Tuesday, March 6, 2012

DC Power

            DC POWER                                        APRIL 2010

There has recently been a revival of interest in DC (direct current) power as a way of distributing electricity to the home. Current systems all use AC or alternating power, though some of the early experiments in electric power systems did actually use DC.

Briefly, AC is used because it allows voltage to be transformed (fairly) easily from very high voltages down to household voltage levels. High voltage is used because the amount of power lost in transmission is less with high voltage than with low.

Now that the U.S. in particular is considering major extensions to its electric supply grid, there are suggestions that DC power could be more efficient. I don’t really want to get into the details of why, partly because I don’t know; and anyway that is not what I want to talk about here.

What I want to look at is the possibility of having DC power in the household. At present, all our wall power sockets deliver AC. This isn’t too bad for white goods like cookers, heaters and so on, because they use quite a lot of power, and can utilise the 220/110 volt supply quite well.

But of course nowadays the vast majority of devices that we plug in to our power sockets are electronic. In our house in the UK, we have 5 TVs, 4 DVD players, 2 old VHS ones, 1 old HiFi system, 1 digital radio, 1 desktop PC, 2 printers, 1 photo printer, 2 laptops, 1 netbook, 1 ADSL router, 1 burglar alarm, 3 cordless phones, 3 phones, 1 fax/phone,  and 3 clock radios.

Then of course, there are the chargers for 3 mobile (cell) phones, 1 satnav, 1 ipod, 1 PDA, 3 digital cameras, 1 camcorder, 2 rechargeable torches, 1 battery charger, 1 cordless drill, and 3 cordless shavers. And I’m sure I’ve forgotten a few things. Oh yes, 1 digital heating controller.

That makes a total of 50 electronic devices – far more than the white goods that really benefit from AC power. Because nearly all this electronics actually needs low voltage DC power. The crazy thing is that every single one of these devices separately converts the high(ish) voltage AC power down to low voltage DC power before it can use it.

Lighting still uses AC power, although trends to halogen downlighters and mini spotlights is changing that quite a bit. Many of these run on 12V power which again has to be transformed down.

Because there are so many chargers made these days, they are fairly cheap. But still, it does seem a backwards way of doing things. Wouldn’t it be nice if you could just plug these things into a DC power socket that was suitable for them. Just think, no more searching for the right charger for that phone, MP3  player, camera…

Now there are a few snags. All these things don’t use the same voltage; some use around 3V, some 5, some up to 12. But this is partly because they all have to convert their own AC to DC. If there was a standard for supplying DC to the home, most devices could use it directly. Or maybe there could be a 2 value supply. Wiring low voltage low power around is much easier than existing house supplies; the wire can be thinner, and there is no safety issue.

Some devices, like large screen TVs, take quite a bit of power, and to supply these would need heavier duty wiring; or maybe it would be best to leave these as AC powered devices.

So DC power would not replace the existing AC power in the home, but it could quite easily be added to the AC power cabling when a house is built. Already houses are being fitted out with cabling for TV, phone and PC networking. It would not be too difficult to add one or two wires carrying DC power from a central power supply.

Of course this would mean a big change in the way some electronic devices are made and sold, with a DC power input socket. Still, as mentioned already, many small devices like phones have these already. Even the ability to plug these into a wall socket instead of a charger would be an advantage. And it would force some standardisation into the market; it seems crazy that there are so many different chargers all doing very much the same thing.

It might even make companies think about standardising lithium ion batteries in rechargeable devices – wouldn’t that be great? We used to have standards for batteries – AA, AAA, C etc. Now every rechargeable device has a slightly different one inside – great for the manufacturers of course because they can charge a high premium for the battery. Not good for the consumer, or in the long run for everyone.

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