attaching heat sink to pololu chip - with what?

Hello All

I see many comments re attaching a heatsink to the microchip actually doing the work on the pololu breakout boards to prevent the chip burning out.

I was wondering what one uses for this. I have found various adverts eg. thermal paste on ebay but am not sure this will work as required... will it resist the vibration the machine may produce... is it neccesary to use something else to keep the heatsink in place with this paste just providing thermal conductivity or is the paste a glue as well?

Thanks for any advice.

No you need something like this: [www.aria.co.uk]

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[www.hydraraptor.blogspot.com]

damn that stuff is expensive... and no good for attaching the thermistor either...

Thanks Nop

Edited 1 time(s). Last edit at 11/30/2010 03:04PM by AgeingHippy.

Well actually somebody recommended it to me for sticking thermistors: [hydraraptor.blogspot.com]. I haven't tried it yet.

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[www.hydraraptor.blogspot.com]

Hi AH

I use these for many things including Reprap electronics - and they fit perfectly on GEN3 steppers, they are self adhesive (tape) - http://www.kustompcs.co.uk/acatalog/info_2877.html

9mm ones are also available, they should fit on Pololu.

You could use Aluminium ones, they cost less and do a good enough job -
http://www.kustompcs.co.uk/acatalog/info_2833.html

Rich

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[richrap.blogspot.com]

I just bought some video ram heatsinks... complete with sticker on the bottom... I cut the heatsink into 4... then peel and stick.

Al...

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[araspitfire.blogspot.com]

I have been using this heat sink glue from DX for a while with great results. What it may lack in thermal conductivity it makes up for in strength. I believe you can also get it in smaller tubes from the same site if you don't need quite as much

As always keep in mind the very long shipping times from DX which will only get worse towards xmas.

I use thermal paste (just standard stuff, not arctic silver or anything) on the middle of the heatsink and a drop of superglue on the edges of the heatsink.

I tried 2 types of thermal epoxy, but both were very expensive and messy (2 components that you have to mix at the right ratio) and they never really stuck that well. I've had very good results with the superglue trick.

I stuck mine on with springs and screws, but then I'm putting one video card cooler over 4 pololus. I think ram heatsinks are easiest, most come with thermal adhesive (not to be confused with thermal paste which still requires external mounting of some sort)

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Wooden Mendel
Teacup Firmware

araspitfire Wrote:
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> I just bought some video ram heatsinks... complete
> with sticker on the bottom... I cut the heatsink
> into 4... then peel and stick.
>
> Al...

Hey Al

Have you found the heatsinks alone to be sufficient or do you need to blow air over them as well?

Thanks

I would say it depends on what motors you have - e.g how much current you set for them to get the desired torque.
The point is to run the motors with the lowest current possible, to avoid motors getting too hot. As a result of that, the driver chips wont heat up much either.

I have 12 pololu driver boards but never used any, not even so much as for testing - yet.
Instead, i use the stepper driver board 3.3v with a 3977 and like 3.5-4 cm heatsinks. I have some 1,2A and 1,5A rated motors with like 0.35-0.4Nm torque, i ran them at approx 0.5-0.7A current and that seems to give enough torque so all movements are quite ok, the chips heatsinks are always cold (radiators are at room temp full time while running), and motors are like always "touchable" like 45-50 degrees or so - i guess.

You will need to find the lowest current settings where the motors are happy and give just enough torque, then you will find out what will be needed. To do that, you need to adjust it with the full mechanical setup - to be able to test stepper movements. You will need to start with a very low current setting and go up only if its actually needed. Good luck.

Edited 1 time(s). Last edit at 12/13/2010 04:40AM by NoobMan.

I have three Pololu boards that are jmounted end to end and just cooled with a 25mm fan and a reprapped duct to concentrate the air flow, no heatsinks.

I am not sure what current I am using but I wind it up until either the chips or the motors are just too hot to touch. I want the torque as high as possible to make the motors stiff and minimise backlash and overshoot rather than the minimum.

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[www.hydraraptor.blogspot.com]

Nophead is right, i think his approach is a better perspective.

I avoided setting the max current because with overkill heatsinks and a3977 allowing slightly bigger max currents, the motors were kinda much too hot to my appreciation, so i positioned myself relative to that aspect alone. For myself i just roughly appreciated half current - half torque thingy out of like ~0.4Nm to get half current and ~0.20Nm (as specified "needed"), and further than that i only cared for motors heating up - as i had no issues with anything else. My own impression was that the actual required torque must be a little less than the 0.20 anyway and the motors should run without issues.

I think pololu drivers have their real max current kinda lower, maybe up to ~1A (or maybe 0.5~0.7 rms just a guess, no real clue - but there was a thread on it). Therefore a good setting is probably significantly closer to their top currents, so you end up aiming for max current anyway. And then ofc the chip heat is more of an issue than it is for other boards/chips.

thermally limited currents are calculated assuming an infinite heatsink at 25 celsius. Unless you have one of these (or active cooling ala peltier or phase change) in perfect conditions, you'll never see the rated current. google "chuck mcmanis fet current ratings" for an excellent write-up on calculating power capabilities and heatsinks

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Wooden Mendel
Teacup Firmware

Indeed the drivers currents are hard to get, frankly i am no good at the area. I had read that thread with pololu currents and the posts on that debate but i wouldnt allow to adventure myself on the issue since i'm rather noobish at it.

I think i was probably unsuccessfully trying to point out that while normally, as an "approach" one would set the driver board around the motor and application (e.g. for a 2,5-3,5A chips to use with a 1-1,5A motors ofc max current isnt the objective), on pololu boards the max current is probably so low anyway, that just setting for max current could be the way to go.

As a sidenote, at some point doing some research into why 3.3 stepper driver has ct470pf instead of 680pf (datasheet) or 1000pf (more common over the net in designs i found on a3977), i runned into some datasheet that was supposed to double check the fet values and currents for a3986 (this was somewhat a much debated chip over cnc-zone at that time), and i found it to be fairly nice approach over an 3 sheet xls file for a motor math and its currents - is here [www.c-n-c.cz] I even played with it a little wanting to get something similar for a3977 math -bar fets which are internal- for better documentation on it, but got both stuck on some areas and confused on others, and couldnt find my way out. Keeps bugging me tho, and would love to see something like that still for a3977, as i pretty much got to like this chip so far although its not all that new, but to me it feels somehow solid. Sorry if i jump from one thing to another or if my comments are somewhat messed up, half of my brain is always wandering somewhere else all the time and most of the times i cant even say which side is missing