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Bath switches from AC to a DC computer network

The University of Bath has invested £80,000 in switching its library's network of computers from AC to DC, in the attempt to reduce energy consumption. Later, the system -- which will act as a showcase for this type of project -- may run on wind or solar power, both of which generate DC rather than AC power.

The University of Bath has invested £80,000 in switching its library's network of computers from AC to DC, in the attempt to reduce energy consumption. Later, the system -- which will act as a showcase for this type of project -- may run on wind or solar power, both of which generate DC rather than AC power.

Computers and most components already run using DC (direct current) rather than AC (alternating current), and typically use a power supply to switch AC mains down to a low-voltage DC. This wastes some energy, and generates heat. However, it is possible to modify PCs to run on DC, and laptops run from DC batteries. Bath's network works in a similar way, with the PCs being powered by a central battery bank.

Large-scale battery storage does have a couple of advantages. First, the batteries can be recharged overnight, when AC power may be cheaper. Second, if the mains supply fails, the batteries will keep the system running for up to 8 hours.

However, Benjamin Williamson, a PhD student and Knowledge Transfer Fellow for the project, says:

"Installing the new system was not a small task, with fifty new DC adapted computers installed overnight to reduce disruption on campus, while the project team moved the one tonne AC converter through the University library and into the roof space, removing and rebuilding walls to transport it."

There must also have been some rewiring involved in changing the power distribution to the PCs from AC to DC. Presumably this was done by running DC lines alongside the current AC mains cables.

Bath's system is similar to powering a network from a large-scale UPS (Uninterruptible Power Supply) but without the losses from frequent switching. In a UPS, mains AC is converted to DC then stored in a battery. This is converted back to AC for transmission to the PC's power socket, then the PC's transformer converts it back to DC for final use.

The DC network will now be evaluated to see if it delivers worthwhile financial and environmental benefits. (I certainly hope they factor in the cost of the time lost/saved due to decreased/increased performance.) However, Miles Redfern, from the Department of Electronic & Electrical Engineering, says: "We have already received interest in the project from a number of corporations running large-scale computer networks who could benefit greatly from installing a similar system."

It seems unlikely that the university is correct in claiming that this is "Britain’s first local DC computer network installed on campus". Comments to a previous article suggest that Manchester University and UMIST had battery-run systems several decades ago and there may well be other examples.

Also, DC computing remains of great practical interest in some areas, including boat-based computers and embedded computers for outdoor signage. UK-based Aleutia supplies DC systems for use in those sorts of application and also in Africa. Company co-founder Mike Rosenberg says:

A lot of what we do in Africa and the basis of our Solar Classroom in a Box (which we've deployed in Kenya and will soon deploy in Nigeria) is pure DC: solar panels connect to a charge controller which lets you charge up a bank of 12V deep cycle batteries and simultaneously use them to power a 12V DC monitor, 12V DC diskless solid state T1, and 12V X1 serving as an LTSP server. It gets a bit trickier because you have to regulate the voltage but you avoid the cost of an expensive pure sine wave inverter."

No doubt many large companies could learn a lot from the University of Bath, but maybe the University could learn things from Kenyan schoolchildren….

@jackschofield

Footnote: ZDNet UK reviewed the Aleutia E1 in 2008.

https://www.youtube.com/watch?v=euVYrsdbyaI Solar Classroom in a Box, Fanless DRBL Server