[USMA:15769] Re: IEEE per 2001-10

Sat, 20 Oct 2001 21:34:53 -0700

2001-10-21
 
Does your household shop vacuum actually work at 240 V?  Is this a portable type or one of those mounted to a wall in the basement with hose outlets located in different rooms of the house?  I would guess the later, because I know of no portable household appliance designed to run at 240 V in the US.  Even heating devices, such as portable space heaters, hair dryers, etc. are designed to run at 120 V, 12.5 A (1500 W) maximum.  This assures the normal 15 A branch and socket are not overloaded. 
 
Even so, that "peak horsepower" must be the "power" the motor draws under locked rotor conditions.  The maximum current times the voltage applied divided by 750 and rounded.  I just wonder for how long that motor can provide that peak power before it attempts to burn the house down. 
 
I hope that thing has plenty of fuse protection.
 
John
 
P.S.  Did you intend for Herr Schwartz to receive your response?  Well, he did, since you cc'd him.
----- Original Message -----
Sent: Saturday, 2001-10-20 23:14
Subject: [USMA:15766] Re: IEEE per 2001-10

In a message dated 2001-10-20 11:11:46 Eastern Daylight Time, [EMAIL PROTECTED] writes:


The resistance among mechanical engineers to drop the horsepower most likely
has a lot to do with the magnitude of numbers.  A 5000 HP motor, depending
on how much over design there is in it, can be "rated" in kilowatts anywhere
from 3 750 to 4 000 kW.  In these cases, the numbers can be rescaled to 3.75
and 4 MW.

The instinct of a typical mechanical engineer is to just convert the numbers
with a calculator and let the power in watts come out where it does.  But,
you are stuck with a "funny numbers" that twist the tongue.  Also, powers in
watts tend to be numerically less than their equivalent in horsepowers, thus
the motor doesn't seem to be as impressive.  Mechanical engineers like big
numbers.   It somehow must make up for something else that is lacking.  As
for the power efficiency, the mechanical engineer doesn't care.  He turns
that over to the electrical engineer to convert the hp's to watts and see
how much electrical power is required.  As long as the motor does its job,
they don't care.


And then you get the idiotic claims on certain household products where, for example, a shop vacuum says "6.0 peak HP" which would equate to about 4.5 kilowatts which, in turn, would imply its own dedicated 30 amp, 240 volt circuit!  Actual wattage on the one I have (and the one that makes this claim) is about 900 watts which would be about 1.2 HP.  (The above assumes no losses in conversion of electricity to mechanical motion, which of course isn't the case.)

Carleton

Reply via email to