DRV8825 understanding and Thermal Issue

Hi Pavan,

Pavan Panchamukhi said:

1. I am working on various frequency but stepper motor supports only certain frequency at which the motor rotates. Can you please let us know what is the maximum frequency the motor can run. 

Motor Spec Below:  catalog.orientalmotor.com/.../pk244pda-p5

This is really a question for the motor manufacturer. There are a few items to note. The maximum starting speed is ~120 RPM. This is 2000 steps/sec in full step mode @ 0.36steps/full step

Pavan Panchamukhi said:

2. Also, when the Motor is connected and when we try to run the motor and Driver IC gets heated up. What is the solution to avoid thermal dissipation.

Please try fast decay and report the results.

Pavan Panchamukhi said:

3.We are trying to run motor at 100 RPM by giving 1.6Khz full step, But across coil we are observing 13Khz in spite of giving full stepping. We have set the Vref pin to 2.4V with Ichop current set to 1.45A. Is this ok for attached motor spec ?

A chop current of 1.45A is ok for the motor.

Pavan Panchamukhi said:

3. We are providing the Ichop of 1.4A but in ammeter its showing 0.5A which is contradictory.  Is this the intend way to run. 

There are several issues with using an ammeter. First is that the ammeter is averaging the current. Second is the placement of the ammeter. If in series with the power supply, you are reading the average current required by the system. The local bulk capacitor are providing the current to the windings.

A current probe is usually the best method of determining the current in each winding. If that is not available, the next best approach is the measure the voltage across the sense resistor and capture voltage on the xOUT1/2 pins at the same time. The xOUT1/2 voltage provides the decay information. 

Hi

Please find the attached current waveform image . We are still observing motor getting heated. Can you please let us know how to overcome the issue ?

Pls let us know if you need any further data / image.

Hi Pavan,

Do you still have the IFS set to 1.45A? The current waveform looks lower than expected.
What microstep rate are you using?

The motor will heat up due to the current through the windings. There is approximately 1.5W generated in the motor based on the image. RMS current = .707 * 1A peak = .707. I2R = .75W/winding * 2 windings = 1.5W

The motor specification does not detail the expected temperature rise.

Hi Rick Duncan


I have set the chopping current to 1A.

We have set the micro-stepping rate to 1/4 micorstep.

as per motor spec it is capable of dissipating 6.24W as below calulation
P = V * I = 2.14 * 1.5 = 3.21W/winding so motoris capable of dissipating 6.24W. Am i correct in saying ? But still motor is getting heated. Pls help ?

Hi Pavan,

The temperature of stepper motors increase as the motor is operated. The current waveform appears to be normal.

It is suggested to contact the motor manufacturer. In the datasheet, there is a note stating

"Temperature rise of the windings is 176°F (80°C) or less measured by the change resistance method when equipped with an aluminum heat sink of 6.89 x 6.89 in., 0.20 in., thick. (at rated voltage, at standstill, 2 phases energized)"

Do you have the aluminum heat sink mounted? If not, it is suggested to contact the motor manufacturer to determine the temperature increase in the motor.

Hi

Can we connect DC Motor to DRV8825 Driver IC  ? 

DC Motor Electrical Spec 

VCC = 5V

Winding Res = 1.5Ohms

Thanks

Pavaman. P

Hi Pavan,

The DRV8825 is designed to operate a stepper motor. A DC motor can be connected but there are many constraints. The top three are:

 controlling the speed of the motor. This requires PWM'ing at the inputs, which is not available.

direction control. To change direction, the indexer must be advanced.

the unused outputs. A smaller package can be used without the added pins

To operate a DC motor, please look at the DRV8828, DRV8829, DRV8870, DRV8871, or DRV8872.