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DRV8847: DRV8847PWR: Unsure why it wont run nema

JO Ee Liew
Prodigy 10 points
Part Number: DRV8847

I am trying out the drv8847pwr as my prototype as nema 17 stepper motor driver. I have tried 2 stepper motor on the breadboard with similar configuration and only swapping out stepper motors. Below is my setup:
Stepper motor A: www.ebay.com.au/.../173343080042
Stepper motor B(48steps): www.digikey.com.au/.../417812

My setup is "4 capacitors 470uf" and a 10uf capacitor setup near to the VM, Both isense is gnd, the mode is not connected. Sleep pin is logical 3.3v high. Trq are not connected. Both ISENs is tie to ground for now.
Don't think heat is a problem, but I have placed the heatsink on top of the drv8847.
I have I have no issues running clockwise fullstep the `stepper motor B` where the VM is 5V.

However, `Stepper motor A` with higher current 0.7A per phase is not moving at all at VM at 3.0V. Any idea what went wrong with my setup?

  • 0
    Genius 3580 points

    Hi JO,

    Breadboard + adapter are not good solutions for most modern motor driver ICs including DRV8847. Please, post some picture or website with an adapter that you use, it may be possible to make it work to some extend.

    What motor speeds do you need for your application? At the moment you try to run motors at their nominal voltages 5V and 3V in voltage mode (no current regulation), it may be sufficient to run these motors only at very low speeds. To run motors faster you will need higher voltage, lets say 12V and current mode ie. sense resistors. Please, do not try it before reviewing your adapter, but even after making any possible improvements to that adapter there will be still high risk of damaging IC.

    Heat will be your main problem if try to use DRV8847 at 0.7A, you will need well designed 2-layer or even 4-layer board to dissipate around 2W of heat. Trying to use DRV8847 with an adapter + breadboard you will get additionally problems with parasitic inductances which can cause voltage ringing and damage the IC.

    If you need 0.7A, a safer and easier option would be driver with a bit lower Rdson (less heat) and starting with EVM board for that driver and then design you own PCB. If you want to run motor faster driver with higher voltage (24V or 36V) would be necessary. The very good think is those 4 caps of 470uF at VM, they can absorb some braking energy if motor is slowed down from high speed or during resonances and save IC from overvoltage. The heatsink that you use will be a great help to dissipate heat.

    I would suggest to read https://www.ti.com/lit/an/slva959a/slva959a.pdf. Using oscilloscope current probe with an oscilloscope will allow you to better understand what is going with motor and driver. Cheap probe like https://www.amazon.com/Hantek%C2%AE-Current-Clamp-kHz-20mA/dp/B06W2KFZLW would be enough for your needs.

    Regards,

    Grzegorz

  • 0 in reply to Grzegorz Pelikan
    TI__Mastermind 37683 points

    Hi Grzegorz,

    Thank you for your comments.

    Hi JO,

    As Grzegorz stated, heat will be a major problem specially at 0.7A current. I recommend getting a DRV8847EVM to evaluate the motors.

  • +1
    Prodigy 10 points

    Heat was not a problem at all, not sure because my weather is in the winter climate. 

    It was the breadboard afterall.

  • 0 in reply to JO Ee Liew
    Prodigy 10 points

    Just in case anyone is wandering which defective breadboard. 

    I got the breadboard when I bought this Microsoft IoT Pack for Raspberry Pi 3 - No Pi Australia (core-electronics.com.au) many years ago and there is the link to the breadboard is shown Full sized breadboard Australia (core-electronics.com.au). Coreelectronics has been in my recent purchase was good but just dont get the breadboard. 

    And I rewire everything on this breadboard https://www.digikey.com.au/product-detail/en/adafruit-industries-llc/239/1528-2143-ND/7244929 and using only 2 470uf caps instead of 4 and IT JUST WORKS last night. 

    Going to try a few more nights to see if there is any consistency. 

  • 0 in reply to JO Ee Liew
    TI__Mastermind 37683 points

    Hi JO,

    I'm glad you were able to fix the issue and thank you for sharing it. I will close this thread for now but feel free to reply back if you require further assistance.