atmega328p overheating, x axis not working

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revspete
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atmega328p overheating, x axis not working

Post by revspete » Wed May 22, 2019 9:27 am

I have been running the cnc board almost daily now for an automated digital microscope for a few months now without any issues. However, a motor driver (DVR8825) has now blown on the x-axis which is used most often while scanning. I assume the frequent and short steps met with some additional resistance over time has caused it to overheat.

Steps taken:
  • I replaced the motor driver with a new however it did not fix it
  • Y and Z axis both still work normally, however, the heatsinks on the motor drivers appear to be running hotter than I remember.
  • The x axis motor works fine when plugged into Y and Z axis drivers.
  • Step and Dir for Y and Z are working normally however Step and Dir for X appears to be floating between 0.3 - 0.8V.
  • When unplugging all connections to the cnc board and powering it from 5V it draws 150mA and the atmega runs quite warm. I assume something internal has blown.
My new cnc board is on it's way but I want to prevent this from happening again.

Questions:
  1. The DVR8825 has current limiting, over-current and over-temperature protection, short-to-ground and shorted-load protection - so why did it blow?
  2. Is there any protection built into the cnc board for motor drivers failing? I note the 47uF caps for each axis to sink inductive loads, none of them appears blown
  3. Do you recommend external Schottky diodes on motor lines to protect the motor driver and controller? As per https://electronics.stackexchange.com/q ... or-drivers
  4. Does anyone have a recommended motor driver for very short and frequent steps? I have read the DVR8825 are not recommended for this.
  5. If I buy a blank atmega328p and replace the old one, should it be possible to reflash bootloader and firmware? I have equipment for SMD soldering. Is it possible than any other components on the board have been destroyed?
Best,
Peter

Bertus Kruger
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Re: atmega328p overheating, x axis not working

Post by Bertus Kruger » Sun May 26, 2019 7:39 pm

revspete wrote:
Wed May 22, 2019 9:27 am
[*]The DVR8825 has current limiting, over-current and over-temperature protection, short-to-ground and shorted-load protection - so why did it blow?
Had to tell. Do you have heat sinks on them? The tend to run much hotter than A4988

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Re: atmega328p overheating, x axis not working

Post by Bertus Kruger » Sun May 26, 2019 7:41 pm

revspete wrote:
Wed May 22, 2019 9:27 am
[*]Is there any protection built into the cnc board for motor drivers failing? I note the 47uF caps for each axis to sink inductive loads, none of them appears blown
47uf is to protect against power spikes that could kill the stepper driver. 47 is the minimum they recommend but 100uf is better. A power issue could be the cause of your driver blowing. But then the other drivers might have been affected to.

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Re: atmega328p overheating, x axis not working

Post by Bertus Kruger » Sun May 26, 2019 7:44 pm

There are clamping diodes on the TX RX line with the Pi to protect it.

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Re: atmega328p overheating, x axis not working

Post by Bertus Kruger » Sun May 26, 2019 7:49 pm

revspete wrote:
Wed May 22, 2019 9:27 am
[*]If I buy a blank atmega328p and replace the old one, should it be possible to reflash bootloader and firmware? I have equipment for SMD soldering. Is it possible than any other components on the board have been destroyed?
Yes, this could work. Likely the stepper driver could have shorted some of the IO pins on the 328. The question is, is your time worth the effort. You could spend hours trying to fix it if there are unknown components that also failed. (Not that I think there are in this case)

revspete
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Re: atmega328p overheating, x axis not working

Post by revspete » Tue May 28, 2019 7:50 am

Thanks for replies.

I've increased cooling to the drivers adding a fan and airflow to the enclosure they were in.

I'm also changing to the silentstepstick TMC2130 and using their protection boards:
https://shop.watterott.com/SilentStepSt ... or-Drivers

I've order new hats from the NZ shop and a US reseller, hopefully one of the boards will arrive by this Friday.

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Re: atmega328p overheating, x axis not working

Post by Bertus Kruger » Thu May 30, 2019 7:41 pm

revspete wrote:
Tue May 28, 2019 7:50 am
Thanks for replies.

I've increased cooling to the drivers adding a fan and airflow to the enclosure they were in.

I'm also changing to the silentstepstick TMC2130 and using their protection boards:
https://shop.watterott.com/SilentStepSt ... or-Drivers

I've order new hats from the NZ shop and a US reseller, hopefully one of the boards will arrive by this Friday.
Thanks for sharing that.

Very interesting protection board. Where they $6 each or did you get a set of 4?

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