Fullscreen HTML5Med Res (??MB)HTML4

PUBLISHER’S LETTER www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Ross Tester Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Rick Winkler Phone (02) 9979 5644 Fax (02) 9979 6503 Mobile: 0414 34 6669 Regular Contributors Brendan Akhurst Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $69.50 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip DC power in the home; would it make sense? If you refer to the battery backup project for cordless phones in this issue, you will see that I am plagued by blackouts in my home. That this should be the case in 1999 in an old estab­lished Sydney suburb is pathetic but there you are. But it got me thinking about ways to avoid the problem, assuming that it will continue into the future. In my home we can at least continue to cook during a blackout since we have natural gas but all other power-assisted activities must cease for the duration of the power failure. So you start to think about pro­viding household power which does not involve the big power items such as heating and cooking. Leave out refrigerators and washing machines which use induction motors and you are not talking about huge amount of power to be provided by batteries. Let’s say we decided we were going to limit the number of lights to several hundred watts and then we are left with equip­ment such as VCRs, TVs, computers and a host of plugpack-powered devices which run from low voltage DC. Perhaps we are only talk­ing about five to six hundred watts or so. Question is: what sort of inverter would you use? Most people would think of sinewave or modified sinewave inverters but perhaps they are not needed. Why not just have a 12V to 250DC inverter? It would be much simpler and more efficient than an AC inverter. Let’s face it: most computers, PC monitors and TV sets will run from 250V DC without any need for modifications. The DC would feed via the existing bridge rectifier straight into the switch­mode power circuitry. And incandescent lamps and compact fluores­cent lamps will happily run from 250V DC as well. That leaves just the plugpack-powered devices (heaps of them, it seems) running at 12V or so. But why would you run them from an invert­er? Why not run them at 12V DC? So the solution would be to run the TV, computer and lights at 250V DC and the lower powered devices at 12V DC, straight off the same battery bank that supplies the inverter. In effect, you would get rid of all plugpacks and run from 12V DC permanently. You would have an automatic contactor in your switchboard to switch from 240VAC mains power to the inverter’s 250V DC and you would run a 12V DC supply around the home for all the low voltage gear. There would be a small bonus too because you would elim­inate the inefficiency of running quite a few separate plugpacks. Mind you, current audio equipment, VCRs and conventional fluorescent lights will not run on DC so an AC inverter would still be required but there is no reason why future models with switchmode supplies could not run on 250V DC as well. What would be the cost of all this, to eliminate blackout-induced frustration? By the time you added up the cost of deep cycle batteries, a big inverter and all the electric wiring modifications that would be necessary, you could be up for $4000 or more, so it is hardly practical just to stop the occasional blackout is it? But a similar problem is faced by many people in remote locations who don’t have the luxury of mains power. They probably think in terms of solar panels, big batteries, DC to AC inverters and so on. Maybe the DC approach, low voltage and high voltage, is a better way to go. In some ways it would be a reversion to the early days of electricity before AC power transmission became universal. It is an intriguing thought, even if it doesn’t solve the problem of nuisance blackouts. Leo Simpson