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DRV8825 Current Limit Not Working

Hi,

I have a DRV8825 board. The phase resistance of the motor I am trying to run is 3.6 ohms. Here is my pin connections:
VMOT -> 12V power supplu
Step -> IO Pin on my microcontroller(3.2V)
Dir -> IO Pin on my microcontroller(3.2V)
/SLEEP, /RESSET -> 5.2V pin on microcontroller

Ground Pins are grounded, and phase pins connected to the motor.

Without any current limiting with 12V supply and a phase resistance of 3.6 ohms it would draw way to much current for for the driver and motors.

Therefor I want to limit the current to about 1A so I need to adjust the POT until the reference voltage is about 0.5V right?

As soon as I switch on the power supply the voltages of the phase pins goes very low. Like 0.6V.

Why would this be? Am I using it in correctly?

It is possible that your 12V power supply is overloaded and shutting down. Check the voltage at the power supply terminals while it is connected to the driver.

Tell us about the V/A characteristics of that power supply, or post a link to the product page.

Hi Jim,

The power supply can give up to 2A at 12V. I did some measurements and we actually measured 1.9A coming out the power supply by connecting the power supply directly onto the motor coil at 7.5V.

Also the VMOT pin measures fine(12V).

The weird thing is that I got it working by adjusting the VREF of the POT to about 320mV. Then I was able to step the motor. With the POT at that position I measured about 0.5A coming out the power supply and about 0.6A per phase of the motor(The voltage on each phase was less than 12V).

I have six of these drivers. I have only tested 2 and they both do the same. Its not a knockoff brand.

What could be going on here? Can the drivers really handle 2A?

Regards,
Gerhard

As everything is turned on(Initially VREF is at 320mV) I gradually increase the VREF voltage. And at about 400mV the driver stops working. It just cuts out, outputs a low on /FAULT, and the motor has no more holding torque.

If I understand this correctly, the power supply can’t actually deliver 2A at 12V, and the output voltage drops to 7.5V. Since the DRV8825 requires 8.2V minimum for the motor power supply, it won’t function correctly either.

If so, you need a beefier power supply. Also, according to the Pololu docs, you can’t expect the DRV8825 to support more than 1.5A/winding without extra cooling, but I suggest to plan for at most 1 A/winding.

Hi Jim,

So the power supply can probably do 2A @ 12V. I could not test this but that’s the rating of the power supply.

To test if i could get 2A out of the power supply i switched the voltage to 7.5V and connected it to the motor coil with has a resistance of 3.5 ohms and then measured the amps. Didn’t have another way of getting 2A out the power supply.

When connecting up to the driver i switch the power supply to 12V. If the power supply can give 2A @ 7.5 then it should easily be able to give at least 1A @ 12V? But the highest amps we measured out the power supply while being connected up to the driver was about 0.5A before the driver stopped working.

I will try a 3rd driver and a bigger power supply.

It may be that the problem is not the power supply, but since you haven’t posted links to the motor or the power supply we can’t check.

Please do that, and post a photo of your setup. Have you CAREFULLY soldered the connections to the motor driver, especially the motor wires? Don’t use a breadboard for high currents, as the tracks will burn. Intermittent motor connections can instantly destroy a motor driver.

It is never a good idea to use equipment at its maximum rating. Engineers and manufacturers often derate by a factor of 2 or more for safety. If you anticipate a 2A current draw, use a power supply rated at 4A.

That said, the average current draw of a properly configured stepper motor and driver drops as the power supply voltage increases. A 24V, 2A power supply should be fine and the motor response will be snappier.

Hi Jim,

So i tried a bigger power supply and that seemed to do the trick. Not sure why as I was getting issues on 0.4V for VREF on the old power supply that suppose to be a 2A one. Maybe I messed up my measurements.

Anyway its working and thanks so much for the help and advice. You guys have great support and my next drivers will definitely be from you again.

Regards,
Gerhard

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