Very simple name-plate question

[tim9000]

If a motor is such-and-such Hp or kW, is that the Output power, or the Input power?

 

[davenn]

from memory its the output power as measured at the driveshaft
Dave

 

[tim9000]

from memory its the output power as measured at the driveshaft
Dave

Huh, ok that's a surprise.

It's funny that I'm doing a practice question where the input power as calculated from the output power + loss, is different from the rated input current multiplied by rated inut voltage.
Just thought I'd throw that in as an oddity, I don't understand how.

anyway, cheers.

 

[davenn]

Just thought I'd throw that in as an oddity, I don't understand how.

why do you think it's odd?

if they wanted to that they could take the BTU rating of the fuel, work out the power generated by the engine, subtract the losses and get an output power
in the specs listing, its a lot easier just to state it's output

Ohh and I forgot to add in the first post. the power out will usually be stated for a given rpm

 

[davenn]

some reading for you ...

https://en.wikipedia.org/wiki/Horsepower

a way down that page ...

Also, with a chassis dynamometer or rolling road, power output is measured at the driving wheels. This accounts for energy or power loss through the drive train inefficiencies and weight thereof as well as gravitational force placed upon components therein.

In general:

Nominal or rated horsepower is derived from the size of the engine and the piston speed and is only accurate at a pressure of 48 kPa (7 psi).[23][clarification needed]
Indicated or gross horsepower (theoretical capability of the engine) [ PLAN/ 33000]
minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.), equals
Brake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft)
minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equals
Shaft horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system)
minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present), equals
Effective, True (thp) or commonly referred to as wheel horsepower (whp)

you can see my driveshaft rating in there amongst other styles ... Brake HP is the other one I'm commonly familiar with

1HP = 745.7 WattsDave

 

[tim9000]

That is a good point.

why do you think it's odd?

What I think is odd is that I'd have thought that if you multiplied the terminal voltage by the current going into the motor, that, that'd be the total input power. However in my qustion it turned out that the output power + loss' were greater than that, hence the input was greater than VI at the terminal.

Cheers

 

[meBigGuy]

Looking at the following arbitrary motor specs

http://www.automationdirect.com/static/specs/ironhorsesprs.pdf

the 1 hp motor draws 13.6A at 115V at Full Load, which is 1564 watts. It is then listed on the second page at 68% F.L efficiency and 0.66 F.L. power factor.

Doesn't the nameplate have the current?

 

[CWatters]

Huh, ok that's a surprise.

It's funny that I'm doing a practice question...

Can you post the question word for word. In other sections of the forum (eg the homework section) this is a rule because it frequently turns out that the OP has misunderstood or misinterpreted the question.