"Robert Bonomi" wrote in message
...
In article ,
================
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.
Context. It all must be read in context. They were discussing motors and
current draw 120V vs. 220V. The entire context was about motors. He chides
toller for suggesting that a 1 HP motor would draw 15 A and then attempts to
prove him wrong by doing a calculation. In that context, "I=P/E" is
invalid. We were not discussing the current draw of a resistance heater on
120 vs. 220.
"Power factor" comes into play *only* if (a) you are talking about A,C.
....which we were.
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.
The discussion was about AC motors. What else can one assume in a
discussion about whether to run a motor on 120 vs 220? Assume we are
discussing electric heaters? Come on, be serious.
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.
It was and is a correct assumption in the context of the discussion.
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.
Once again, it is correct in the context of the discussion.
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.
It will effect the current draw of the motor and whether it can ever draw
more than 15 amps.
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.
My mistake for reading his comments in context.
Yes, his statements were "incomplete", and subject to being mis-read.
Then he made them in the context of motors and therefore efficiency and
power factor cannot be excluded, unless one is attempting to be misleading.
"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.
And of course, carfull inspection of the words on paper within the context
of the paragraph and the overall discussion.
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.
The only thing one can go by is nameplate data. Small motors tend to be
less efficient than large motors. DAGS on motor data and you will find that
most 1 HP motors fall in the range of 10 to 13 FLA. Someone just posted
that his is shown as 14FLA. The nameplate data from the 1 HP motor that
started this entire thread stated 12.5 FLA. As plain as I can state it, in
the context of the discussion, a 1 horsepower will not draw ~6a. You can
argue Ohms law all you want, but in the context given the statement was
either intentionally misleading or woefully out of context. If you go back
and read it in context, you will have to agree.
In the end, I suspect that we all know the equations and the theory and how
to apply them. This whole thing comes down to being willing to accept the
context in which the remarks were made. I am sure you would not let me get
away with stating or implying that a 1HP = approx 750 watts = a little over
6A at 120V within a discussion of whether I should convert my motor to 220V
or leave it on 120V. You would be one of the first to point out that I had
neglected to take into account efficiency and power factor and that in
reality, the current draw would be higher.
This is the end of the line for me in this thread. The horse is beat and
the OP has already started another thread wherein he is still trying to
decide whether he should convert his 12.5 A 1 HP motor to 220VAC.
Good night.
--
Al Reid