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Fried my Ramps / arduino board?

Posted by alexpatrep 
Fried my Ramps / arduino board?
March 17, 2019 07:45AM
Hi all,
I'm building a mpcnc controller kit based on Ramps 1.4 on mega 2560 and DRV8825 driver modules.

Steppers: hanpose 17HS8401-S 48mm Nema17.

According to the datasheet current max is 1.7A -> I was planing to use (1.7/2)*0.9 = 0.765V, but was starting at 0.7V.

I got the marlin firmware flashed, and repetier host connecting to the board. Then (everything disconnected) I connected one stepper motor. I’m able to step the motor, however it made strange noises. And the DRV heat sink got quite hot.
After playing around a bit (changing voltage between 0.3 and 0.8 V - the noise getting more/less loud, but never vanished), suddenly my lab power supply indicated only 7V instead of 12V. Motors do not move anymore.

Now I have th following situation:
I can flash blink example or the firmware. With the firmware, I can connect from repetier host, the voltage to the ramps board is 12V; the DRV output voltage is 0.7V.
As soon as I send the first step to the motor voltage to the board drops to 7V.

I checked the motor (short circuit the to pairs makes rotation harder, i can connect an led to each pair which shines when rotating the axle of the motor. The two inner cables still have a high resistance between them). So I think the motor is ok.
What could I have fried and how?

Thanks
Alex
Re: Fried my Ramps / arduino board?
March 17, 2019 08:02AM
Sounds like a dead DRV8825 to me
Re: Fried my Ramps / arduino board?
March 17, 2019 08:54AM
I tested a different drv on a different axis.
as soon as i send the first step (motor gets engaged) voltage drops.
I tested the motor (resistances and led) and tried different motors (all from the same type/delivery).
Always the same
Re: Fried my Ramps / arduino board?
March 17, 2019 09:02AM
for the 12v to drop to 7v there is either a large load or a failing power supply.
Re: Fried my Ramps / arduino board?
March 17, 2019 09:12AM
my lab power supply is ok. must be between 12v in on the ramps and the motor.
its really strange as the current is lower as the supply supports. so its not that theres not enough coming from the supply
Re: Fried my Ramps / arduino board?
March 17, 2019 09:14AM
perhaps something was not ok right from the beginning. i had 2-3A consumed when the motor was engaded. the heat sink got quite hot.
when i connect the motor directly to 0.7V it consunes only 0.3A
Re: Fried my Ramps / arduino board?
March 17, 2019 09:36AM
you sure you put the stepper modules in correctly?

Same as the purple drivers below


Re: Fried my Ramps / arduino board?
March 17, 2019 11:10AM
yes, potentiometer to the left, 3 jumpers below.
The strange sound was present right after the first stepping command also on stanstill with motor engaged. I thought it should have steady signal on hold. Or is it pulsed also at standstill? A sound could only be due to some frequency on the supply to the motor or not?
Re: Fried my Ramps / arduino board?
March 17, 2019 12:11PM
If the stepper is not on a full step the signal is pulsed to try and balance the stepper between pole positions.

These steppers drivers always make a little noise.
Re: Fried my Ramps / arduino board?
March 17, 2019 05:31PM
Those little plug-in drivers are useless at higher currents like 1.7A. The chip is designed to transmit heat to the PCB, but the PCB area is far too small to get rid of it. Your only chance of getting that setup working at 1.7A is to provide very good fan cooling.

However, stepper motors are rarely run at rated current, because at that current they get very hot. So try a fresh driver but turn the current down to 1A. When you get that working and the cooling sorted out, you may wish to increase the current to 1.2 or 1.3A.

Also, check your formula for current vs. Vref. It depends on the value of the sense resistors used on the driver modules.

Edited 1 time(s). Last edit at 03/17/2019 05:33PM by dc42.



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

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