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PS versus BHP
- Subject: PS versus BHP
- From: Jim Huber <jhuber@xxxxxxxxxxx>
- Date: Wed, 1 Mar 2000 11:37:40 -0800
from http://www.fwkc.com/encyclopedia/low/articles/h/h011001344f.html
HORSEPOWER, unit of power in the English system for measuring the rate at which
an engine or other prime mover
can perform mechanical work. It is usually abbreviated hp. Its electrical
equivalent is 746 W, and the heat equivalent is
2545 Btu. One horsepower was originally defined as the amount of power
required to lift 33,000 lb 1 ft in 1 min, or 550
ft-lb per sec.
The British engineer and inventor James Watt established this value for the
horsepower after determining in practical
tests that horses could haul coal at the average rate of 22,000 ft-lb per min.
He then arbitrarily raised this figure by a
factor of one-half to establish the current value. In the metric system, 1 hp
is sometimes called force de cheval or
cheval-vapeur and is defined as 4500 kg-m per min, which is equivalent to
32,549 ft-lb per min, or 0.986 of the
English horsepower unit.
<this probably explains the difference between PS and BHP> ... Jim
Three different horsepower values are used to quote the performance of an
engine: (1) Indicated horsepower is the
theoretical efficiency of a reciprocating engine, which is determined from the
pressure developed by the cylinders of
the engine; (2) brake or shaft horsepower is more commonly used to indicate
the practical ability of the engine, or the
maximum performance, which is the indicated horsepower minus the power lost
through heat, friction, and
compression; (3) rated horsepower is the power that an engine or motor can
produce efficiently for sustained periods
of time.
Electric motors are capable of surges of power far in excess of their rated
horsepower (see ELECTRIC MOTORS AND
GENERATORS). British automobile engines are classified in rated horsepower,
but their brake horsepower may be four
to six times the rated horsepower. The power output of American automobile
engines is quoted in brake horsepower,
most being rated between 60 and 200 hp.
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