M906 Max Editable Motor Currents (mA) on Duet 2

EducatingSavvas

Hiya - I'm looking to get a confirmation of the max peak motor current for the Duet 2 control board?

I've read that the drivers themselves are capable of 4A, but on the Duet hardware overview that each stepper driver is capable of 2.8A motor current, currently limited in software to 2.4A - is that limited with the M906 command config.g file - and if not is this editable?

I'm currently using Nema 23 Bipolar 1.8deg 1.9Nm (269oz.in) 3A 3.36V Motors for CNC use - thus the need for high torque / amperage.

My steps are set to 1/8 to maintain a higher torque, and M906 motor current set to 2800mA for all active drivers. I'm currently getting some good rapids - at 100mm/s^2 acceleration and 2000mm/min max speed. And a good holding torque with a motor current idle factor of 50%. The holding torque needs to be high enough to allow for manual tool change with spanners. I've also added heat sinks on the drivers and a fan suspended above the entire board - so I'm pretty confident that I can cool the drivers.

Cheers.

wilriker

@educatingsavvas The maximum current is capped at 2.4A so setting any higher value with M905 will still result in 2.4A. You could increase this limit by recompiling the firmware but this will void your warranty as well as increases the chance of frying your board significantly. Also 2.4A is 80% of 3A and 80% is the recommendation to run the steppers at (mainly for longevity because of reduced heat).

Regarding cooling: the Duet 2 is designed to dissipate the majority of the heat to the backside of the board. A fan on the front side is more or less useless.

dc42

@educatingsavvas said in M906 Max Editable Motor Currents (mA) on Duet 2:

I've read that the drivers themselves are capable of 4A, but on the Duet hardware overview that each stepper driver is capable of 2.8A motor current, currently limited in software to 2.4A - is that limited with the M906 command config.g file - and if not is this editable?

If you read section 15 of the datasheet that you linked to, you will understand why we have limited the max current to 2.4A.

EducatingSavvas

@dc42 Thanks guys for the quick reply. So am I correct to understand that the drivers can still boast to 2.8A despite the current limits?

@wilriker I've not heard this 80% rule in relation to CNC use. I'm going to keep the heat sinks on in any case as well - but the thing that's made the biggest difference to over-heating is setting the motor current idle factor of 50%.

I don't think I'll mess about with recompiling the firmware for now - as it seems to be working but is there any literature you recommend reading about how that works. I'm just curious.

Thanks again, Savvas