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# Stepper Driver Current Limit & parallel Stepper Motors

New Home Forum Mostly Printed CNC – MPCNC Troubleshooting – MPCNC Stepper Driver Current Limit & parallel Stepper Motors

This topic contains 22 replies, has 6 voices, and was last updated by  danzca6 1 year, 7 months ago.

Viewing 23 posts - 1 through 23 (of 23 total)
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• #5354

Franz Maier
Participant

Do I have to double the current limit of the steppers for setup in the stepper drivers if the steppers are connecten in parallel? Should I stay below the limit in the stepper datasheet?

#5361

Ryan
Keymaster

Yes double, but make sure you are using the amps @12v, not what is in the spec sheet.

For example, [email protected] from a spec sheet. 2A*4V=8Watts 8W/12V=0.667A for 1 stepper, *2 for the X and Y

Start a little below the max rating and move closer to the max if you driver and steppers are cool enough. The drivers I recommend can handle giant steppers if you have a fan on them.

Both drivers use a different equation for voltage at the pot, on the 8825, the voltage should read the same as the 0.667v in the example above.

#5363

Franz Maier
Participant

Thanks!
I was not aware to limit the power and not the current! The datasheet of my Nema 17 says 2A @ 2.8V (5.6W) So I have to limit the current to 0.5A @ 12V for one stepper. This means Vref= 0.5V @ 1.0A (two steppers)

#5364

Ryan
Keymaster

It is pretty sensitive take the decimal further. 0.46v for the z, 0.93v the the others.

So now the cool part is you can over drive the hell out of the the steppers, if you have a fan or 2 on the drivers, so it is kind of an art. I would set them a bit low, .42, .85 and see what temps you get. The steppers can run at up to 100C (usually), although I would never do that. I run them at about 30C or less. I don’t like to push things too far so I ship the boards set at .42 and .7, no fan needed.

#5379

Franz Maier
Participant

Thank you very much for the fast and detailed response and the great work you have done witch the MPCNC!

#5392

Ryan
Keymaster

Thanks for the compliments. I’m super stoked that so many people are building and using them. Hope you finish you build soon and start getting dirty!

#5399

Tomi Hautala
Participant

Just spend hours to try to find what wrong whit the motors, they just whine and do not rotate no matter what i do.
Then noticed jumpers under the step drivers(assembly picture), my ramps dont have any so looked reprap wiki and installed some jumpers and voila motors work:)

#5641

Paul
Participant

I have a question about setting up. I have the same thing with my motors voltage at 2.8 v. However, can I assemble everything with ramps and then check the VREF as stated above or do I need to follow the video under wiring ramps? I am not great with electronics, sorry if its a stupid question:)

#5642

Ryan
Keymaster

My equations and those videos go together. It is different for the a49 drivers though.

If you bought it from here this is already done.

#5645

Paul
Participant

I can do it on the ramps? or do I need a separate control and bread board to set the VREF? I have the same drivers, unfortunately i did not purchase from you, this was something i got for Christmas.

#5671

Ryan
Keymaster

You can do it on the ramps, no problem.

#5721

Paul
Participant

I’m guessing I will have to send from movement commands from software in order to get a VREF ready? Appreciate the help.

#5782

Franz Maier
Participant

Hello Paul,

you have to power the Ramps Board with 12V and measure Vref as discribed in the Video (middle of page: https://www.vicious1.com/assembly/ramps-wiring/)

Then set Vref with the small potentiometers on each Driver.

#5813

Paul
Participant

I am missing something while checking. Measuring from the POT to the ground, I do not get a voltage reading, if I use the pin next to it (DIR) I get a voltage of 4.93 V and when I adjust the pot nothing changes. I currently have the marlin uploaded, everything connected but the motors. I do have the 12 volt power supply going into the ramps.

#5815

Ryan
Keymaster

In the video in the link above it shows how to measure from the pot itself to the negative pin of the power supply. I clamp the multimeter to a small all metal screwdriver and adjust on the fly.

#5817

Franz Maier
Participant

Hello Paul,

you have to measure from the pot to the pin in the Corner opposit (diagonal) to the pot

###### Attachments:
#5821

Paul
Participant

I have done that and I am getting zero voltage. I have also done and the above suggestion to the negative supply. I will invest in a better multimeter and try again after work.

#5841

Paul
Participant

I finally got it to work! Thanks for your help, my new multi-meter must have made the difference because I can now adjust the voltage. I am wiring my extruder head that I bought from you. I can’t find the data sheet to determine the voltage for the driver.

#5842

Ryan
Keymaster

Start at .5v and just check the stepper temps as it prints. You’re a pro now, it will be easy. You want the stepper warm not hot. Not enough power and you will get textured prints from skipped steps.

#5947

Paul
Participant

Everything is hooked up and ready to test my first print once I stabilize my frame, it’s shakey when it stops traversing on the x and y axis but not a hard fix. I love your design, you have amazing skills.

#5950

Ryan
Keymaster

Thank you. It shouldn’t shake, did you glue and screw the corner block and feet down?

#6716

AH
Participant

Hello,

I’m building one of this amazing CNC’s. I’m on a electronic phase (previously I did a Cyclone PCB engraving using a 4988 + Ramps 1.4).
On this CNC I’m using a DRV8825 steep drivers on RAMPs 1.4, as recomended, but I have some questions.
I did a comparation of the pinouts between the A4988 and DRV8825 and i found some differences:
a) On Ramps using A4988, nSLEEP and nRESET signals are just conected together –> on DRV8825 Polulu manual, the same signals must be connected to VDD +5V.
b) On Ramps the VDD is supplied to A4988, this pin it’s a nFault signal on the DRV8825 (output signal). That means we are connecting a output signal to a VDD.
https://www.pololu.com/picture/view/0J3360
https://www.pololu.com/picture/view/0J4124
http://reprap.org/mediawiki/images/f/f6/RAMPS1.4schematic.png

Could you pls confirm if I need to do any rewiring/cutting on Ramps, to use the DRV8825 instead A4988, or it’s just replace one by the other?

AH

#8470

danzca6
Participant

Ryan

Where is the stepper spec sheet? Just got all my electronics in and wanted to get started on it. You were out of stock on the arduino/ramps kit so I had to order from Amazon. So mine isn’t already setup. Of course, you were back in stock a couple days after I ordered. That’s my luck.

And in the RAMPS Wiring page you have a link that is not found. Is that no longer relevant?