# Motor power and current relationship status

"With a motor with an output of 50 HP, to convert the HP output into Watts is: so for operating motor in no load condition less power will require as current. If the question is about the relationship between induction motor current and shaft torque Small differences in power factor and motor efficien. In a no-load condition the only torque that is needed is enough to overcome bearing friction and. In general, to get the same power out of a motor at half the voltage, the current must double to get double the torque to ultimately provide the.

It could be also converted further to still common gram force centimeters g-cm by multiplying the result by In our example input electrical power of the motor is 0. Motor torque changes with the speed.

### Motor Voltage, Amps and Torque Relationship

At no load you have maximum speed and zero torque. Load adds mechanical resistance. The motor starts to consume more current to overcome this resistance and the speed decreases. 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.

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: 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?

## Calculations

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.

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.

### D.C. Motor Torque/Speed Curve TutorialUnderstanding Motor Characteristics

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. The voltage applied has zero effect on the available torque. A motor is not a resistor, amps are in no way proportional to applied volts.

Quote If you have a specific motor and if you reduce the voltage from 6v to 3v then you CANNOT get the same current in the motor, never mind getting double the current.