Mailinglist Archive: opensuse (1620 mails)

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Re: [opensuse] UPS : replacing battery with 12 volt Jelly Car Battery
On 11/25/2014 01:46 PM, James Knott wrote:
On 11/25/2014 01:33 PM, Anton Aylward wrote:

The computer has an internal power supply that converts the more or less
standard input voltage to what's required by the computer. This also
includes voltage regulation to ensure the equipment runs properly.
Otherwise, you'd need a battery that provides 5V and another for 12V and
then try to keep them both charged by the same amount.

It doesn't quite add up.

If there is a stabilized 12V supply then that can drive the part that
needs 12V and *also* drive a step-down to 5V.

Computer power supplies typically have multiple outputs at different
voltages. It's not that hard with modern tech.

I know that. Re read what I said. There's an "also" in there.

Its a few years since I had to design one of these but I can't imagine
the principles have changed, just the available parts.

Actually, you're losing very little. Unlike linear regulators,
switching supplies are very efficient.

Yes I know all this, so big snip.

Switching supplies are
also very tolerant of input voltage variations. This is why the same
power supply can often be run off 120V or 240V.

Yes, but that's NOT what I'm talking about.

I'm assuming the switcher has already stepped down from the 120/240 to
the 19VDC.

Its what's INSIDE the laptop that I'm talking about.

The only explanation I've found is that the 19V is used in charging of
the Lithium-Iron cells. That have a charging voltage of 4.2V and ganged
to 4 that makes 16.8V ... Give some headroom and get 19V.

Some computers have optional battery packs, with a different number of
cells and terminal voltage.

Yes I'm aware of this too.
My HP came with a 6-cell and there was an option to upgrade to an
8-cell. My phone has a similar, but there the "extra" cells make a
bulge at the back and needs a new case-back and will no longer fit in my
hip pouch.

But if you are running the laptop without an internal battery, that's
not an issue.

So here we come down to what I was originally asking about.

The power-brick switcher is external to the laptop and the batteries
have been removed, so its just the 19VDC input. Can we pleas stop
talking about the things that are now external to the laptop chassis/case?

The question was "why 19VDC?"
That meant
why, since the electronics run on 5VDC or less
and _maybe_ the disk motor needs 12VDC
and _maybe_ the DVD burner needs 12VDC
is the thing being supplied with 7VDC over its obvious need?

One explanation was battery charging.

Take the battery out and what need is there for more than 12VDC?

Take the DVD burner out and run on a 5VDC SSD and what need is there for
the 12VDC?

Why can't I run a laptop on a 6VDC motorcycle battery?

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