Duet 3 expansion board stepper driver thermal tests

evan38109

I admit that the Duet3 is getting pretty exciting to me. I've been modding my Prusa MK3s and starting to hit the limits of what I can do with the EINSY. This guy, though...

A Former User

@evan38109. I've been modding my Prusa MK3s and starting to hit the limits of what I can do with the EINSY. This guy, though...

How very dare you... don't you know that prusa printers are perfect and everything he produces is better than anything out and his own original idea.. well at least in his own mind anyway...

zapta

@t3p3tony said in Duet 3 expansion board stepper driver thermal tests:

dissipating max of ~0.34W per FET in a dual package = 0.7W

@t3p3tony, I am curious, when you computed 0.34W, did you need to factor in the chopper transition periods where the FETs have high resistance and significant current?

Also, I am counting 3 TMC's and 12 dual package FETs which results in 8 FETs per TMC instead of the expected 4. How come?

evan38109

@calvinx said in Duet 3 expansion board stepper driver thermal tests:

How very dare you... don't you know that prusa printers are perfect and everything he produces is better than anything out and his own original idea.. well at least in his own mind anyway...

Heh, the Prusa is a great little machine, and if I just wanted to print, I'd leave it as is. Great for modding, too -- I got it printing 0.02mm layers and looking good.

I'd like WiFi, though, and more current to drive some different steppers without hitting thermal issues. (Though 6.3A is overkill, I'd be happy with a solid 2A.) Unfortunately, Duet 2 WiFi uses TMC2660 drivers, which don't support Trinamic's StealthChop, and I'm not willing to give that up. StealthChop is significantly quieter, prints smoother, and is easier to tune. The Maestro uses TMC2224's, which don't support StallGuard, so no sensorless homing. Well, no WiFi on the Maestro, either. If you can't tell, I've been keeping an eye out for a replacement that checks all the boxes.

Anyhow, apologies for drifting off topic. Looking good, dc42!

dc42

I think you are mistaken in thinking that stealthChop prints smoother. Also, printing in stealthChop mode makes it much more likely that you will get a skipped step if the nozzle hits a blob or obstruction. StealthChop doesn't work at all at high speeds, which is why the drivers switch over to spreadCycle at higher speeds. But stealthChop is effective at reducing noise at standstill and low speeds.

The TMC2660 drivers support coolStep which is the forerunner of stealthChop. It is configurable via M915.

dc42

@zapta said in Duet 3 expansion board stepper driver thermal tests:

Also, I am counting 3 TMC's and 12 dual package FETs which results in 8 FETs per TMC instead of the expected 4. How come?

Each H-bridge needs 4 mosfets. You need one bridge per motor phase.

zapta

@dc42 said in Duet 3 expansion board stepper driver thermal tests:

You need one bridge per motor phase.

Bingo.

@dc42, one more question if you don't mind, do the mosfets get hotter with 12V than 24V since the current consumption from 12V source is higher for same stepper power?

T3P3Tony

@zapta not specifically because the stepper drivers are chopping to limit the current through the Motor could (and hence the FETS and sense resistors)

zapta

@t3p3tony, yes, you are right. I asked around the the mosfet's power depends on the coil current, not the supply current (which is roughly double for 12V compared to 24V).

I also run an experiment with a Pololu stepper driver and the temperature is about the same for 12V and 24V.

JRDM

@evan38109 said in Duet 3 expansion board stepper driver thermal tests:

I admit that the Duet3 is getting pretty exciting to me. I've been modding my Prusa MK3s and starting to hit the limits of what I can do with the EINSY. This guy, though...

Do you have any particular reason to put Duet 3 on that though?

I feel like Duet Maestro is a better fit for the most part.

The regular Duet2 is more capable than most desktop users need. The biggest thing I want is direct support for 4 wire fans. Even though my bigger machine can use a little more motor current, it works pretty well at 2.4A.