## Definition of Torque vs Power

## Definition of Torque vs Power

(OP)

I am struggling with the meaning of Torque. I know the equation of HP=Torque*rpm/constant. It is when I apply that to a gear box or a motor, I get confused.

If a gear box is rated for a certain torque, what happens when I speed up the output shaft by changing the gear ratio. Is the torque rating of the gear box changed? Or is there just a new calculation using the above equation and since I have sped the box up, I can now put a larger motor on the box.

For my particular case, I have a adjustable torque limiting coupling between the motor and the gear box. I have sped up the output shaft from 300 to 450 rpm and I am changing the motor from 150 HP to 250 HP. Do I need to increase the torque setting on the coupling? By what percent?

Thanks,

If a gear box is rated for a certain torque, what happens when I speed up the output shaft by changing the gear ratio. Is the torque rating of the gear box changed? Or is there just a new calculation using the above equation and since I have sped the box up, I can now put a larger motor on the box.

For my particular case, I have a adjustable torque limiting coupling between the motor and the gear box. I have sped up the output shaft from 300 to 450 rpm and I am changing the motor from 150 HP to 250 HP. Do I need to increase the torque setting on the coupling? By what percent?

Thanks,

Bob Sander

robert.sander@solvay.com

## RE: Definition of Torque vs Power

The equation you need is P=Tw where:

P = Power (kW)

T = Torque (Nm)

w = Speed (rad/sec)

You know the output speed and the power generated, and therefore you can find the torque required.

I hope this is what you are looking for?

BandH

## RE: Definition of Torque vs Power

Nigel Waterhouse

n_a_waterhouse@hotmail.com

A licensed aircraft mechanic and graduate engineer. Attended university in England and graduated in 1996. Currenty,living in British Columbia,Canada, working as a design engineer responsible for aircraft mods and STC's.

## RE: Definition of Torque vs Power

The torque rating on the gear box is to avoid breaking the gear box. This has some safety factor in it but if you are increasing the speed and the Power, I would think twice.

Edson Campos

edsoncampos@earthlink.net

## RE: Definition of Torque vs Power

The Gear box is always rated for constant torque. When you speed up the output shaft with the same motor then you are decreasing the torque so in order to speed up and obtain the same torque you need to use a higher hp rated motor. This is what you propose doing when you say you are speeding up the output shaft from 300 to 450 rpm and changing the motor from 150hp to 250hp. However, check your calculations using the same equation mentioned by you and you will find that to maintain the same torque at 450 rpm you need an input of 225hp and not 250hp. As far as the torque setting on the coupling is concerned, you need not reset the coupling since the coupling is toque rated and will disconnect whenever the torque increases.

I will be pleased to get a feed back from you.

Thanks.

Najeeb.

mnajeebuddin@yahoo.com