Max amperage for motor drivers?

Veti

do not put a heatsink on the drivers. the board is supposed to cool the via ducts.
so run a fan across the backside.

btw what do you mean by maximum? what are you trying to achieve?

also see
https://duet3d.dozuki.com/Wiki/Hardware_Overview#Section_Operating_limits
Stepper drivers Up to 2.4A peak current

3DPotter

@Veti said in Max amperage for motor drivers?:

btw what do you mean by maximum? what are you trying to achieve?

When the print bed moves and I stop it with my hand, I want the motor to then push the whole printer, rather than over torquing the motor.

This is what I meant by heatsink on motor drivers by the way, this is not what they are meant for?

Veti

@3DPotter said in Max amperage for motor drivers?:

This is what I meant by heatsink on motor drivers by the way, this is not what they are meant for?

if your board came with heatsinks its a cloned board where they cheaped out on the pcb copper for the cooling. the board will have problems at high currents.

3DPotter

It didn't come with heatsinks, but we had the idea to use them on it.

Veti

can you post a picture of the back of the board?

Edit. Nevermind. The Based on on the front is an indication that it is a cloned board.

3DPotter

@Veti
Here's the back

Veti

where did you purchase that board? they are be in violation of the license.

whosrdaddy

@3DPotter : those small heatsinks will not help much.
The TMC2660 drivers are not dissipating heat at the top side but a the bottom side.
If you have a genuine board, there is a 2 oz copper layer for the drivers to dissipate their heat into. (clones only have 1oz copper layer and therefore cannot take the 2.4A max load!).
So make sure you cool the backside of the board with cool air. If you want to go higher, I believe the max current has been limited in firmware but not sure... If you need higher currents, better buy a Duet3 board these can go over 6amps.

theruttmeister

@3DPotter said in Max amperage for motor drivers?:

This is what I meant by heatsink on motor drivers by the way, this is not what they are meant for?

The Trinamic chips are designed to use the PCB as a heatsink. There is a large pad under the chip that is soldered to the board and conducts away the majority of the heat. In good PCB design for this use, you have multiple vias that then carry the heat through the board so the underside will act as a heatsink. If that has been done correctly, you can then attach metal heatsinks to the underside of the board under the drivers and further improve the cooling.

If you want to be really clever, make a nice milled aluminum case for your board, with raised areas that will let the whole case act as your heatsink.

Heatsinks on top still work, just not as well.

engikeneer

@3DPotter FYI maybe a clone as it doesn't have the CE mark on the front and doesn't have the Duet QC sticker on the processor... this is only really relevant in that some clones skimp on the copper layers in the PCB so the board won't handle higher currents so well.

Back to your question. Adding heatsinks to the top of the drivers is not recommended on the Duet boards. The drivers have thermal feet (can't remember the technical word..) on the back of them which conduct heat very well to the board. The board is then designed to conduct this heat out over its surface. Large surface area, means great convection cooling. If you're pushing the currents high, best bet is to get a lot of cooling on the board from a fan or two blowing cold air over the top/bottom surfaces of the drivers

The top of the driver chips are plastic, so won't conduct heat to your heatsinks very well. In addition, they may impact the air flow from your cooling fans to the board so could actually make things worse... typically you put heatsinks on small chips (e.g. stepsticks) to increase their surface area, but they should usually go onto the PCB too, not the driver

FWIW, I run my duet at ~1.6A and have a 30mm axial fan blowing over it and they stay barely warm. Thats not really at the limits you're talking though! I do know that they will report over temperature warnings if they detect they are getting too hot, and shut down if they actually overheat. Might be worth sticking some big fans over the board and just seeing what happens?

If you really need more grunt, it may be time to look at the Duet 3, or even some TMC5160 stepsticks as external drivers (with heatsinks and cooling fans!)

engikeneer

@whosrdaddy @theruttmeister dang you beat me to it...

theruttmeister

@engikeneer said in Max amperage for motor drivers?:

@whosrdaddy @theruttmeister dang you beat me to it...

lol.

Fun fact!

You can actually exceed the rating on most Trinamic drivers by quite a lot, if your heatsinking is good enough.
Plus the Trinamic guys are all very nice friendly engineers. I think the 3D printing world took them by surprise a bit, but they were horrified when they saw everyone was using Allegro chips back in the bad old days.

Phaedrux

If you really need to provide more current for larger motors the Duet 3 would be the way to go. Or external drivers if you want to go that route.

zapta

@3DPotter said in Max amperage for motor drivers?:

I want the motor to then push the whole printer, rather than over torquing the motor.

I wonder what is the motivation for this requirement. Can you explain?

As for the driver getting too hot. Don't they protect themselves and report to the firmware?

lord binky

Its pretty simple to drum up a duet mount with holes for a couple fans to blow over the backside of the board (which is your heatsink by design) as well as lots of designs out there that would be easy to modify. I have a couple near silent fans ( I forget if they were 40 or 60 mm fans) blowing on the back of the board and my temps ( drivers and CPU) stay nice running the drivers at 2.4A. I know I haven't seen the processor go over 26C and have never gotten a driver temperature flag in the diagnostics.

Phaedrux

@zapta said in Max amperage for motor drivers?:

I wonder what is the motivation for this requirement. Can you explain?

I'm guessing he just wants a lot of power considering the weight of the clay building up on the spinning table.