Duet 3 questions

DocTrucker

@deckingman I'd just ran an internet search on Duet 3 and those where the top links. Hopefully airing them will lead the admins to delete or amend. Think one of mine is the shop link.

dc42

I have tested the expansion boards driving 3 stepper motors simultaneously at 4.5A RMS (6.3A peak). I don't have enough high current stepper motors to test all 6 on the main board simultaneously at that current. That's one of the reasons why we've been cautious about specifying the rated current on the main board. The firmware will allow 6.3A peak. We'll do some more tests next week when we expect to have the first version 1.0 main boards.

At high motor currents, the firmware enforces a maximum standstill current percentage. This maximum reduces from 100% at 4.5A or lower peak current setting to 70% at 6.3A peak current setting. The purpose is so that each pair of output mosfets carries at most 4.5A RMS current, whether moving or at standstill, to avoid overheating individual mosfets when the motors are standing still.

nightmare90gt

@dc42 said in Duet 3 questions:

I have tested the expansion boards driving 3 stepper motors simultaneously at 4.5A RMS (6.3A peak). I don't have enough high current stepper motors to test all 6 on the main board simultaneously at that current. That's one of the reasons why we've been cautious about specifying the rated current on the main board. The firmware will allow 6.3A peak. We'll do some more tests next week when we expect to have the first version 1.0 main boards.

At high motor currents, the firmware enforces a maximum standstill current percentage. This maximum reduces from 100% at 4.5A or lower peak current setting to 70% at 6.3A peak current setting. The purpose is so that each pair of output mosfets carries at most 4.5A RMS current, whether moving or at standstill, to avoid overheating individual mosfets when the motors are standing still.

Look forward to seeing the results.

nightmare90gt

If I do the calculations for the nema 34 the max voltage is 45 which I wouldn't want to do for heat purposes. So if I apply 32v to the motors that will put me at 70%. Is there a way to figure the amperage at 32 volts?

dc42

@nightmare90gt said in Duet 3 questions:

If I do the calculations for the nema 34 the max voltage is 45

Do you mean that is the voltage you need at the highest speed you want to run the motors? Or something else?

nightmare90gt

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

If I do the calculations for the nema 34 the max voltage is 45

Do you mean that is the voltage you need at the highest speed you want to run the motors? Or something else?

The max voltage the motor should be driven from my understanding.

dc42

@nightmare90gt said in Duet 3 questions:

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

If I do the calculations for the nema 34 the max voltage is 45

Do you mean that is the voltage you need at the highest speed you want to run the motors? Or something else?

The max voltage the motor should be driven from my understanding.

There are two voltages commonly specified for stepper motors:

The phase voltage is the resistive voltage drop at the rated current. It should be much less than the VIN voltage, but is otherwise irrelevant when using constant current drivers (which Duets and all other modern control electronics use).
The insulation rating. This is usually many tens of volts, and should be higher than the VIN voltage used.

nightmare90gt

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

If I do the calculations for the nema 34 the max voltage is 45

Do you mean that is the voltage you need at the highest speed you want to run the motors? Or something else?

The max voltage the motor should be driven from my understanding.

There are two voltages commonly specified for stepper motors:

The phase voltage is the resistive voltage drop at the rated current. It should be much less than the VIN voltage, but is otherwise irrelevant when using constant current drivers (which Duets and all other modern control electronics use).

The insulation rating. This is usually many tens of volts, and should be higher than the VIN voltage used.

https://www.geckodrive.com/support/step-motor-basics/power-supply-basics.html

This is how I found the max voltage for the motor sounds like the insulation rating your referring to above.

dc42

@nightmare90gt said in Duet 3 questions:

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

If I do the calculations for the nema 34 the max voltage is 45

Do you mean that is the voltage you need at the highest speed you want to run the motors? Or something else?

The max voltage the motor should be driven from my understanding.

There are two voltages commonly specified for stepper motors:

The phase voltage is the resistive voltage drop at the rated current. It should be much less than the VIN voltage, but is otherwise irrelevant when using constant current drivers (which Duets and all other modern control electronics use).

The insulation rating. This is usually many tens of volts, and should be higher than the VIN voltage used.

https://www.geckodrive.com/support/step-motor-basics/power-supply-basics.html

This is how I found the max voltage for the motor sounds like the insulation rating your referring to above.

The formula they give:

32 * √L = VMAX

is specific to the Geckodrive, and does not translate directly to other drivers. What it suggests to me is that the Geckodrive has a minimum quantum of time by which it can adjust the on-time, and that time quantum is quite long.

It's true that very low inductance motors and high supply voltage could be problematic, but to be a problem for the Duet 3 drivers I think the inductance would need to be well under 1mH even with 30V supply.

nightmare90gt

Ah ok makes sense thank you for clearing that up for me.

nightmare90gt

It's true that very low inductance motors and high supply voltage could be problematic, but to be a problem for the Duet 3 drivers I think the inductance would need to be well under 1mH even with 30V supply.

So are you saying that because the motors in question have a inductance of 2mH I wouldn't be able to use the Duet 3?

dc42

@nightmare90gt said in Duet 3 questions:

It's true that very low inductance motors and high supply voltage could be problematic, but to be a problem for the Duet 3 drivers I think the inductance would need to be well under 1mH even with 30V supply.

So are you saying that because the motors in question have a inductance of 2mH I wouldn't be able to use the Duet 3?

Yes, no problem.

nightmare90gt

@dc42 said in Duet 3 questions:

@nightmare90gt said in Duet 3 questions:

It's true that very low inductance motors and high supply voltage could be problematic, but to be a problem for the Duet 3 drivers I think the inductance would need to be well under 1mH even with 30V supply.

So are you saying that because the motors in question have a inductance of 2mH I wouldn't be able to use the Duet 3?

Yes, no problem.

I'm guessing you read it as would and not would not. If so I am looking forward to seeing the progress with this board as I will be using to control my cnc.

dc42

Yes, you can 2mH high current motors with Duet 3.

FWIW the motors I test Duet 3 firmware with are these https://www.omc-stepperonline.com/nema-34-cnc-motore-passo-passo-4-5nm-637oz-in-5-5a-86x86x80mm-key-way-shaft.html?search=34HS31-5504S. But I chose those when the rated current for Duet 3 was lower than it is now.

nightmare90gt

@dc42 said in Duet 3 questions:

Yes, you can 2mH high current motors with Duet 3.

FWIW the motors I test Duet 3 firmware with are these https://www.omc-stepperonline.com/nema-34-cnc-motore-passo-passo-4-5nm-637oz-in-5-5a-86x86x80mm-key-way-shaft.html?search=34HS31-5504S. But I chose those when the rated current for Duet 3 was lower than it is now.

I am looking at this motor for a better pair to the duet board (less amp rating)

https://www.omc-stepperonline.com/nema-34-cnc-alto-torque-motore-passo-passo-13nm-1841oz-in-5a-86x86x150mm.html?search=Nema 34&limit=100

Also maybe you can help me understand the inductance number. Would it be better to have that number bigger or smaller?

Veti

please read the guide
https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors#Section_Inductance