On Wed, Nov 22, 2006 at 06:58:13PM +0100, Huib van Wees wrote: > On 11/22/06, Zeeshan Zakaria <[EMAIL PROTECTED]> wrote: > Why Aastra phones use more electricity, i.e. 48VDC whereas other > phones use much less, e.g. Grandstream and Linksys both use only > 5VDC. I first thought it was because of PoE, but the ones with 5VDC > also run fine on PoE. What is the difference in power consumption > then? > 48V is also a sort of "standard" for telco devices.... if I remember it > correctly...
Power is nothing to do with voltage (well it is, but not alone), you need the current too i.e. V * A. Pylon electricity lines run at very high voltage (several hundred thousand volts) or the current going down the lines would heat the cables and you'd lose a lot of power. 48V is just a telco standard, and most telco equipment (that runs in racks) is 48V. Probably because 110 (or 220/240 here in EU) is enough to electrocute an engineer, and 5V/12V would require too many Amps so wiring would have to be huge to carry the current. Steve -- NetTek Ltd UK mob +44-(0)7775 755503 UK +44-(0)20 79932612 / US +1-(310)8577715 / Fax +44-(0)20 7483 2455 Skype/GoogleTalk/AIM/Gizmo/Mac stevekennedyuk / MSN [EMAIL PROTECTED] Euro Tech News Blog http://eurotechnews.blogspot.com _______________________________________________ --Bandwidth and Colocation provided by Easynews.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users