# constant torque

#### wes

Joined Aug 24, 2007
242
are there any motors that are able to maintain a constant torque no matter the rpm . so say it runs at 5000 rpm no load and 5000 rpms under load because the torque doesnt decrease with speed increase or decrease and pulls the same amount of power

#### beenthere

Joined Apr 20, 2004
15,819
Read up on pulse width modulation. That is the technique used to maintain nearly constant torque over the whole range of DC motor speed.

AC motors can be controlled over a range of speeds with nearly constant torque using a variable frequency drive to essentially make a simulated AC waveform.

#### Ron H

Joined Apr 14, 2005
7,014
are there any motors that are able to maintain a constant torque no matter the rpm . so say it runs at 5000 rpm no load and 5000 rpms under load because the torque doesnt decrease with speed increase or decrease and pulls the same amount of power
Power output is defined as torque times rotational speed. Since input power is proportional to output power, then at fixed RPM, the input power will change as the load changes.

#### h.d

Joined Oct 22, 2007
150
are there any motors that are able to maintain a constant torque no matter the rpm . so say it runs at 5000 rpm no load and 5000 rpms under load because the torque doesnt decrease with speed increase or decrease and pulls the same amount of power
you ask about motor with constant torque at variable speed or constant speed at variable torque?
if you mean constant speed (5000rpm at noload and 5000 rpm at loaded)
you should use syncronous motor which is AC-motor

#### shankbond

Joined Nov 4, 2007
53
you ask about motor with constant torque at variable speed or constant speed at variable torque?
if you mean constant speed (5000rpm at noload and 5000 rpm at loaded)
you should use syncronous motor which is AC-motor
my friend i believe that ,if there is load on synchronous motor then it draws more power,which is not desired .

#### scubasteve_911

Joined Dec 27, 2007
1,203
I'm confused... Do you expect mechanical power for free? Of course the electrical power demand will increase! Synchronous AC motors do run at a fixed speed by design and will try its best to maintain it under load,.

Steve

#### wes

Joined Aug 24, 2007
242
alright thx for all the input

#### Papabravo

Joined Feb 24, 2006
19,836
Every set of DC motor performance curves shows the torque going to zero at some speed. This is entirely different from the minimal torque required to keep a motor going at a constant speed within its range.