Active Cooling Stepper Drivers

Abdul Lutfi

Can I run the built in TMC 2660 stepper drivers of the Duet controller boards at 3A beyond their maximum of 2.8A if they are actively water cooled?

ampex_fhm

I'm not sure if the steppers can be configured beyond their rated amperage. I would suggest you invest in external stepper drivers instead. This is probably going to be cheaper than cooking up a watercooling solution for the TMCs, too.

dc42

I don't advise it, because the only thing you could water cool would be the tops of the driver chips, and the plastic tops of chips don't conduct heat well. Try it if you like, but don't ask us to replace any blown driver chips under warranty.

Dougal1957

AFAIK The max current on them is limited in the firmware to 2.4 Amps (You could of course roll your own to overcome this limit)
also bare in mind that it is the underside of the board that provides the cooling path for the steppers and not the Chip Body!

Doug

Abdul Lutfi

@ampex_fhm:

I'm not sure if the steppers can be configured beyond their rated amperage. I would suggest you invest in external stepper drivers instead. This is probably going to be cheaper than cooking up a watercooling solution for the TMCs, too.

I have looked around the forum. It looks so daunting and difficult configuring the firmware and all others…....

I'm actually designing a 3D Printer cum Laser Cutter.

Idex each with dual extruders. Hence 6 Nema17 and 4 Heater (6? in future)
Z-axis is powered by 2 Nema23 rated 2A.
Y-axis is powered by 2 Nema23 rated 3A.

Duet3D is THE only board that can fulfill my hardware requirements. But I'm just troubled by the difficulty that may come with needing External Drivers......

Danal

It is SO EASY to configure to use external drivers, particularly with the various expansion options, I'd definitely go that route to go higher current.

dc42

It's not usual to run stepper motors at their full rated current, because they get very hot if you do. A maximum of 80 to 85% is more usual.

The current firmware limit of 2.4A would be 80% of your 3A motor rating, which may be as high as you want to go anyway. Alternatively, are there any Nema 23 motors with a slightly lower current rating that would meet your requirements? I use 2.8A 56mm long Nema 23 motors for firmware and Duet testing.

Danal

Still, if you wish to over-current the onboard drivers… Keeping in my that I have nothing to do with the Duet3d company, and therefore warranty... a couple of thoughts:

M906 documentation says "Current in Milliamps". The Wiki document does not specify an limits or ranges.
A quick look at the firmware shows that it DOES constrain the values before communicating with the driver chip. There may be several places... one example is in the TMC2660.cpp module, which contains things like:

[[language]]
MaximumMotorCurrent = 2400.0;
constrain<float>(current, 100.0, MaximumMotorCurrent)</float>

Therefore, to even set a current more than 2400 mA (2.4 amps) into the hardware chip, you will need to modify the firmware. It is available on github. Getting set up to build the firmware can be a big deal. The actual change, to raise the constraint, is trivial.

Summarizing: Getting an onboard chip set to a higher current will require changing the firmware. The change is tiny, building the firmware can be hard.

Danal

Next thought is that there is a lot more than the single number "2.8A" when pushing the chip to its thermal limits. The datasheet has several tables showing numbers in the 2.0A to 2.9A range, depending on many factors.

I'd strongly suggest a very close read of the datasheet before pushing a chip to its limits.

Again: I have nothing to do with the company, and it is pretty clear that all of this would void a warranty.

Abdul Lutfi

@dc42:

It's not usual to run stepper motors at their full rated current, because they get very hot if you do. A maximum of 80 to 85% is more usual.

The current firmware limit of 2.4A would be 80% of your 3A motor rating, which may be as high as you want to go anyway. Alternatively, are there any Nema 23 motors with a slightly lower current rating that would meet your requirements? I use 2.8A 56mm long Nema 23 motors for firmware and Duet testing.

I don't know actually…...
Usually a cartesian printer will have the X-axis (Extruders) riding on a Z-axis (Up-down). And the bed running along the Y-axis.

Mine is X-axis (Extruders) riding on a Z-axis (Up-down) running along the Y-axis.
So that means the bed is stationary. The Whole moving Gantry is really heavy considering all parts are machined aluminum and having a 40w laser tube attached.
The Whole Gantry will run along the Y-Axis using ballscrews, powered by 2 Nema 23, one on each side.

I'm looking at 115mm long Nema 23 3A. each.
Is that Overkill?

btw, I really wish I could share with you a rendering of it (uploading a picture)...... how do I do it?

dc42

I can't really comment on your mechanics without knowing more. Those motors may well be overkill. Also, 115mm long Nema 23 motors will have quite a high inductance, so they may need more than 24V driver power depending on how fast you want to run them.

To share a picture, upload it to a public file sharing site and post a link to here between img tags. If using Dropbox, change ?dl=0 at the end of the link to ?raw=1.

dc42

PS - one option is to design your Y axis to accommodate the long 3A motors, but fit the shorter 2.8A motor for now. If you subsequently find that you need more torque, you could then substitute the 3A motors and add two external drivers connected to the CONN_LCD connector plus a higher voltage PSU for them.