Date: Tue, 2 Dec 2014 10:38:47 +0800 From: Erich Dollansky <erichsfreebsdlist@alogt.com> To: Alejandro Imass <aimass@yabarana.com> Cc: John Johnstone <jjohnstone@tridentusa.com>, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: UPS for FreeBSD Message-ID: <20141202103847.564806a2@X220.alogt.com> In-Reply-To: <CAHieY7QqeUGUiOfMZyOkVkunWyBO7izX=a_2rxYgu1eYrmBhgA@mail.gmail.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> <54789AF3.7090100@yahoo.com> <547AAC20.1050006@tridentusa.com> <CAHieY7QqeUGUiOfMZyOkVkunWyBO7izX=a_2rxYgu1eYrmBhgA@mail.gmail.com>
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Hi, On Mon, 1 Dec 2014 12:39:24 -0500 Alejandro Imass <aimass@yabarana.com> wrote: > On Sun, Nov 30, 2014 at 12:33 AM, John Johnstone > <jjohnstone@tridentusa.com> wrote: > > Why do switching power supplies really care about the input wave > form? Most switching power supplies rectify with a full bridge and > capacitors and then switch from that rectified DC so why would it > care about the incoming waveform? So long as it's oscillating, > square, sine or triangular should work just the same. > the average volage over a square is much higher than over a sine. If the components are not designed for this, they will fail. You can see this effect by connecting a light bulb to an UPS and switch mains off an on again. The smaller the difference in brightness gets, the better the UPS emulates a sine. Of course, the life time of the light bulb gets reduced. > I think HF components would get filtered by design in the first few > stages of the switching PS so I don't understand why pure, or close > to pure sine wave is really important. What components are really at > risk from poor sine-wave inverter? Besides, UPS are designed to power > the equipment for a short period (either to shut-down or activate a > backup generator), so in reality there is that much more risk by > using a cheaper UPS? IS the price difference really worth it? > This is the question. Most power supplies will be able to handle the square waveform. Escpecially modern power supplies being able to handle any voltage from 100 to 250V. > Or is it all technical mumbo-jumbo to charge a lot more for "pure sine > wave", which honestly does NOT need sophisticated components like > someone said. It can be accomplished with a simple saw-tooth (with 2 > OP-Amps one as integrator and another one as comparator) and a > low-pass filter (a coil of wire). Inverter circuitry is really not > that complex and good sine-wave approximations are not that hard to > do. I am pretty sure a typical switching PS will do just fine if you > feed the square wave or an unfiltered saw-tooth sine wave into it. > It is the volume. When the cheaper UPSes appeared, their price advantage was pretty minor. I wonder meanwhile if it is not cheaper to use an inverter used in solar panel installations. At least for larger inverters, they have a clear price advantage but require batteries which are not available at the next corner shop. Erich
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