re: HP rating (more) my formulas' better'n yers???

Hi all,

I expected this... Now, I have to ask. Did any one (replying)besides
Terry L R actually READ the WHOLE post and scan the link???

The electrical guys and old timers will say, a horsepower AINT what
it used to be, and they'll pull out the 746 watts equation to prove
their point... Who DERIVED this definition of horsepower? And when?

We KNOW who, and when the 550 ft.lbs./second was DERIVED! We also
know that 550 ft.lbs./second can be achieved in MANY ways. The fact
that some of you seem not to like this DOES NOT change the FACTS!

Please understand that I too, can see and feel the difference in
performance between my old open frame induction-repulsion 2HP motor
and the modern 5HP TEFC cap start motor which replaced it on a big
bandsaw... The old TWO HP was better. Had I known, I would have re-
wound it and kept it(and this is the type of motor you are saying
is "HP correct")But OSHA didn't like it much :-(

But the issue here is facts, not feelings. And the math backs it up!
Mariss explained a very similar situation awhile back in the thread
re size 42 motors with the gecko drives (torque curve output did not
match torque curve NEED, and therefore power output was limited)

(snips, inserts below)

Terry A wrote:

>Perhaps equipment is now rated against Sea Horses.

Terry,

I enjoyed the humor of the message. Can a horse 'run' a router bit?
At 20k RPM? When I finish a day of work with my power tools, how many
horses' power have I used? Should I use James Watts' equation to
determine if the ratings ARE overrated? 550 ft. lbs./second easily
and directly converts to rotationally applied torque. There is a
DIRECT correlation between the two. WHAT is the correlation between
550 ft. lbs./second and 746 WATTS!?

Jon E wrote:

>Not so! The reason is that the real horse power definition is based
>on a horse being able to produce this power output for a full 8 hour
>day without any over-taxing of the horse, such that he can come out
>and do it again the next day.

And later added:

>Well, I don't think precision (related to horses) is very high here.
>But, the HP was supposed to be what a quarter horse (NOT draft
>horse, Percheron, Belgian, etc. even bigger than Clydesdales) could
>produce for a full 8-hour or so shift, and be happy to come back and
>do it the next day. In other words, kind of a standard work day for
>such a working horse.

Jon,

This is interesting info. Could you provide a link or reference to
back up your assertion? I've never seen any reference to the type of
horse Watt used, or the length of time the formula refers to. I HAVE
always ASSUMED it was a standard type horse, and NOT a Draft horse
(my grandfather ran a team of Belgians/Percherons on a 'milk' route).
Now that I think about it tho, why wouldn't he(Watt) consider a draft
horse THE standard? They were/are the 'pulling' horses! And the 8
hour shift is MUCH more recent than Watt!

>These inflated horsepower ratings are based on the current
>draw during motor starting, and would cause the motor to burn out
>within one minute if the condition persisted.

Nope, do the math with ft. lbs., NOT watts. On a Dyno. They're not
lying, according to Watts' formula!

>Also, if you figure out how much power you can get out of a 120 V
>15A power outlet, you will have trouble delivering even 2 full

horsepower continuously from a practical motor with that available
line power. How a vacuum can carry a 6 Hp rating when it runs at
about 10 Amps on 120V is obviously a lie. If the power input is
clearly less than 2 electrical HP, you can't get 6 HP out of it.

Jon,

One word above 'saves' you. When you state 'electrical' HP, you
clarify that you are speaking from the standpoint of the 746 watt=one
HP position. From that assumption, your words are correct. However, I
can easily provide the equivalent of 1100 ft. lbs./second
continuously from a motor on a 15A, 120V circuit...

Again, I'm not saying I LIKE the changed way the term 'horsepower' is
being used; only defending its' mathematical correct-ness. I have
been using tools a long time and there is a difference, as I stated
above.

Smoke wrote:

>I'm with you there Jon....you'd need at least a 40 Amp breaker to
>provide 6 HP.

Sorry Smoke, It aint so! What IS true is that a typical 1725/3450 rpm
6HP induction motors WILL require a 40A+ breaker.

>As for the HP formula developed by Watt...IMO that was one of the
>stupidest formulas ever developed.

It may well be. But we have LOTS of 'stupid' standards... The inch,
the foot, the meter, the quart, the liter... The ampere... The ohm...
ALL ARBITRARILY derived.

>How big and what kind of draft horse was used...large/small
>Clydesdale...Percheron...or ???
>Did he make that horse move 33000 pounds per foot per minute all day
>long or just for a limited time...like say for only a minute?
>How many times did he perform the test? How many horses did he use?
>ETC.

I'll wait for the references from Jon E (or someone else). I'm
interested in this too!

>Not only did he develop his formula based on an arbitrary horse
>selection, he didn't even have enough sense to use more manageable
>figures...like say 500 pounds per sec or 30000 pounds per
>minute...which would make calculations a whole lot simpler.

I have an interesting book on process control and optomisation which
has a chapter about shoveling coal by hand. In it, a factory
using 'scientific' measurements determined that the best size 'load'
for a shovel operator working all day(10 hours) was 8 lbs. To apply
your logic, they "should" have used 10 lbs. so the math was easier...
BTW, they then CUT the shovel blade size so that the 8 lbs. load
became 'typical', and watched production soar, and worker injury
claims drop!

>As for lifting 33000 pounds....any horse can do that...just use
>enough rope/cable and pulleys. Doing it so as to move the load.

Of course. But the use of mechanical advantages is CLEARLY NOT part
of Watts equation! Or is it? I've only ever seen the figures in
textbooks drawn WITHOUT extra pulleys. But, I WASN'T there with Mr.
Watt! Let's see those references!

<snip> Based on "instantaneous" loads, it can be done. What is

>necessary is to determine at what point (in time) the resistance in
>the motor is at it's lowest point. At that particular instant, apply
>the current at it's maximum voltage (based on the sine wave of the
>applied voltage). It's absolutely amazing how much useable
>values can be distorted in this manner!
>Smoke

Once again, the 'electrical HP' is used. True as written... But as
stated above in response to Jon E, NOT necessary to distort! Just use
the 'mechanical HP' definition.

Jerry Kimberlin wrote (in response to Smoke):

>>Smoke wrote:
>><snip> How big and what kind of draft horse was used...large/small
>> Clydesdale...Percheron...or ???

>I'm nearly sure that the concept is an "average" of what was
>experienced in those days. Probably used to compare things for
>equivalency in order to negotiate trading.

>It is true that any horse can lift any weight given enough rope
>and sheeves. Of course, there comes a time when the horse is
>primarily overcoming the friction of the multiplication device
>and not lifting anything fast enough to measure in a reasonable
>length of time :-).
>JerryK

Jerry,
Thank you for your input. Although I agree with your statements, this
thread has shown me that I really DON'T KNOW whether it was all day
or not? Also whether mech. advantage was used? And draft horse or
not? It could easily be argued (in each case) that either makes sense
(in the absense of some 'eyewitness' writing or pictures).


Terry LR wrote:

>horsepower is also defined as:
>hp = torque X rpm X 1/5252
>therefore 1 hp means that torque X rpm equals
>5252 (ft-lbs) X rev/min.

>also air compressors are normally rated by the
>compressor and not the driving engine or electrical
>motor. a compressor is basically an engine.
>by changing the pulley on a compressor the
>torque can be changed. changing torque and keeping
>rpms the same will cause hp to change accordingly.
>
>also a blower/vacuum is not rating the drive
>motor but rather the fan itself. again the torque
>X rpms quanity.
>
>at 1720 rpm only 3.054 ft-lbs torque is needed to
>have 1 hp rating.
>
>using a dynamonmeter the hp - torque plots may be
>obtained over a range of rpm.

Terry LR,

Thank you for the additional points. You have clarified what I was
saying.

Thank you all for the feedback. I love this list!

Hope this helps.

Ballendo