Date: Sun, 30 Nov 2014 21:16:13 -0800 From: Darren Pilgrim <list_freebsd@bluerosetech.com> To: RW <rwmaillists@googlemail.com>, freebsd-questions@freebsd.org Subject: Re: OT: UPS for FreeBSD Message-ID: <547BF99D.3070801@bluerosetech.com> In-Reply-To: <20141130210305.2d62bbb1@gumby.homeunix.com> References: <CAHieY7QGp2ELF-R91eu=vSrPsimVmVNJQ4kfucQ56PR7EEZmig@mail.gmail.com> <m57qdq$did$1@ger.gmane.org> <54777AB1.9010800@bluerosetech.com> <m581p1$65m$1@ger.gmane.org> <54779629.302@bluerosetech.com> <alpine.BSF.2.11.1411271433320.60866@wonkity.com> <5478BD4F.7020306@yahoo.com> <5478BEE6.30308@bluerosetech.com> <5478CC08.9090307@yahoo.com> <20141128204722.561f948e@archlinux> <5478F16A.80605@yahoo.com> <CABhTyc9m7fOoeV170dj=foAhmyYWphzc8KD8wBacu5gNRPhT%2BQ@mail.gmail.com> <54791d3a.w/pI0kak03d%2B3nKC%perryh@pluto.rain.com> <CAHu1Y71vVbdx6Yd1VbE7kb_8k9O5UG93RXEaORPU0tULCpMsCQ@mail.gmail.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>
next in thread | previous in thread | raw e-mail | index | archive | help
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.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?547BF99D.3070801>