continuous or an intermittent rating? I was
always
under the impression that it was an intermittent rating, though quite
where I got that idea I can't remember. I'm not asking if the engine
will wear out quickly developing its maximum power rating
continuously -
I'm sure it will - I'm just wondering if it will overheat?

Any thoughts? Just a matter of curiousity...

Best wishes,

Chris


HP is not directly measured in either case. It is based on an equation
using the torque and RPM. In a normal auto engine the torque and HP both
have a peak number. That is the number most often quoted. If the cooling
system is properly designed for the engine it will not overheat BUT it
will run warmer than it normally would. However most AUTO engines built
cannot handle running at the max numbers for long because they are made
so light to save fuel.



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In article ,
"Steve W." wrote:



HP is not directly measured in either case. It is based on an equation
using the torque and RPM. In a normal auto engine the torque and HP both
have a peak number. That is the number most often quoted. If the cooling
system is properly designed for the engine it will not overheat BUT it
will run warmer than it normally would. However most AUTO engines built
cannot handle running at the max numbers for long because they are made
so light to save fuel.


The rule of thumb we used for sizing brakes for overhead crane motors
was:

5250 X RPM / HP = torque

Should be able to get the HP as the unknown with a little algebra.






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"John Husvar" wrote in message
...
In article ,
"Steve W." wrote:



HP is not directly measured in either case. It is based on an equation
using the torque and RPM. In a normal auto engine the torque and HP both
have a peak number. That is the number most often quoted. If the cooling
system is properly designed for the engine it will not overheat BUT it
will run warmer than it normally would. However most AUTO engines built
cannot handle running at the max numbers for long because they are made
so light to save fuel.


The rule of thumb we used for sizing brakes for overhead crane motors
was:

5250 X RPM / HP = torque

Should be able to get the HP as the unknown with a little algebra.



Hi John

The equation in your post has been published with a significant error. I
am sure it is a "typo". HP equals Torque times RPM.
Yeah, the automotive design guys *do* measure the HP of the engines they
develop.

It is kinda interesting that at about 5,250 RPM the Torque *and* the HP
are the same number when measured with the commonly used USA dimensions.
So, an engine producing 200 HP at 5,250 RPM will be producing 200 ft lbs
of Torque.

Jerry

"Jerry Martes" wrote in message
news:GffSf.12418$%e1.4667@trnddc05...

"John Husvar" wrote in message
...
In article ,
"Steve W." wrote:



HP is not directly measured in either case. It is based on an
equation
using the torque and RPM. In a normal auto engine the torque and HP
both
have a peak number. That is the number most often quoted. If the
cooling
system is properly designed for the engine it will not overheat BUT
it
will run warmer than it normally would. However most AUTO engines
built
cannot handle running at the max numbers for long because they are
made
so light to save fuel.


The rule of thumb we used for sizing brakes for overhead crane
motors
was:

5250 X RPM / HP = torque

Should be able to get the HP as the unknown with a little algebra.



Hi John

The equation in your post has been published with a significant
error. I
am sure it is a "typo". HP equals Torque times RPM.
Yeah, the automotive design guys *do* measure the HP of the engines
they
develop.

It is kinda interesting that at about 5,250 RPM the Torque *and* the
HP
are the same number when measured with the commonly used USA
dimensions.
So, an engine producing 200 HP at 5,250 RPM will be producing 200 ft
lbs
of Torque.

Jerry


HP = Torque (lbft) X RPM / 5252



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The fundamental formula for horsepower sez:

HP = [ (WRN x 2 pi) / 33000 ] Visualize a rope on a windlass arrangement
wound around a shaft of radius "R"; the rope is supporting a load of "W",
and the shaft is turned at a number of revolutions, "RPM"

Whe R = Radius or length of a lever arm about the center of a shaft, in
feet
W = force, weight, in pounds
N = Number of revolutions, RPM

Supposedly, this is the original formula, traceable to James Watt.
Simplifying the formula by dividing out the 2 pi term yields: HP = [ WRN /
5252 ] WR is torque, thus the familiar form becomes: HP = [ (Torque x RPM)
/ 5252 ] or Torque = [ (HP x 5252) / RPM ]

Bob Swinney