Too Busy For Words - the PaulWay Blog

Tue 17th Apr, 2007

A brilliant realisation

In a bit of idle browsing, I suddenly realised that there's another possibility to save energy when using a home 12V power supply 'rail'. All those halogen lights run off 12V and have 50W plug-packs up in the roof to power them. The plug packs overheat sometimes and switch off to protect themselves, which is a little irritating when you have visitors. But with a 12V power supply rail in the house, you'd just power them directly off the 12V supply, thus cutting out another conversion inefficiency.

The only question that this leaves me with is how to adequately protect the 12VDC circuit against all the things that the regular 240VAC circuits are protected from: ground leakage and short circuit. But this is the matter of a small Google search: there are, of course, quite a few circuit breakers for 12VDC systems. There's even a thread on the Home Owner's Chat forums to the effect that some modern AC circuit breakers are also rated for DC operation. Maybe not the same rating, however, because there's a difference between the RMS power of AC and the direct power of DC. If all else fails, I can probably find a suitably high-rated fuse pack for a car and use that.

There's even plenty of discussion on the question of wiring. The key observation is that there's more of an issue with voltage sag over household distances, but I'm still trying to determine the DC rating of standard 240VAC home wiring. The estimates I've made show that American Wire Gauge 12-14 is considered 'standard' for their 110VAC circuits, so we're probably using AWG 8-10 - for those who prefer metric, that's a cross-sectional conductor diameter of about 3.26 - 2.59 mm. There's a handy voltage sag calculator on-line. It'd be kind of useful to be able to use standard wire sizes, although I think I'd probably spray-paint mine some recognisable colour to indicate which lines were DC and which AC. Helps stop those annoying destruction of costly appliance moments...

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