The description page:
states that heat sinking is required if driving >1 A. Allegro’s datasheet shows that the A4988 has a big thermal pad on the bottom and that the board “should” have bit thermal vias to conduct heat to the bottom of the board. Does the Pololu board have these? If so, is there a recommended way to add a heat sink to the bottom of the board?
The description page:
Our A4988 carrier does have a thermal pad and vias under the chip, but we do not have any suggestions for adding a heat sink and generally view adding a heat sink as an advanced modification that should only be made by those who have experience with that kind of thing. By the way, heat sinking is just one way to cool the device (e.g. forced air flow might be enough if you are near the 1A limit). Also, if you need more than 1A per phase, you might consider the black edition of the A4988 carrier, which can handle around 1.2A per phase without additional cooling. You could also look into our DRV8825 Stepper Motor Driver Carrier, High Current, which is similar to the A4988 carriers in many ways, but can handle around 1.5A without additional cooling and offers 1/32-step microstepping.
Thanks, Brandon. I intend to use the drivers in a laser cutter and I doubt the average load over any period > 2 seconds will exceed 1 Amp, so I probably do not need anything at all. However, a laser cutter already needs water cooling, so the incremental cost of extending the water cooling system is very small: it’s just a “small matter” of running a copper tube and figuring our how to bond the tube to the heat source. The choices are to bond to the top of the device and hope it works, or bond to the ground plane portion of the bottom of the board and hope it works. My stack-up is BBB under CRAMPS under the driver cards. I bought this as a fully integrated and tested solution, so I didn’t have the option of inverting the stack to expose the bottoms of the boards. I can add additional long pins to raise the drivers enough to put copper tubes under them.
My plan is to go with no heat sinks and measure the temperatures. If they get too high, then worry about adding heat sinks.
Extending the watercooling is just asking for trouble unless you want to just do it for the challenge of it and to improve brazing etc. Also you are not likely to really improve things by watercooling because you have the thermal junction all the way from the die to the watercooling that will take up a bunch of space and slow down heat transfer, limiting how much the watercooling can help.
There is a lot of info about heatsinking A4988 pololu drivers if you google “reprap a4988 heatsink” or something like that.
In the past i’ve used tiny copper blocks on the a4988 drivers when I wanted to eek slightly better current, but it’s marginal and it’s easy to short the pins. Best to use a fan especially if you have a couple drivers. Right now I have a nice little 120mm slow fan running over my 4 3D printer a4988 drivers and it greatly improves the chip performances. Remember conductivity by forced air can often 10x better than passive.
I recently tried silicone thermal adhesive and it’s much easier to use than thermal epoxy by the way, for bonding heatsinks. Thermal tape exists too but can break. Basic crazy glue is at the thermal limts of the glue when used on these chips (I cant recommend it.)
As a reminder stepper drivers don’t really have an “average load won’t exceed 1A” unless you’re shutting the driver on and off frequently (and you won’t be with a lasercutter). Average load will be whatever you set the limit to, in contrast to DC motors where they will have peaks and reduced running currents.