From owner-freebsd-questions@FreeBSD.ORG Mon Dec 1 05:16:26 2014 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 792223A7 for ; Mon, 1 Dec 2014 05:16:26 +0000 (UTC) Received: from mario.brtsvcs.net (mario.brtsvcs.net [199.48.128.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 45860D77 for ; Mon, 1 Dec 2014 05:16:26 +0000 (UTC) Received: from chombo.houseloki.net (c-71-59-211-166.hsd1.or.comcast.net [71.59.211.166]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mario.brtsvcs.net (Postfix) with ESMTPSA id BFBFB2C160E; Mon, 1 Dec 2014 05:16:18 +0000 (UTC) Received: from [IPv6:2601:7:2580:674:baca:3aff:fe83:bd29] (ivy.libssl.so [IPv6:2601:7:2580:674:baca:3aff:fe83:bd29]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by chombo.houseloki.net (Postfix) with ESMTPSA id E2952176A; Sun, 30 Nov 2014 21:16:15 -0800 (PST) Message-ID: <547BF99D.3070801@bluerosetech.com> Date: Sun, 30 Nov 2014 21:16:13 -0800 From: Darren Pilgrim Reply-To: freebsd-questions@freebsd.org User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: RW , freebsd-questions@freebsd.org Subject: Re: OT: UPS for FreeBSD References: <54777AB1.9010800@bluerosetech.com> <54779629.302@bluerosetech.com> <5478BD4F.7020306@yahoo.com> <5478BEE6.30308@bluerosetech.com> <5478CC08.9090307@yahoo.com> <20141128204722.561f948e@archlinux> <5478F16A.80605@yahoo.com> <54791d3a.w/pI0kak03d+3nKC%perryh@pluto.rain.com> <20141129113405.3d1bd1d6@X220.alogt.com> <54798883.saa13h6lE6rPwZCf%perryh@pluto.rain.com> <20141129113018.17759e2a@archlinux> <547a52e9.tCBMi6xWobou5Fcd%perryh@pluto.rain.com> <547B7093.1020305@bluerosetech.com> <20141130210305.2d62bbb1@gumby.homeunix.com> In-Reply-To: <20141130210305.2d62bbb1@gumby.homeunix.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 01 Dec 2014 05:16:26 -0000 On 11/30/2014 1:03 PM, RW wrote: > On Sun, 30 Nov 2014 11:31:31 -0800 Darren Pilgrim wrote: >> An unloaded, ideal, single-phase FWR produces Vdc = 0.900Vrms. The >> factor is 2sqrt(2)/pi, to be precise. A half-wave rectifier produces >> half that. > > That's the mean voltage, which is of limited relevance. The mean voltage is the output DC voltage. >> From where did you get your figures? > > He's referring to a rectifier charging a smoothing capacitor; the > voltage will rise to sqrt(2)*Vrms. No, the voltage across the capacitor will rise to 0.900*Vrms. Look at it this way: The output of the diodes is a time-varying (AC) signal with a DC offset. The cap provides a low-impedance path for the AC signal, turning the voltage cycle into a current cycle that accumulates a charge in the cap. Once the cap is fully charged, it fully negates the AC component and you're left with just the DC offset of 0.900*Vrms. > He's added on an unnecessary factor > of two - possibly because he's mixing it up with a bridge-rectifier in a > centre-tap configuration. A bridge rectifier doesn't use a center-tapped transformer. You wouldn't see 2*Vpeak in a two-diode rectifier either. The voltage between the center tap and either diode tap is at most Vpeak.