SSR-90 Mag Heatsink design problem

zelda

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I'm builing my last maglite, but for some reasons I forgot some careful consideration.

The Host is a Nascar 3D Maglite, so I don't modify anything who is visible outside.

I will use for this size of flashlight the big F-cell Li-Fe do security concerns, for example, "if I leave the flashlight turned on..."

I got a rebel reflector for good throw, the backside ~13mm depper than the old design! I thought "no problem", I can mount the driver between Switch and the two 32900 Li-Fe batteries. I measured the 32900, hell they are each 94mm long! --> no more space for the driver. :(

The mag-switch is shortened on each side, now total 22.5mm height.

The Wichtel 9A-Driver with is described with 13mm height, measured with cables 15.5mm.

If I make the heatsink like the draft, the Cu-heatsink is only 13mm thick, thats problay not enough for a SST-90/SSR-90.


What should I do?

thanks, Peter
 
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yazovyet

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are you able to do a combination of:
a) shortening the tail spring
b) modifying the tail cap so the spring sits deeper in it
This might give you enough room to put the driver between the switch and the batteries. I suppose that may lead to some undesirable wire lengths but I'm not sure. I guess it depends on the size of the wires if 45+mm is too long.

edit:
also, does that diagram show that you have the copper heat sink in an aluminum sleave?
 
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Der Wichtel

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13mm should be enough. The problem is to get the heat away from the Mag itself.
The rebel reflector doesn't fit into the old mag hosts because of their longer threads.
 

zelda

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@yazovyet

The tailcap have a insertion for the o-ring with 32.7mm, who starts at 7.2mm.
Yes the heatsink is made with 2 components, the cu-heatsink will be inserted when the al-pice is heated for a good fit.

@der wichtel

some user reported, its possible to run it up to 10min in a D-host. Okey, probably with a larger heatsink than mine. ;)
 

350xfire

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What is the point of using copper when the whole thing is encased in aluminum? The heat will only be transferred as fast as the worst conductor will allow. In this case the aluminum... So do it all in aluminum.
 

yazovyet

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heat transfer, copper/aluminum vs all aluminum:
Pure copper would be best (thermally) but due to availabillity, cost, weight, or some other reason a copper core was selected with an aluminum (Al) outside.

There is 2 reasons to use partial copper (over pure aluminum).

First, it will have better heat transfer. Copper transfers heat faster than Al, so having some copper is better than none at all. Once we get to the outside of the copper there is more surface area for heat to be tranfered through so using Al is not as big a restriction there. An road anallogy might be that copper is like a 40 mph zone while Al is a 15 or 25. And that as you get further out from the middle, the more surface area for the heat to move through is like having more lanes.

Second, it takes more energy to heat up a given volume of copper than aluminum. So if the user plans to run the light in bursts and let it cool down after, then the copper will allow for longer bursts before needing to turn the light off.
 

ma_sha1

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What should I do?

thanks, Peter


There are very limited room for improvement, only one area I see that could improve:

Make the Aluminum section longer, it doesn't need to be same height as the copper surface, it can extend
about 7mm above the copper surface before touching the reflector, this will give you about 25% more surface
to mag body based on your drawing. This will improve alu. sleeve to mag body heat transfer .

Also, you might want to extend the copper section outer shell all the way down to contact alu sleeve lower half,
better yet, just make a H-shaped heat sink out of copper completely.
 

Slartibartfast

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My $0.02:

I made my copper (C101) heatsink so it's outside diameter was a tight fit to the ID of the Mag, I counterbored the underside for the driver and counterbored the top side for the emitter star. This was done to maximize both the copper mass and the contact area between the heat sink and the aluminum of the mag body. The heat sink butts against the switch on one side and is flush with the top of the barrel on the other. The top (emitter side) has a chamfer place upon it to allow the Rebel deep reflector to sit down properly. Cross sectionally it would look like a blocky 'H'. This has been very effective at running the SSR-90 at 10amps with no blue shift at all.

This with a glass Aspheric makes for one very heavy headed mag lite!
 

PeterH

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Plugging the geometry into a heat sink calculator I've put together (warning: beta software), the capacity of the copper and aluminum to conduct heat looks like overkill. A 5mm copper slug snug inside the aluminum flashlight head should be enough without the extra aluminum piece. The capacity of the head to dissipate heat to the air is more in doubt. My calculator figures ~24deg C/W, but that's easily the least certain output.

As for why copper nearest the LED, that's where the cross section to conduct is least.
 

zelda

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I recalculated the space left & wiring of the driver. It will fit between switch and batteries, so I have around 29mm space! :twothumbs The switch looks now like a skeleton with a lot of wires :)

The origin of the copper/al heatsink is from a Intel i7 stock cooler:
coolerl.jpg

Okay, its made for higher heat dissipation than a SST-90, (Socket 1366-i7 = TDP 130W!) Intel choosed for some reason a big cooper-core, despite the higher production cost. I don't have a source for small piece of copper with 35mm diameter, so I have to make a compromise ;)

I can also build a second heatsink in al for comparison.
 

CKOD

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Should I remove the elox inside the mag tube for better heat transfer?

Translation issue? Are you talking about the anodizing/ aluminum oxide coating on the wall of the tube? If so, leave it, as aluminum oxide's thermal conductivity is plenty high, and the coating is very thin.
 
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