Duet wifi heatsink placement options?



  • Hello,

    Stepper drivers using TMC2100 (SilentStepstick) have 'thermal vias' which allow for effective thermal pathways. Is there a heatsink placement option for the duet wifi or is the only recommendable heatsink placement is on top of the IC chip?

    I'd share a link a video made by Thomas Sanladerer that might help illustrate this but I am unsure if I can share links here.

    Thanks!



  • I was looking at the PCB layout last night… There are thermal vias on these, too.

    10x10mm heatsinks are about the right size to be placed on the underside.


  • administrators

    HowHot: As Guiliano says there are thermal vias under the TMC2660s to spread the heat over the 4 layers of the board. Alot of heat is passed to the thick copper layers on the bottom of the board. Have a look at this blog post for loads of thermal images at various currents:

    http://blog.think3dprint3d.com/2017/04/duetwifi-updated-thermal-testing.html

    You should not need to place a heatsink on the bottom of the board - the copper area is already quite large. What can help if you are pushing 2.4A is to blow a fan over the bottom of the board. This does not need to be a huge high volume fan, just enough to keep a constant flow of room temp air over the bottom of the board.

    P.S. you can certainly share links to videos.


  • administrators

    Update: this older thermal testing post actually shows pictures of the heat spreading on the back of the board:

    http://blog.think3dprint3d.com/2016/07/duetwifi-thermal-testing.html



  • @GiulianoM:

    I was looking at the PCB layout last night… There are thermal vias on these, too.

    10x10mm heatsinks are about the right size to be placed on the underside.

    Thanks for the reply man.

    http://i.imgur.com/WDJyvQM.jpg You can see on the bottom of the image where the labels for the steppers and such are, I assume just above that are the thermal vias, those little pin hole looking spots/pattern. https://youtu.be/mYuZqx8xwTg?t=163 You can see the thermal vias here in this video clearly, shiny copper looking rectangle, the difference that I see is that whatever PCB laminate that is covering the TMC2660s thermal vias isn't covering the TMC2130s thermal vias. Think this is accurate? It's probably likely best to place heatsinks over the 2660s thermal vias, but I wonder why the thermal vias might be left covered.

    @T3P3Tony:

    What can help if you are pushing 2.4A is to blow a fan over the bottom of the board.

    All around more cooling seems better to me than less, even if not entirely necessary, more surface area is good. I am not really sure what 2.4A really means (I know it's current), the datasheet says 2.8A RMS and I guess 4A maybe with proper cooling? I probably don't understand the datasheet very well.

    @T3P3Tony:

    Update: this older thermal testing post actually shows pictures of the heat spreading on the back of the board:

    http://blog.think3dprint3d.com/2016/07/duetwifi-thermal-testing.html

    Thanks. I am guessing that the current limit could be blown away by some decent heatsinks placed over those hotspots, assuming the thermal pathway is good.



  • For what it's worth, I ordered these:

    http://www.ebay.com/itm/321705680592

    They're 10x10x10mm aluminum heatsinks, a pack of 10, for like $3 with shipping.

    Self adhesive, just stick them on the back side on top of the pinhole vias - kind of in the horizontal rectangular section of the upside-down T shape.

    Necessary? Probably not, with a fan.

    But for $3 (and 1 month), I'd say they could be useful.


  • administrators

    Two things to be careful of:

    1. If the heatsinks drop off, they could short out the stepper motor pins. Any damage caused will not be covered by warranty.

    2. Heatsinks may reduce the airflow to drivers further away from the fan.



  • Good points to consider.

    For #1, I like to protect exposed terminal points by covering them with small pieces of kapton tape.

    For #2, the solid base portion of the heatsink appears to be about 3mm tall, with fins making up the rest of the 10mm height.

    Placing the fins so that they're parallel to the direction of airflow will help.

    Are there commands to report on the temperature of the stepper drivers?

    If not, an IR temperature sensor is a easy way to spot check.



  • @GiulianoM:

    ….......................................

    Are there commands to report on the temperature of the stepper drivers?

    If not, an IR temperature sensor is a easy way to spot check.

    I believe DC42 is working on this but the stepper chip will just report when it is close to a limit and when it gets above an absolute limit but not the actual temperature. I stuck a thermistor on the chip with a small dab of epoxy, then use this to control a fan in thermostatic mode that blows air on to the back of the board. You need to create a dummy tool to be able to monitor the temperature. I did a bit of a write up on my blog here https://somei3deas.wordpress.com/2017/04/18/stepper-motor-and-electronics-cooling/

    My stepper drivers never get above 45deg C with 1.8 Amps so I'd say that using additional heat sinks is unnecessary and possible detrimental.



  • Cool.

    I may just start with a fan on active cooling the back with no heatsinks, and control it's speed like how you did…


  • administrators

    @GiulianoM:

    Good points to consider.
    Are there commands to report on the temperature of the stepper drivers?

    The M122 diagnostic report includes the status of each driver, which can include "Over temperature warning" or "Over temperature error".



  • @dc42:

    1. If the heatsinks drop off, they could short out the stepper motor pins. Any damage caused will not be covered by warranty.

    Great advice, thanks

    @dc42:

    2. Heatsinks may reduce the airflow to drivers further away from the fan.

    I'd place heatsinks onto the thermal vias of every driver.

    Are the thermal vias covered by some sort of laminate or fully exposed like on 'SilentStepstick'?

    @deckingman:

    using additional heat sinks is unnecessary and possible detrimental.

    How can heatsinks be detrimental here?


  • administrators

    The thermal vias have mask over the top , we would not want large areas of exposed copper for things to short against.

    I would test without them before adding them.


  • administrators

    The thermal vias are connected to at least 4 different pins on the driver chip, which must remain insulated from each other. If you stick heatsinks on them, you will be relying on the solder mask to insulate the traces from the heatsinks. I advise against that.


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