Question on setting the 'run_current' on my TM2209 drivers

[Rusty105]

So like the title says, what do I set these to?

I have a self sourced Switchwire with LDO Steppers
X,Y, & Z are LDO42-STH40-168AC and the extruder has a LDO36-STH20-1004AH6

The spec sheet for the extruder stepper says it is rated for 1.0A Max. Using the "Voron Calculating Driver Current Settings guide", I would get 0.707A or round down to 0.7A for the extruder.

As for the X, Y, & Z steppers, I read that they were rated at 1.68A per phase. Again using the guide I would get 1.19, or rounded down 1.1A

Two questions.....

Is the 'Max' amp of the extruder stepper, and the 'per phase' of the other steppers the same variable, just said differently. (Obviously different values )

And what happens if I run them considerably lower, like 1/2 the value.

Ok, 3rd question, any reason to not just run them at the calculated 0.7A and 1.1A settings?

I am speculating that if I set theses lower then needed I will not get the speeds and accels I want out of this printer?

Thanks
Rusty

 

[claudermilk]

Well, for the extruder you'll get skipped steps and under extrusion (ask me how I know). I expect the same issue with the others, then the homing is lost resulting in shifted layers. I just set my A,B, and Z to the *0.707 value and left them there. It works and no reason I see to mess with it.

 

[Rusty105]

This is why I am asking..... I had my extruder set to 0.3A, or just under 1/2 of the 0.7A recommended spec. I am getting some signs of under extruding, and little skips in the layers . For info I am using a Revo Voron hotend and I am maxing out at 7 mm^3/s with Polymaker PLA. A little disappointing, I though I would get more flow. I thin I am going to set them to .7 and 1.1 and see how it goes....

Rusty

 

[NoGuru]

Like anything it's a balance.
Current to low, like Claudermilk said, will cause missed steps.
Current to high and you are creating extra heat and decreasing motor life.
These things are also dependent on what extruder you use. Torque can be different with different extruders.
What material you use, some melt faster then others.
And speed you print at. If its not melting in the "melt zone" it the nozzle can start to clog and cause skips.

Setting the default current is a good start but if you want to tune the current. Try making a change and running a Max flow rate test and see where you start skipping.