[USMA:32891] RE: horsepower

[Daniel]

Title: Message

I don't think they mean peak in the sense of the "peak" of the sine wave as in peak voltage or current vs. RMS.  They may mean peak as in short duration.  Some devices are designed to provide extra ability for short durations.    The peak power may be obtained when the motor is started as the current at that point is very high, but due to the short duration of the peak, the circuits do not blow because fusing is designed to handle surges of currents for a short time.   I also find that electrical peak power would be small as a motor is an inductive device and the voltage and current are out of phase, thus the concept of power factor.  If the voltage is at it's peak the current will not be at its peak as with a resistive load.  Therefore you can not just multiply the voltage and current together in reactive circuits to get the power or if the power is known, to divide it by the voltage to obtain the current.  You have to account for the phase shift.   Do you happen to know what current the vacuum clean draws under normal operation?  Do you know the power factor?   I would suggest that you re-contact Shop-Vac and this time insist on speaking to an engineer and asking him/her how they determine peak power.  Without really knowing, everyone is just guessing.   Dan         ----- Original Message ----- From: Nat Hager III To: U.S. Metric Association Sent: Monday, 2005-05-23 20:28 Subject: [USMA:32880] RE: horsepower "6 peak" hp might mean divide by sqrt(2) to get RMS, but that doesn't buy you much.    BTW, could anyone explain the reason for 3-phase circuits in power transmission (off-list if necessary).  I should know that, but don't!   Nat -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Carleton MacDonald Sent: Saturday, 2005 May 21 0:01 To: U.S. Metric Association Subject: [USMA:32873] RE: horsepower I�ve always thought it amusing how some appliance manufacturers have outlandish �horsepower� claims.   A shop vacuum I bought proclaimed �6 peak horsepower!�  6 hp x 0.746 = 4.48 kW / 117 volts = 38.29 amperes = no 117 volt circuit in my house could even begin to handle that.  (And most motors over 5 �hp� are polyphase anyway.  They don�t wire residences with  277/480 volt 3-phase circuits in my neighborhood.)   When I wrote to Shop-Vac about this they were less than cordial.   I must have insulted the marketeers.   Geez.   Carleton   From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Nat Hager III Sent: Friday, May 20, 2005 11:10 To: U.S. Metric Association Subject: [USMA:32870] horsepower   The only thing you need to know about horsepower is how to mulitply by 0.75 to get kW.  The rest is easy...   Nat   2005 CanWest Interactive, a division of CanWest Global Communications Corp. All Rights Reserved Times Colonist (Victoria, British Columbia) May 20, 2005 Friday Final Edition SECTION: DRIVING; Pg. C10 LENGTH: 614 words HEADLINE: Figuring horsepower a confusing process BYLINE: Graeme Fletcher, For CanWest News Service BODY: The lowly horsepower is used to rate everything from vacuum cleaners and chainsaws to lawn mowers, snow blowers and the automobile parked in your driveway. Simply stated, horsepower defines and quantifies the rate at which an engine can perform mechanical work. James Watt -- the very man whose name is used to define the brightness of a light bulb -- originally coined the term. History shows that Watt was working with horses in a coal mine when he decided to evaluate the power -- or work -- one of these beasts could produce. Watt discovered the average horse could perform 22,000 foot-pounds of work in one minute. Then, for some unexplained reason, he arbitrarily raised this number by 50 per cent to establish the horsepower rating used today. Thanks to Watt's work, we now know that one horsepower is defined as the ability to produce 33,000 foot-pounds of work every minute. To arrive at this number, vehicle manufacturers use a dynamometer -- or rolling road -- to measure power production. However, herein lies the rub. Dynamometers actually measure torque (twisting power) in pound-feet, so manufacturers convert this number to horsepower by multiplying it by engine speed (r.p.m.) and then dividing it by 5,252. It should be simple. However, some confusion creeps in because not all automakers use the same format to arrive at an engine's optimal output. Under the metric system, one horsepower is defined as 4,500 kilogram-metres per minute. This is the equivalent of 32,549 foot-pounds per minute, meaning each metric horse is only 0.986 the size of an Imperial one. It's a confusing situation. Given that horsepower is the main number used by most to judge the relative worth of an engine, instances of "misstating" output are common. Mazda overstated the 2001 Miata's horsepower by eight per cent -- a small amount when all is said and done, but an overestimation nonetheless. Mazda Canada gave Miata owners the option of selling their cars back to the company or keeping the cars and taking free factory-scheduled maintenance for the length of the three-year warranty, plus compensation of $500. While only 26 owners opted to have their vehicles repurchased -- insignificant in the realm of things -- Mazda ended up with a red face and a dent in its credibility. Using metric horsepower without specifying it is just as wrong. For example, the original Honda S2000 blew its 240-horsepower trumpet long and loud. However, as the 2.0-litre four-cylinder engine pushed metric ponies, it actually only delivered 236.7 horsepower (the number quoted in Europe). I guess saying an engine pushes 118.35 ponies per litre is not quite as sexy (or as nicely rounded) as 120 horsepower per litre. The flip side is understating the available power. Anyone who drove an early '90s Mazda MX-6 or Ford Probe GT with the 2.2-litre turbocharged engine will remember what it felt like to have bionic stallions under the hood. While the car was officially rated at 145 horsepower and 190 pound-feet of torque, the torque steer generated when the gas pedal was hammered off the line, the kick in the pants that ensued after muscling the wheel to the straight-ahead position and thrashing on up through the gears, said there was something rather wrong. Nobody will say (let alone admit) why full credit for the oomph was not taken, but it was rumoured to be all about keeping insurance rates sane. Sadly, the SAE's new standard for arriving at the actual output of an engine is only voluntary at the present time. If all manufacturers used the new standardized test to arrive at an engine's actual output, comparing performance numbers and specs would be so much easier -- apples to apples as it were. 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