Novena project!

Post date: Apr 17, 2015 12:16:25 AM

I'm the proud owner of one of bunnie's open-source laptops, the Novena. It's a 1.2 GHz quad-core ARM computer with 4GB of RAM and all the other things you'd expect from a laptop (USB, SATA, batteries, a screen, ...), plus some extras (the TTL UARTs are what I'm mostly excited about, but there's also an FPGA, GPIOs, and a software-defined radio module).

Anyway, the big problem with this laptop is that it isn't... the screen is backwards. I guess bunnie likes this, but I don't. So I'm working on fixing it by machining a proper case.

But first, the CPU has a little problem... it likes to overheat. A lot. I suspect this is mostly due to having a dinky heatsink with no airflow, exacerbated by being attached to the CPU with tape (thermally-conductive, I assume, but still probably worse than proper thermal compound). Since the case I'm working on will be aluminum, why not use that as the heatsink? Then it just becomes a matter of moving the heat from the CPU to the case. Enter heatpipes. These are copper tubes filled with water(?) under low pressure. The water boils (at low temperature) at one end- the CPU- then condenses at the other, effectively transferring the heat.

How well does it work? Well, here's my setup:

The heatpipe is held against the CPU with a chunk of 1/8" aluminum I drilled a couple holes in. It also has some thermal compound at the interface between the two. Then it just runs off into space. I set a heatsink from an old GPU (FX5200, I think) on top of he heatpipe, but it's not really attached. There's no thermal compound, and probably minimal physical contact. Regardless, the CPU seems to top out at 53°C when all four cores are running full-tilt, which is fine by me. It took maybe 20 minutes to get there.

With the original heatsink (not shown because I'm too lazy to take more pictures), it would hit 80°C in about a minute (and want to shutdown shortly thereafter). I'm calling it a victory. We'll see how well the chassis I make works as a heatsink (with proper thermal compound and a proper adapter to connect it to the CPU), but it's looking good for passive cooling.