Mystery controller resetting

Hi all, I'm tearing my hair our trying to figure out why my printer stops during prints. I have a home built H-bot running Marlin on a cheapo MKS base 1.3 controller with a gLCD. It's been working fine but the controller recently started randomly resetting during a print and I don't know why. I've watched it happen, the glcd goes blank and restarts as if you've hit the reset button, hotend/bed are set back to 0.

I originally chalked it up to crappy cheap electronics but I've since swapped the board out for a Rambo and had the same issue. Ditto the gLCD/SD reader. I've got the heat bed current limited by PWM as the resistance is too low (mk3 alu - supposedly), could this cycling be causing interference or power supply issues?

Any insights would be welcome.

Rob.

What is the resistance of the heated bed, and what power supply are you using?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I can't remember exactly, but it was too high on the 24V circuit (6 or 7 ohms maybe?) and was only drawing 4 amps. It's one of those chinese copies that was supposed to be a mk3 but is really a MK2 on aluminium. Anyhow I'm running 24V on the 12V terminals with PWM limited to 150 to keep the current to about 8 amps so as not to burn the controller. PSU is 400W 24V.

The resistance across the 12V terminals of a PCB heater is typically 1.2 ohms. On a 24V supply, that would draw 20A, which will overload the PSU during the on-period. As you say you get 8A average with PWM=150, the resistance is probably higher, nevertheless you are probably still overloading the PSU. The output capacitors on the PSU are unlikely to be large enough to smooth out the current draw sufficiently at the relatively low PWM frequency. So the PSU may be cutting out due to overload. Then, with the heated bed effectively removed from the circuit, it starts up again.

Your PSU probably has a voltage adjustment potentiometer at one end of the terminal block. Have you tried turning it all the way down, to reduce the output voltage by a few volts?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'm not familiar with the MKS 1.3 board, does it have separate terminals for 12V and 24V for the heated bed? I'd get a 12V PSU and run the electronics on that, and use the 24V PSU exclusively for the heated bed.

I'm also running my 12V heated bed on a 24V PSU, but it's a dedicated PSU just for the heated bed, the rest is powered by a 5A 12V PSU. I will soon replace it with a 20A 12V PSU, I'm planning to add a second extruder to the setup (Prusa i3, ramps 1.4)

It could be that the 5V regulator is overheating at 24V input voltage. It's usually recommended to have a PSU between 4 and 8V higher than the regulator, so 5+4 to 5+8. 12V is within the recommended range. 24V on the other hand is too high. You'll need more cooling or change the regulator to a heavy duty version.

Edited 1 time(s). Last edit at 09/02/2015 02:33PM by imqqmi.