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A4988 heatsink issue

Posted by Tamjim 
A4988 heatsink issue
June 27, 2017 06:07AM
Hi,

I'm building an XY-plotter. Once I get it working I plan to use it as the X-Y part of a 3D printer where the bed drops as the print proceeds. It may also be used as a laser cutter.

The motor drivers are A4988s with 10mm x 10mm heatsinks. The heatsinks are only attached by paste and move a bit when the board is not level. Also, I've read that blowing air across them is more effective than down on them which could move the heatsinks too.

I'm concerned that the heatsinks will short other components on the board. Can I buy special double-sided tape to secure them?
Re: A4988 heatsink issue
June 27, 2017 07:24AM
Thermal tape will work, but glues are also an option and are easier to find.

Thermal epoxy is designed for this application, but I'd probably use silicone adhesive as it is a decent thermal conductor and is often used for mounting LEDs (and I have a tube of the stuff on hand).

Just be sparse with the stuff so it doesn't bridge any connections. Even if the glue is an insulator sometimes sensitive circuits will be affected as a result of capacitance changes or whatnot.

You will want to carefully clean off the existing paste first. Depending on the current draw of your motors you might not even need heatsinks.
Re: A4988 heatsink issue
June 27, 2017 08:59AM
CA glue will also work when the surface is clean. IIRC the gap between the chip surface and the surrounding SMD parts is near zero, so you have to carefully position the heatsink to avoid shortcuts.
Re: A4988 heatsink issue
June 27, 2017 03:14PM
You would probably be better off removing the heatsinks and using a fan to blow air along both top and bottom of the driver board. Those chips are not designed to have heat removed from the top surface, which is plastic and doesn't conduct heat well. If the board has been properly designed (as much as any board can be that is far smaller than the chip manufacturer recommends for heat removal), it will have thermal vias to carry the heat to the underside of the board.

What current do you need to run the motors at? Perhaps you don't need additional cooling at all - or perhaps you need beefier drivers.

Edited 1 time(s). Last edit at 06/27/2017 03:18PM by dc42.

Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
Re: A4988 heatsink issue
June 28, 2017 04:31AM
Thanks for the replies.

The label on my motors shows "Stepping Motor 17HD40005-22B 20170117 Busheng".
I'm just getting started and have no idea what current is required.
If the heatsinks are needed I will probably cut them down to 7mm x 7mm to avoid shorts.
Re: A4988 heatsink issue
June 29, 2017 12:56AM
Quote
Tamjim
Thanks for the replies.

The label on my motors shows "Stepping Motor 17HD40005-22B 20170117 Busheng".
I'm just getting started and have no idea what current is required.
If the heatsinks are needed I will probably cut them down to 7mm x 7mm to avoid shorts.

I found this data on them:



If it is correct then they are rated at 1.3A, so I suggest you run them at 1.0A or at most 1.1A. At that current, the drivers will need very little cooling.

Edited 1 time(s). Last edit at 06/29/2017 12:56AM by dc42.

Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].

Re: A4988 heatsink issue
June 30, 2017 06:06AM
Thanks. I may eventually get something working, but I will have to stop changing my mind (what's left of it). My initial mechanical design, mostly complete, has a moving motor. I just discovered H-Bot and coreXY. Back to the drawing board...
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