# Torque and current relationship

### DC Motor Speed: Voltage and Torque Relationships - Precision Microdrives

Hello friend, The motor you've mentioned is a BLDC motor, not a regular DC Motor. Anyway, the Torque-Current relationship is nearly the same. Can someone please help me understand the relation between volts, amps and torque? I understand with Ohm's law that voltage and current. The relationship between a motor's electrical characteristics and mechanical performance can be calculated as such (note: this is the analysis.

Load adds mechanical resistance. The motor starts to consume more current to overcome this resistance and the speed decreases.

## Understanding DC Motors

If you increase the load at some point motor stops this is called stall. When it occurs the torque is at maximum and it is called stall torque. While it is hard to measure stall torque without special tools you can find this value by plotting speed-torque graph.

You need to take at least two measurements with different loads to find the stall torque. How accurate is the torque calculation?

While voltage, current and speed could be accurately measured, efficiency of the motor may not be correct. It depends on the accuracy of your assembly, sensor position, friction, alignment of the motor and generator axles etc. If you want to get meaningful numbers you might use a second generator kit as explained in Torque and Efficiency Calculation section.

### voltage, current, torque and speed in DC motors - Electrical Engineering Stack Exchange

Speed, torque, power and efficiency of the motors are not constant values. Usually the manufacturer provides the following data in a table like this one sample data from one of the motors used in generator kit: Also the manufacturers usually provide power curves for the motor at nominal voltage: These curves are generated by plotting motor speed, consumed current, and efficiency as functions of the motor torque.

Sometimes there might be also a curve representing mechanical output power. As you can see from the graph speed and current are linear functions of torque so you might need only two measurements to draw these graphs. This is usually true, but not necessarily always true.

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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.

This is assuming of course the DC motor doesn't burn up, reach a state which violates this simplistic ideal motor model, etc. However, between different motors it's impossible to tell how two motors will perform compared to each other based only on the voltage rating.