Extreme Pi cooling

Ireceived what could well be the most expensive item I’ve ever bought in terms of pounds-per- square-inch this month: an active heatsink and fan assembly for the Raspberry Pi.
One of the biggest advantages of embedded CPUs against mainstream chips is that they generate a very small amount of heat, which is only natural considering they also draw considerably less power. The Pi’s Broadcom BCM2835 processor is no exception here: even sandwiched between the PCB and a memory module, the chip requires no additional cooling.

 That hasn’t prevented myself and others from fitting heatsinks, of course. A passive aluminium heatsink, such as the type typically sold for adhering to BGA memory modules, can drop the internal temperature of the chip considerably. Also, it may – or may not – help to prolong its life if you’re venturing into the realms of Turbo Mode or manual overclocking, or enjoying the benefits of living somewhere with a climate a little warmer than sunny Blighty.
When my friend Andrew Back found – and rightly mocked – an eBay auction for an active heatsink with integral fan, however, I knew I had to have one. When it finally cleared customs, I’m delighted to say I wasn’t disappointed: a black aluminium tower heatsink is joined to the smallest fan I’ve ever owned through a piece of heatshrink tubing.
The latter is available in a variety of colours, although sadly, I wasn’t given a choice about which colour I received. The package also includes pigtail connectors that sit on the Pi’s GPIO header.
The advantage of the latter is that they make it possible to run the fan at two speeds, by connecting it to the 5V or 3.3V pins. The disadvantage is that the fan doesn’t fit if you have an add-on board that’s hooked up to the GPIO header. At least, not without snipping off the connectors and doing some soldering.
To test the efficacy of the setup, I set up a Raspberry Pi Model B in 900MHz Turbo Mode, and took readings from the internal temperature sensor. The results aren’t surprising: in a room with an ambient temperature of around 18°C, the bare Pi reported a loaded temperature of 41°C. With the heatsink attached, but the fan disabled, that dropped to just under 38°C.

When connecting the fan to the 3.3V header, the Pi’s internal temperature report dropped to an impressively low 31.4°C. Then, when using the 5V header, the lowest overall temperature of just under 30°C under load was achieved.
Success, then – the gadget works! Now to, wait, what’s that noise? Oh. Small fans, even at low speed, whine. Uncased, it isn’t too bad – roughly akin to coil whine in an old CRT monitor, but putting the Pi in a plastic box with a hole cut above the heatsink amplifies the volume considerably.
As a serious venture, I can’t recommend buying – or building – an active heatsink for a Pi. You’re unlikely to prolong its life by much, it offers nothing in the way of extra overclocking headroom – I could hit 1.1GHz on the test Pi with or without the heatsink – and a passive heatsink is cheaper and quieter.

If you want the ultimate Raspberry Pi cooling setup, though, I can recommend speaking to James ‘Phame’ Couzens on the bit-tech forums (http://forums.bit-tech.net): rather than a fan, Phame designed – as part of a Pi-themed modding contest – a waterblock for the Pi that, as far as I’m aware, is the smallest self-contained water-cooling setup in history. Dubbed the Wet Pi, it’s a jaw- dropping piece of work.

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