Replace fan with heatsink on repurposed laptop?

edselfordfong

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Apr 24, 2009
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I want to repurpose an old laptop I have. I plan to ditch the monitor and keyboard, and replace the fan with a heatsink for quiet. I'd put the whole ugly mess in a wood box, cutting plenty of holes for air.

The chip is a Intel Pentium M 740, 1.73GHz (single core mobile chip). I will use this as a networked headless music server with a USB sound card. Basically, all it'll be doing is playing music, which is a very light load on the chip.

My question is: can I get by without a fan? There are just a handful of passive socket 479 heatsinks available.

I've only ever built a conventional desktop rig, so I know very little about cooling. Here are the specs on the best heatsink I found:

- Model number: Nexus PSM-5000
- Socket 479 (Pentium® M, Celeron® M, Core Duo, Core 2 Duo)
- 2U, size: 50x50x47mm
- Fin pitch: 1.6mm
- Fin thickness: ~0.44mm
- Passive SkiveTek® heat sink
- Full copper, 99.5% pure, C1000 copper material
- Thermal resistance: 1.060°C/W
- Weight: 265 gram

This one has a little brother, which is the same except that it's 1U and has a slightly higher Thermal resistance (1.077°C/W).

These look like what I need, but the manufacturer says these... "are designed to operate in an environment with a good thermal/cooling structure. Although the cooler is passive it does require an amount of airflow to go through the fins to be able to provide the neccessary cooling. So the fins of the passive cooler should be inline with the airflow direction in the case for optimal performance"

Can I ignore that, as long as I put a lot of holes in my case?

If it turns out that I do need a fan, can I plug in a large, quiet desktop fan into laptop fan's power source on the motherboard? Are there power jack adapters for that, or would I have to jerryrig something? Would the power specs be compatible?

(unrelated bonus question: is there any advantage to ditching the hard drive and running this thing from a usb flash drive? I just like the idea of no moving parts, but there might not be much of an advantage to doing this.)

thanks!
 

r_manic

Administrator
Well, I'm not comfortable running everything on a flash disk. (Perhaps unfounded) reliability concerns aside, where will you get a big enough flash disk to hold everything you need?

Regarding your cooling idea, I don't think there will be a problem. Like you said, all this thing will do is play music, so I guess your CPU won't heat up too much. But just to be on the safe side, you can place that quiet desktop fan on the side, just to keep the air moving inside, making sure the heatsink continually radiates the heat into the wind.
 

edselfordfong

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Apr 24, 2009
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thanks for the reply!

will I have trouble hooking up a desktop fan to a laptop mobo?

as for flash disk, it would just be for the lightweight linux OS. All the music would be on the network. I don't think there would be much writing to the drive, and if it failed, I guess it would be pretty replaceable. It's not like I'd have anything important on it, since this is a dedicated music player.
 

orangegator

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Mar 30, 2007
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Laptop cpus are low power, low heat. As long as you can mount the heatsink properly, you should be fine running passive. I'd be wary trying to plug a large desktop fan into a laptop fan plug, as they draw more power. You could wire an adapter to plug the fan into a usb port. It'll run very quiet at 5V.
 

r_manic

Administrator
Ok, since you put it that way edsel, reliability on a flash drive is definitely more sensible.

You can also try running everything passively first, then watch the temps. If they're too high for your taste, that's when you can try the desktop fan. Let us know how it goes!