Mailinglist Archive: opensuse (2496 mails)

[James Knott <james.knott@xxxxxxxxxx>]

Carlos E. R. wrote:
> On Monday, 2008-12-01 at 15:58 -0500, James Knott wrote:
>
> > used to work.  On these, the incoming AC ran a motor, which turned
> an alternator & 8 ton flywheel.  When the power died, a clutch would
> connect the shaft to a diesel engine.  The flywheel started the
> diesel, while maintaining speed for the alternator.  One disadvantage
> to this system, was the output power was slightly lower frequency than
> the input, which caused the real time clock in some computers to run slow.
>
> That can be overcome.
> You have the same setup, but the output of the alternator feeds a
> rectifier-inverter setup, which maintains frequency and voltage while
> there is enough speed left in the flywheel (as the speed gets lower,
> the current increases to compensate).

This was an old system, going back decades.  I don't think it's there
any more.  Regardless the frequency slip was due to the fact that
induction motors run a bit below power frequency.  It's simply the
nature of the way they work.
> > In that same building we also had some turbine & diesel standby (not
> UPS) power and a huge battery type UPS.  There were also banks of
> batteries & rectifiers supplying about 7000 amps @ 48V for all the
> telecom gear. (There were other batteries supplying +-60V and 24V
> power)  This was in a telecom central office that also housed the Air
> Canada reservation system and several other message switching computer
> systems. There were so many large batteries that some of the floors in
> that building had to be specially reinforced.
>
> Most telephone equipment are fed directly from batteries at 48 volts,
> so they don't need inverters, nor UPS fast takeover and such things.
> If computers used the same setup, replacing the 120(230) volts power
> supply with a 12 or 24 volts DC power supply, some things would be easier.

Most of the telecom gear was supplied from the 48V supplies.  Some
servers, intended for large installations, can run off high voltage
> 150V DC.  The purpose of this is to reduce the losses in power supplies
in UPS & computers, as well as resistance losses in the cables.
> In fact, I did see a computer power supply with a 12v dc input some
> years ago. I thought I would see more of them, but that has not been
> so. I wonder why :-?

> From a technical view point, it wouldn't be difficult to modify a
computer power supply to operate from DC, at a voltage that's similar to
what that supply creates from AC.  In computer power supplies, the
incoming AC is rectified to some DC voltage.  That DC power is then used
to run an inverter that converts it down to the voltages required by the
computer.  If you supply the appropriate high voltage DC, you can bypass
the AC input & rectifiers.  Such a supply could be easily designed to
run off 12V.  You might be able to find some with Google.

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