Where to put a bigger heatsink for the A4988

Hi,

I want to install a bigger heat sink for the A4988 instead of the 9x9mm standard ones.

My problem is that despite all precautions I'd managed to burn two so far. I don't think it was a short circuit neither did I disconnected the driver while power was on. The motors stopped suddenly and the small heat sinks were very hot, so I think the power dissipation for my 24V steppers isn't enough.

I was wondering if I can connect a bigger heat sink directly to GND like in other drivers such as the L298N or maybe to another pin. Really need someway to cool down the drivers.

(Some extra information: I'm already using a 12V fan directly above the drivers. Where I live it is damn hot.)

Thank you in advance.

The best heatsink for plug in A4988 drivers that are mounted on top of the PCB is a 4-layer PCB instead of the 2-layer one that is usually used, a fan blowing air over the PCB, and no heatsink at all on top of the chip. The chip is designed for the heat to be carried away via the thermal pad on the bottom of the chip and then the PCB. The plastic top of the chip is too much of a thermal insulator to conduct heat away from the chip well, and putting a heatsink there reduces the amount of air reaching the PCB.

I have seen DRV8825 driver modules with the chip mounted on the underside of the board, thermal vias on the board to carry the heat to the other side, and a heatsink mounted on the other side which is the top of the module. This is a sensible arrangement. But I haven't seen any A4988 or A4982 modules like that.

Plug-in driver modules have far too little PCB area to cool the chip effectively. That's one of the reasons why the drivers on boards that have built-in drivers are much more reliable than plug-in drivers, and why they can be run closer to their rated current.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The only way to get better cooling on the pololu style drivers, is to use some wire wrap or arduino headers to raise them up so you can put the heatsink underneath on the pc board and have a fan cool them from the side.

Quote
stephenrc
The only way to get better cooling on the pololu style drivers, is to use some wire wrap or arduino headers to raise them up so you can put the heatsink underneath on the pc board and have a fan cool them from the side.

I've made such a raised driver and also placed the stepper-output pins directly on top of the pcb instead of routing it through RAMPS.
That allows better air flow through the pins.

IMHO the best way to use the a4988 drivers is to NOT push their limits. Better use smaller steppers and print slower than taking the risk of an overtemp failure.

Active cooling system
Aluminum plate (heat pipe better) under driver boards,
boards thermal pasted to plate

Peltier cooler on plate (cool side pasted to plate)

May have to run board in dry nitrogen to prevent frosting

Can run drivers at very high current with active cooler?

There is not much room under the drivers because of the jumpers and capacitors.
I would think a thin aluminum strip would fit between, but could cause shortcuts...

Some of the a4988 drivers are current limited by the potmeters and shunt resistor values. Even with liquid nitrogen cooling you wouldn't be able to crank up the current without modding the drivers.

Edited 2 time(s). Last edit at 10/20/2016 03:39PM by o_lampe.

For what it's worth:
For me, I have been using my RAMPS 1.4 board for about 1 1 /2 yeas now and some times I drive it for long prints (the 8 or 9 hour type).
I use NEMA 17 motors, with a holding power of 84 oz. and 1.5A per phase maximum. The current is calculated to use only 1 amp per phase.
I'm using A4988 drivers with the standard 9 x 9 mm cooling fins. In addition I have a 50mm fan(s) mounted directly above the drivers which runs all the time.
The fan(s) turns on the same time the board is booted up. The board is mounted inside a box that I made which also has some other hardware in it.
There are a total of 4 fans mounted on the box, so that there is all kinds of air movement. 2 fans in, 2 fans out. So far no problems (knock on wood).
Some might say this is over-kill -- I say perhaps.

When I was building the printer.


If you have a functioning printer then you could create an air duct to channel the airflow over the driver chips of the controller board.
If you wanted to get fancy you could make the duct surround the board so that both the top and bottom of the board gets air flow.
If you do this you might want to consider using 2 fans, one to push and one to pull the air across the board (forced air flow).
That way noting would have the chance of being shorted out.

In my case notice the fan on the back wall of the (left picture), it is used to exhaust the air. What you don't see is that there is a fan in
the top of the box which blows air down on to the driver's.

Give it some thought, I'm sure that you can come up with something that can be printed to direct the flow of air so that other options will
not be necessary. Combine that with safe practices on current control thru the drivers and you will be "golden".
Besides it kind of nice to say "look what I created". Most of all Have Fun.

Edited 1 time(s). Last edit at 12/14/2016 01:45PM by kd6hq.

Quote
o_lampe
There is not much room under the drivers because of the jumpers and capacitors.
I would think a thin aluminum strip would fit between, but could cause shortcuts...

Get wire wrap headers or arduino headers and use them as "spacers" to get the needed room underneath the drivers to fit a heatsink.