Given the way things are, we are stuck with different styles of power plugs for the different mains voltages. With some clever design, this problem could be turned into a solution. One could have a power cord with a mains end and an appliance end, with connectors that are not standard mains connectors. The 120V power plug would function as the appliance end connector for 240V operation, and the 240V power plug would function as the appliance end connector for 120V operation. For safety, the power plug would not connect to the power cord on the appliance end until the plug was captive in the appliance. No special circuitry needed to switch voltage ranges.
There is another solution for simple resistive appliances with an even number of heating elements: A DPDT relay with the coil wound such that it is able to switch the contacts only if the voltage is sufficiently high. It would switch the heating elements between series and parallel connection. This is about as "unsophisticated" as I can be. Cheers, Donald Borowski Senior EMC Compliance Engineer Schweitzer Engineering Labs Pullman, WA, USA From: "John Allen" <[email protected]> To: <[email protected]>, <[email protected]> Cc: "'Pete Perkins'" <[email protected]> Date: 05/07/2013 12:16 PM Subject: RE: [PSES] UL warning regarding a wall receptacle Sent by: [email protected] But then you do have to ask the question: for those appliances which are purely ON or OFF like a toaster, a water-boiling kettle or a simple radiant electric fire, what is the point of including ?sophisticated? circuitry just to switch between voltages ? and probably adding considerably to the cost of the appliance compared with one without the switching function (and these are typically dirt cheap products sold on price point as much as anything else). Therefore I think that the day of the ?universal voltage appliance? is still a LOOONG way off for products like these J - especially for markets (like the USA) where ?universal voltage sockets? are rarely, if ever, likely to be seen (thankfully!). John Allen W.London, UK From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: 07 May 2013 19:30 To: [email protected] Cc: Pete Perkins Subject: RE: [PSES] UL warning regarding a wall receptacle But breakfast would take four times longer: P = E²/R If R is fixed, and voltage E is reduced by a factor of 2, then power P goes down by a factor of 4. A more clever design with two heating elements would put those elements either in series or parallel, depending on the voltage, and operate at the same power in either case. Donald Borowski Senior EMC Compliance Engineer Schweitzer Engineering Labs Pullman, Washington, USA From: "Pete Perkins" <[email protected]> To: "'John Allen'" <[email protected]>, < [email protected]> Date: 05/06/2013 08:52 PM Subject: RE: [PSES] UL warning regarding a wall receptacle Sent by: [email protected] John, I agree with your comment in today's environment but the implementation of the required 'green' technology will require almost every household and commercial electrical product to run from a SMPS. (Well maybe a dumb toaster won't require it, but it could be designed to run on 230V and then take twice as long to make the breakfast toast in those countries using 115V.) Everyone wants smart technology everything so this new scenario should come about rather quickly (maybe in a generation or less). The customer won't care what the system voltage is; perhaps the power company could find clever ways to take advantage of this and relax their system voltage regulation requirement. Or maybe it won't be the power company controlling this but, rather, the smart grid taking power from all the neighbors renewable energy stations and sharing it locally. Should be an interesting time; by then we will have learned more about both protection and operation under these broader V conditions - brownout saver circuits for the low end and better OV protection on the other. It looks like fun times are coming to a power system close to you. :>) br, Pete Peter E Perkins, PE Principal Product Safety Engineer PO Box 23427 Tigard, ORe 97281-3427 503/452-1201 fone/fax [email protected] - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
