Australia has 415vac 50 Hz 3 phase supply. Motors run at 1480rpm. I need to know the torque available for say 1, 5, 11, 22 and 47kW ac motors. Is there a formula? A web site?

Thanks in advance.

Dave

 

P = Tw
Where P = power (watts)
T = Torque (Nm)
w (omega) = Speed (rad/s)

If you want anything better than that, you need the manufacturer's speed/torque curves.

 

Responding to Dave's query... although you asked for a specific (Au) relationship here are several:

A) Motor Output Rated in kW.
kgf-m = 975 x kW / rpm.
Newton-m = 9,560 x kW / rpm.

B) Motor Output Rated in HP.
lbf-ft = 5,250 x Hp / rpm.
lbf-in = 63,000 x Hp / rpm.

C) Motor output in Metric Hp.
kgf-m = 716 x Cv / rpm.

An aside... Hp is actually based on a geographical location. Anyone know where?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

Gravity is associated with latitude, longitude and elevation (sea level). Am I getting hot?

I also see in the numbers 5252, 30,000 and 2 pye.

Whats the relationship. I've had a look but most sites quote these as constants without justification.

 

Replying to Anonymous' Jul 25, 11:10pm comments... you are right! But before revealing the answer to you I ask for your patience... this is a 3-parter for trivia buffs!

For homework I asked my physics students to research "horsepower!" A popular website was,

http://www.absoluteastronomy.com

Part 1. History (at least the best story)
As part of a marketing ploy to sell his steam engine James Watt compared his invention's output to that of his biggest competitor at the time... the horse! He determined that the typical horse could turn a mill's 12-foot lever-arm 144 times in an hour. Furthermore Watt found
that the horse maintained a force of 180-pounds. Then he calculated the "power" as force times distance divided by time as (180x2x3.14x12)x(144/60).

The resultant, 32,572, was rounded off to 33,000 and was declared the Hp-unit of measurement or 33,000 ft-lb/min.

Part 2. Reconciliation with SI Units.
Let 1-foot = 0.3048 meter; and 1-lbf = ma, then,
1-lb(f) = (1lb)(9.80665m/s^2)(0.45359237 kg/lb), so that,
1-lb(f) = 4.44822 Newtons.

Part 3. Anonymous' Location Answer.
The English were responsible for determining "a", thus it was calculated for the longitude and latitude of Greenwich, England, Lon0° Lat51.48°. Not to be outdone, the French calculated "a" at Lat45°. Unfortunately I don't know the nearest city to Lon0° Lat45°! This led to Cv or "chevaux vapeur" for steam horses. Also known as the metric Hp, the Germans referred to it as PS or"Pferdestarke!"

And now you know... the rest of the story!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

Dear Dr Phil, (no pun intended - well, yes it was!)

HOLD YOUR HORSES!!!!!!!! ha ha!

Apart from the location of where the calculation derived, the location plays no part. What’s the new missing link? I can see a joke about Australia's location coming.

PS. We have enjoyed the physics lesson and we are a little embarrassed I (we) forgot this stuff.

I have stood on the Greenwich line and it was not painful at all. It’s a popular spot to have your photo taken. It didn't improve my memory though.

Thanks again,
Dave Downunder

 

Responding to Dave Downunder's query about the missing link...

"a" @ Lat51.48°N (Greenwich, England) is used for Hp in SI units, while "a" @ Lat45°N (Someplace, France) is used for metric horsepower Ps or Cv. (In fact there is a third designation, Ch.)

Here's a trick to jog your memory... How is the discovery of America (upover) related to the conversion from kW to Hp?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

Dr Phil,

The answer is simple.

Columbus purchased horses from an Irish a guy called Jimmy O’Watt. Unfortunately the horses were of poor quality and the crew of the Santa Maria, once on shore in the Americas felt their worth was about 1/2 their true potential. They likened this situation to living in the 8th century when things must have been really bad. Comments like “I’m going to Kill O’Watt when we get back” and “we should have started this journey 746 not 1492 as we are not getting anywhere with these horses”.

As it happens, to this day we refer the relationship between horse power and kW in this way. Columbus should have started out in the year 746 and the sailers wanting to Kill O’Watt.

Hence.

kW = 746 X Horse power.

I hope that made you laugh

 

Responding to Dave in Australia... tsk, tsk:

An easy way to remember the Watt per Hp constant, 746, is that is half of 1492, the year of Columbus' great discovery.

Well I think of it as a geat discovery! Of course many wish he had gone east instead of west! This comment reminds me of another "direction ploy" designed to make one's life easier:

Back in the '60s NYC's traffic commissioner, Barnes, came up with a plan to eliminate NYC traffic snarls. He simply declared that at 5:00pm, all north-south avenues would become one-way streets... north-bound. Then, traffic would become Westchester's problem!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])