Heat Conductive Materials

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4Springs
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Heat Conductive Materials

Post by 4Springs » Wed, 30 May 2018, 16:12

Does anyone know of a heat-conductive material suitable for ensuring heat transfer between my motor and cooling coils?
The motor is 270mm in diameter, and is surrounded by copper tubing which coils around it. The motor is not smooth, and the coils are not even, so there is probably little actual contact between them. The tubing covers an area 150mm wide:
IMG_1660.JPG
IMG_1660.JPG (186.78 KiB) Viewed 263 times

Something like this silicone pad might be good:
Silicone Pad.png
Silicone Pad.png (153.08 KiB) Viewed 263 times
But it is small. The circumference of the motor is about 850mm, so I'd need 850 x 150mm wide - or about 15 of those pads. Then ideally I'd also like to fill the space between the coils and the heatsink (currently just a piece of galvanised sheet) above them, so the same amount again makes 30 of them.

Any suggestions?

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jonescg
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Re: Heat Conductive Materials

Post by jonescg » Wed, 30 May 2018, 20:11

I spend most of my days researching exactly what you seek :)

What you can do is pick up 1 kg of thermally conductive epoxy resin. It's got a thermal conductivity of 1.0 W/m.K which is high for a plastic (typically 0.1 W/m.K), but woefully low compared to metals (aluminium is 204 W/m.K and copper is 380 W/m.K).

I bought some from a Chinese seller called U-Sheen. It's pretty good and reasonable as an adhesive too. I have about 2 kg of the stuff but I need that for the Prelude battery - however whatever is left should be enough to fill the blanks.

http://www.usheenthermal.com/thermal-gel/
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Richo
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Re: Heat Conductive Materials

Post by Richo » Thu, 31 May 2018, 12:34

There is also goop in a tube which might be more practical to apply.
AS1803-310ML
Farnzy has some about $40/tube 8497400.

Didn't look much so there maybe something better than this.
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4Springs
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Re: Heat Conductive Materials

Post by 4Springs » Fri, 01 Jun 2018, 15:34

Richo wrote:
Thu, 31 May 2018, 12:34
There is also goop in a tube which might be more practical to apply.
AS1803-310ML
Farnzy has some about $40/tube 8497400.
For those following along at home, the last line of Richo's post means that the online-retailer called Element 14 sells this product. He's nicknamed it Farnzy, presumably because it used to be called Farnell, and he is old.
This is why I asked on this forum of course, I spent hours looking through stuff on the Element 14 website without finding that particular product...

The goop has a 'tack free' cure time of 4 minutes. Sounds like it sets hard.
The description that jonescg gives of 'epoxy resin' sounds like it would set hard - although the product linked is described as a silicone gel, which sounds softer. What's your experience tell you Chris?
The reason I am thinking about this is that I'm going to need to apply this stuff in situ. I can loosen the coils but not remove them, as they are plumbed up to the heatpump compressor now (unlike in the photo). Something too runny will run down the motor and drip out the bottom. Something that sets too quickly will be dry and hard before I can tighten up the coils again. I put heatsink paste on it originally, so it will be greasy, and probably dirty because dust will have adhered to it.
I'm a bit hesitant to use something that sets in such a way that it makes removing the coils difficult in the future.

Chris' mention of the conductivity of metal has got me thinking though - could I use folded sheets of aluminium foil? Perhaps sandwitch a little heatsink paste between multiple sheets? Would the aluminium and copper react with each other? The surface of the motor is painted.

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Richo
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Re: Heat Conductive Materials

Post by Richo » Tue, 05 Jun 2018, 12:45

4Springs wrote:
Fri, 01 Jun 2018, 15:34
He's nicknamed it Farnzy, presumably because it used to be called Farnell, and he is old.
Damn Right I'm old :lol:
4Springs wrote:
Fri, 01 Jun 2018, 15:34
The goop has a 'tack free' cure time of 4 minutes. Sounds like it sets hard.
Yeah it does set harder than your regular silicone.
I'd go with 10 day old dried out cake.
4Springs wrote:
Fri, 01 Jun 2018, 15:34
I'm a bit hesitant to use something that sets in such a way that it makes removing the coils difficult in the future.
The goop will break apart if pulled - like old dried out cake.
You could put a layer of Kapton tape around the motor where the coils sit.
This would make it easier to pull off later.
But it looks like it could be difficult to get the Kapton tape on.

I'd go with goop over epoxy.
And I don't like the idea of sandwiches.
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Re: Heat Conductive Materials

Post by jonescg » Tue, 05 Jun 2018, 13:14

Aluminium and copper will corrode quite quickly, so a pourable compound would be ideal. The stuff I have will pour slowly, but you can also fill a 50 ml syringe and force it into nooks and crannies. It takes about an hour to set firm. If you ever needed to remove it you can probably chip it off. They have a selection of products, including encapsulants and gloops, but if yuo can be sure it won't leak out the bottom or the sides, loosen it off, fill 'er up, and tighten the clamp again.
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Re: Heat Conductive Materials

Post by 4Springs » Fri, 08 Jun 2018, 18:45

jonescg wrote:
Tue, 05 Jun 2018, 13:14
if yuo can be sure it won't leak out the bottom or the sides, loosen it off, fill 'er up, and tighten the clamp again.
No, definitely can't seal the bottom or sides. Even if I could, I doubt that it would fill the spaces well, there would be air bubbles everywhere.
I'm going to have to take the sheet-metal straps/clamps off, spread stuff on/in/through the coils with a spatula, then put the straps back on and tighten them up. The coils will uncoil somewhat once the tension is released, and will move again when tightened. Richo's goop would be ok to apply I think, but would set too quickly. The coils would be set into their uncoiled positions and I wouldn't be able to tighten them up again.
I've had a better look through Element 14's offerings now, and found this polyurethane resin: http://au.element14.com/electrolube/ur5 ... conductive
It gives the viscosity as 30,000 MPa s at 23 degrees C, which according to google is a bit thicker than honey. "Usable life" is 15 mins, "Gel time" is 40 mins. I think these properties would give me time to get it spread into the right places - I reckon it will be thicker and cure slower at the temperatures I'll be working at. It will end up in my face though, since I'll be working from underneath the car.
I guess that 250g would be enough. Perhaps I should do one coil at a time in case it is not.
It's even coloured black! Only trouble is that it is out of stock, with stock not due in for another month. Might give me time to think of what I can use instead of the galvanised iron sheeting to hold the coils in place. I'd love something I could attach fans to.

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Re: Heat Conductive Materials

Post by jonescg » Fri, 08 Jun 2018, 19:59

4Springs wrote:
Fri, 08 Jun 2018, 18:45
It will end up in my face though, since I'll be working from underneath the car.
Funny thing about gravity... :lol:

From your picture there I wonder if you couldn't secure the copper coil ends somehow, loosen the clamps and pack Plasticine all around the sides were it might leak out. Then sort of fill er up. Clamp it all back on and hope you never have to remove the motor again.
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