Two Speed Variable Torque Motors
Information Compiled By: Michael Aschbacher
A motor that is commonly found is industry is a two speed, variable torque motor. This motor has some very specific traits, regarding energy consumption, power produced, and application. In this paper, I will try to generally cover two speed variable torque motors, though there are many different flavors out there.
Let’s cover the first part: two speed. Now, there are many different kinds of motors that allow for two speeds, or more, through terms of windings, transmissions, power consumption, ect. Most two speed variable motors have a single winding, and use an increase of electricity to increase speed. There are a few two winding motors, but the same rule of more electricity - faster speed still applies. Also, these motors run on AC, not DC.
Possibly the most unique feature of this motor type is the variable torque. Let’s take two examples of motors with two speeds to show the difference.
Constant Torque | RPM | 900 | 1800 | Variable Torque | RPM | 900 | 1800 |
| Torque (in Ft. Lbs) | 14.5 | 14.5 | | Torque (in Ft. Lbs) | 14.5 | 29 |
| HP | 2.5 | 5 | | HP | 2.5 | 10 |
So, by looking at the tables above, we can see the direct comparison between a constant and variable torque motor setup. As the speed on variable torque motor increases, so does the torque, multiplying the HP. Normally, the torque increases relative to the speed increase, but there are some that have other speed to torque ratios.
Lastly, are the applications that variable torque motors are used for. Primarily, these are used in situations where more power is needed with higher speeds, such as fans, pumps, and blowers. In the example of a fan, higher torque is needed, because as it tries to push more air, it needs more power, not just speed. A comparison would be to a conveyor belt, where no matter what speed it’s going, it’s going to be carrying the same load, thus not needing increased torque. This...