Motor and torque calculations

[claver]

Hi,
I am slightly confused and hope someone can put me straight on this.

Power in W is Shaft torque in Nm * the angular velocity in rad.
So at 195Nm (44lbf) and a shaft speed of 1250rpm I am developing 25619W (25.6kW)

Now when I look at my motor curve …. 44lbf and 1250 rpm …The power curve indicates about 10HP (7.45kW)

Is my motor curve wrong or is it my interpretation of the relationship between Torque and RPM ??

Jan ....

 

[sreid]

You have typed 44 lb-ft twice in your post. 195 N-m is a torque of 144 lb-ft. Is that your problem?

http://www.onlineconversion.com/torque.htm

 

[aviat]

I think you have to divide the product of shaft speed and torque by 5252 or multiply by its recipical 0.00019. The answer then comes out to 10.47kW. (T*RPM)/5252.

 

[IRstuff]

Did you forget to multiply by 3.28 to get ft*lbf? 195N*m=144ft*lbf

TTFN

 

[Skogsgurra]

Sorry to be such a bore. Use SI and forget about all those constants.

1250 RPM = 1250/60 RPS (60 seconds to one minute) and there are 2*PI radians to one revolution. So your speed is 2*PI*1250/60 = 130.8 rad/s

You already have 195 Nm and shaft power is speed times torque or 130.8 * 195 = 25.5 kW, which is wrong.

The 44 lbf (poundfoot? I think poundforce, so the torque arm is missing) translates into 1.36*44 = 59.7 Nm. So your shaft power should be something like 130.8 * 59.7 = 7.81 kW, which agrees quite well with your "about 7.45 kW".

 

[claver]

Thanks everyone !!
Yes my mistake was the "ft/lb" to Nm conversion I did first...

Now it all makes sence ...