Last month’s Publisher’s Letter about the possibility of DC power in the home triggered off quite a response from readers. Some raised the obvious safety issues of the difficulty of safely switching high voltage DC and the possibility that a DC shock can be more dangerous than AC. These drawbacks must be admitted. Others though, saw the potential in the idea and went on to expand the concept.

My feeling is that most people have such a reliable 240V AC supply that they would never contemplate ever having any other system; it works, why fix it? For those that do have an unreliable mains supply, and I include myself in that category, the occasional inconvenience might be extremely irritating but it would not justify the in-vestment and time necessary to eliminate it. And whether a DC power system would be the way to go would probably be a moot point.

However, for those who are in remote locations far away from any mains power supply, a combination high and low voltage DC system based on solar arrays could be made to work. As one of our readers points out in the Mailbag pages this month, quite a few appliances could be made to work on DC. But would it be safe?

Now that the problem of high voltage DC switching has been highlighted, could be it be overcome? The answer is yes. But it would not be necessary to have large mechanical power switches to turn the appliances, lights or whatever, on and off. The logical approach would be to have electronic switching which could cope with high voltage DC and AC. This would be pretty straightfor-ward, when you think about it.

After all, many appliances these days do not rely on me-chanical on/off switches; they use electronic switching. Virtual-ly any appliance which comes with a remote control uses electron-ic switching. The same point applies to microwave ovens, many washing machines and dishwashers. An electronic switch based on a power Mosfet or IGBT (insulated gate bipolar transistor) could be made to handle the switching job for AC and DC. So a compact, reliable and rugged power switch is not an insurmountable prob-lem.

Nor is the problem of automatic degaussing for TVs and computer monitors running from DC insoluble - there has to be an electronic solution.

So as I remarked last month, there is no reason why most appliances could not be made to run on 250V DC. Will it ever happen? Probably not.

To be realistic, if you were faced with providing power in a remote location, the most practical approach would probably be to power as many appliances as possible at 12V DC and for those that cannot be run from low voltage DC, use a 12V DC to 240VAC inverter which would only run when an appliance was switched on. Many of the bigger inverters already have an auto-sensing feature and it is very worthwhile because it stops the inefficiency of running inverters continuously.