# Torque current and voltage relationship

### Torque in relationship to Voltage - Electrical Engineering Stack Exchange

Torque is related to current, so you can use the winding resistance to have a relation between voltage and torque. You can review the mathematical model (for a. And when supply voltage is constant, speed is inversely proportional to the load This can be demonstrated by the DC motor torque equation. Relation between motor's torque/speed and its voltage/current 23 Jan The torque of a motor is proportional to the current flowing through it (τ ∝ i).

The torque required to turn a variable torque load goes up at a rate of the speed squared.

### Relation between motor's torque/speed and its voltage/current. - Doswa

Since power is speed times torque, the power required to turn such a load goes up at a rate of the speed cubed. This has a huge effect on the torque required and good example is this: Constant power The required torque is inversely proportional to the speed.

An example would be a grinding wheel. The problem with small hobby motors is that the specifications generally do not provide a maximum power rating.

Without a power rating, it is difficult to predict what the motor life will be for a given set of conditions.

Small hobby PM motors are high speed with corresponding high frictional losses - which cause most users to misinterpret what they see with regard to the three basic physical relationships that exist stated in post 2 in a PM DC motor. Ultimately, is the motor selected capable of running at the required torque? How far away from the stall torque is that rating?

I'm not knowledgable there so I leave that to others to comment. Lastly, there is the issue of available current.

## Calculations

Can your power supply provide what the motor requires to produce the desired torque? If not, the speed falls off since the torque is being limited by way of the supply current. That's the easiest of the lot to solve ;- As for some of the other material posted here, it is misleading at best. Quote What is missing from that is the role of voltage in "forcing" the current through the motor.

It is missing from the discussion because it does not exist.

## Relation between motor's torque/speed and its voltage/current. :: 23 Jan 2010

The voltage applied has zero effect on the available torque. The back-emf models the voltage generated by the moving electric current in the magnetic field basically a DC electric motor can function as a generator.

It's also possible to model the inherent inductance of the motor by adding an inductor in series, however for the most part I've ignored this and assumed the motor is at quasi steady state electrically, or the motor's time response is dominated by the time response of the mechanical systems instead of the time response of the electrical systems.

This is usually true, but not necessarily always true. The generator produces a back EMF proportional to speed of the motor: The current flowing through the motor can then be calculated: The torque generated by the motor is proportional to the amount of current flowing through the motor: Also, at the no load speed the motor has no torque and no current flowing through it. When does the motor produce the most power?

Well, power can be calculated one of two ways: So all things considered, how does the motor voltage stack up? For the same motor, ideally if you apply double the voltage you'll double the no-load speed, double the torque, and quadruple the power.