UPS for FreeBSD

[Erich Dollansky]

Hi,

On Mon, 1 Dec 2014 12:39:24 -0500
Alejandro Imass <aimass at yabarana.com> wrote:

> On Sun, Nov 30, 2014 at 12:33 AM, John Johnstone
> <jjohnstone at 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