Mailinglist Archive: opensuse (1620 mails)

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Re: [opensuse] UPS : replacing battery with 12 volt Jelly Car Battery
On 11/25/2014 8:27 AM, James Knott wrote:
On 11/25/2014 11:20 AM, John Andersen wrote:
A lot of telecom and industrial network equipment runs on -48V DC,
provided by batteries. Also, many server sites run the computers on
high voltage DC, to eliminate the AC-DC and DC-AC conversions. You
could probably modify a typical computer power supply for that, but
you'd need a string of about a dozen 12V batteries to run it. Computer
switching power supplies rectify the incoming AC and use the DC to run
power oscillator at a high frequency that's then passed through a
transformer to be rectified and regulated at the desired voltage. In
North America, that DC would be in the vicinity of 150V.
That's the most tortured description of a power supply I've ever heard.

Transformers do not rectify nor are they used with DC.

I guess I was too brief with a brief description. I was just trying to
point out the stages the power passes through.

AC in > rectify > power oscillator > transformer > rectify and regulate
DC output.

With high voltage DC, the first rectify can be omitted and, if UPS is
used, the DC > AC conversion, in the UPS, is also eliminated.
Eliminating those two stages improves the overall efficiency, which is a
major consideration in a large server site.

You are conflating things that might be outside your computer with
things that are inside it.

Everything inside your computer (beyond the power supply) runs on DC.

With a DC supply, capable of generating 5 and 12 volts, you don't need
anything else.

You can power a 19 volt laptop from 2 car batteries for many days
on end. All you need is a LM7809, which will set you back $1.95 plus shipping.

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