powerstepper motorstepper-driver
We are using a stepper motor with a Current rating of 0.65A and rated voltage of 4.55V.
We are using a 12v power supply. The current driver chip is limited to supply 0.7A.
Would the power of the motor be equal to Supply Voltage * Rated Current. Or will it be equal to motor rated voltage * rated Current.
What kind of steppr driver are you using? Setting the current limit with the power supply is a bad idea - it's not designed to do that, unless you are using a lab supply! It would be a beter idea to invest in a proper chopper driver that uses a PWM drive on top of the actual stepping to set the current through the coils, and then use a properly-sized power supply. There should be a way to set the drive current with either a software seting or a trimmer pot. At any rate, the motor torque is determined by the coil current, and you will need to turn it up until it doesn't skip steps. At high currents you may also need to cool the motor. The drive transistors will certainly need a good heatsink, but they should disspate less heat than the motor.
Edit: Chris remided me of another very important advantage of chopper controllers: driving the inductive motor windings. Inductive coils will try to resist changes in current flow. As a result, when the motor steps, the coil current takes some time to 'ramp up'. If you want to step very quickly, you need to use a high drive voltage to so that the coil currents will ramp up faster. This means that you need to use regulators on each coil. Chopper controllers do this for you, and all you need to do is set the desired max coil current. Chopper controllers can generally also microstep the motors, interpolating the coil currents to hold the rotor between steps. If you use the proper controllers, then you can get away with cranking the supply voltage up to 24 or even 36 volts for better performance.
The DRV8818 can be current limited to whatever value you choose (within reason) by altering two resistors per motor: -
Look at IsenA and IsenB in the data sheet - top of page 11: -
Best Answer
The power absorbed by stepper motors varies depending on the state of the motor and driver.
When holding position using full step or half step, the power will be governed by:
\$P = I^2R * Coils\$
where
If you are holding a micro-stepped position then it gets more complicated since you need to calculate the impedance of the coils at the PWM frequencies and do the appropriate math for whatever coils are on and off with the duty cycle involved.
Similarly, while being driven at some speed, the impedance of the coils at the applied step rate also needs to be calculated.
At higher speeds where the step time is less than the time constant of the coils the calculation gets more complicated and the power absorbed actually drops off markedly as it becomes harder and harder to establish the drive current.