In article ,
Al Reid wrote:
"LRod" wrote in message
.. .
On Thu, 17 Mar 2005 12:10:07 -0500, "Al Reid"
wrote:
Good!! Quit while your behind. No need to continue to make a fool
of yourself.
Ummm, I don't think that's pointed where it belongs.
My advice would be to do yourself a favor and stop answering
electrical related
questions. You just continue to embarrass yourself.
You're dead wrong there. Of all the people that post on the wreck, the
one person whose electrical related answers CAN most be depended upon
is Doug.
Frankly, I think you glommed on to a minor nuance (which could easily
have been interepreted other ways) and chose to make some sort of
usenet stand on it. While you may have been technically correct in the
very strictest sense of what YOU were saying, the fact is, that was
not what Doug was saying. And I reread the thread, so I know what I'm
saying. But, in for a penny, in for a pound appears to be your credo,
so, many posts later, here we are.
Ok so you agree that this statement is, indeed correct?
================
So who has a motor drawing over 15A? He said it's a true 1HP motor. 1HP =
apprpox 750 watts = a little over 6A at 120V.
================
YES, that statement is *precisely* correct. When taken _exactly_as_written_.
Notice the period after the word motor.
1 HP is 745.6999+ watts. 745.6999+ watts is 1HP
By "P = I * E" or it's mathematical equivalent "I = P / E"
745.6999+ watts / 120 volts = 6.214158+ amps.
Which *is* accurately described as "a little over 6A".
It does _not_ say that a '1 shaft HP output" electric motor will draw
only around 6 A.
"Power factor" comes into play *only* if (a) you are talking about A,C.
power, *and* (b) 'something' is inducing a phase shift in the current waveform,
relative to the power waveform. Given a purely 'resistive' (or resistive
=equivalent= -- no net capacitance or reactance, and yes a motor _can_ be
designed to that requirement) "power factor" does _not_ need to be considered.
(because it is 'unity' that is, and multiplying or dividing by 1 is 'silly'
"efficiency" comes into play *only* if something is 'transforming' the
energy.
*ALL* of which, you have blithely "assumed" exist in your calculation.
While Doug is correct that 1 HP = approx 750 watts (746), you cannot make
the leap to say that it equates to a little over 6A at 120V. To say that is
to assume that you have a 100% efficient motor. However,
BZZZT! Thank you for playing. *YOU* just made the _assumption_ that the
calculation is to the power throughput of an electric motor.
I = (746 * hp) / (eff * pf * voltage)
Insufficient definition of terms. Particularly as to "what" and "how" the
"HP" is measured. A _draw_ of 746 watts does equate to an _input_ power of
1 HP to whatever device is drawing that 746 watts.
and that also ignores SF.
"Surprise, surprise." Service factor does *not* have a d*mn thing to do
with the 'shaft output' horsepower of an electric motor drawing a given
amount of input power.
SF simply describes the limits of "continuous operation", without overheating.
In the end, the OP stated that his 1HP motor is rated at 12.5 FLA which is
higher then the "little over 6A at 120V."
Now, if Doug had said that 1 theoretical or mechanical HP translates to
little over 6A at 120V, but that the actual current draw will be higher,
dependent on efficiency and power factor OR if he had just acknowledged that
he had not factored that in to his answer, it would have ended after one
reply from Doug. But to start by saying "So who has a motor drawing over 15A?"
and continuing with the statement that a 1 HP motor draws a littlo over 6A is
at best a little deceiving and at worst complete misinformation. I corrected
Doug and he protested.
You read something into his remarks that he did *NOT* actually say.
Yes, his statements were "incomplete", and subject to being mis-read.
"Amplification" of the "incomplete" remarks, to provide the quote missing
unquote information _would_ have been justified.
*CORRECTION* was not called for, however. The 'incomplete' remarks were
_not_ in error.
There are 3 separate sets of "facts" involved, here.
1) what the original poster _intended_ to say,
2) what was actually said
3) what the reader *thought* they read.
#1 is not subject to dispute. *NOBODY* but the original poster knows what
the 'intent' was. Anyone who claims otherwise had better be prepared to
*prove* psychic abilities, or be branded a liar, themselves.
Arguing about #2 requires _careful_ inspection of the words on paper, and
*PARTICULAR*CARE* =not= to invoke any assumptions from #3.
Now, considering that I have a 1930's (!!) handbook that shows the average
efficiency of a 1HP electric motor _in_those_days_ was roughly 82%, and
modern data that indicates the power factor is in the .8-.85 range, means
that a _NINETEEN_THIRTIES_ 1 HP motor should draw about 9.45+ A at 120V AC.
It would seem safe to postulate that motor designs, manufacturing tolerances,
and bearing quality, have improved by a 'non-trivial' amount in the last 70
years, and that 'modern' motor behavior would be somewhat better.
Oh well, life goes on. Doug does normally give out reasonable accurate
information and my statement was made mostly out of frustration.
Lastly, for anyone who is interested here is a link to the rec.woodworking
Electric Motors FAQ.
http://www.faqs.org/faqs/woodworking/motors/
Later
--
Al Reid
And I've had enough of your childishness myself, so I'm through as well.
Good. This took a lot less time than the stoutman/clarke ****fest. Of
course they kept ****ing even after they called "last post" so maybe
this one isn't done yet either.
--
LRod
Master Woodbutcher and seasoned termite
Shamelessly whoring my website since 1999
http://www.woodbutcher.net