On Mon, 01 Oct 2007 02:58:01 -0700, meow2222@care2.com
wrote:

>kony wrote:

>> >If they only need power the pc for 10 seconds, and are forever on
>> >trickle charge, when in use theyre always going to be fully charged,
>> >under load, and with no charging source running. That gives a much
>> >narrower voltage window. Whether its narrow enough is another
>> >question, as you say.
>> >
>>
>>
>> I would expect it to take a bare minimum of sub-C sized
>> NiCad, if not larger, to maintain the high current required
>> without dipping too far under a stable voltage range.
>> That's at least 17 cells for the 3 major rails,
>
>I make it 10 at nominal voltage, but with the high load current you
>might be closer.

I was speaking of the cells for the 5V and 3.3V rails in
addition to the 12V.
>
>> it probably
>> wouldn't fit in a 5 1/4" drive bay,
>
>I see no probem in getting it in a standard CDROM enclosure.
>Sub-C batteries, dropper for charging, and a little detection
>electronics would fit in half the size.

With Sub-C, yes that would be possible but I was thinking
along the lines of it being fairly expensive just to get a
few dozen seconds of runtime (if that), it would be better
to have larger than Sub-C and then discharge the cells less
to decrease the voltage drop, plus the larger cells
typically have a lower impedance as well. There should
probably be some cutoff circuit for when they fall below a
certain threshold as having the system write to disk when
instable could be even worse than just abruptly shutting off
in some cases.


>Cost depends entirely on sales volume. Eliminating both the mains
>psu and the invertor are causes for a real price drop, but real world
>cost depends as much on business and market factors.

Yes, the cost has almost nothing to do with parts
elimination, only market demand for volume of the product.
You could probably buy a whole CDROM drive and gut it, that
costing less money than it would cost for an empty
electronics enclosure of the right dimensions, for example.


>> It might be most
>> worthwhile when size or weight were the most critical
>> factors,
>
>true, but if it contains much less stuff and costs less it could
>potentially take over market dominance from the current plugin jobs.

I can't see that happening, I wouldn't expect it to run for
over a minute if that long, contrasted with 15 minutes for a
device that can power more than just the computer. Remember
that often people might be actively using the system and may
want the monitor to work, or an inkjet printer or
modem/router/etc. depending on the circumstances. There's
enough of a price disparity between SLA and NiCad that it
wouldn't end up significantly less expensive but would have
significantly shorter runtime (and versatility since it
lacks any 110-220 VAC output).

These other devices could also have their own individual
battery packs but then the cost continues to rise.

Also we haven't even considered the little odds and ends to
implement this, like the wiring harnesses, connectors, etc,
requiring the primary AC-DC PSU to input to this battery
pack for a switchover circuit or else a more crude and lossy
isolation would have to be used.



>
>One could possibly be daring and go with an SLA battery in a
>plastic liner on the basis that by the time its rotted through the
>ups
>case the pc will be 10 years old and of little value anyway. A mini
>SLA would be cheaper than NiCds.
>
>Using NiFe would enable even smaller cells.
>
>
>> though Li-Ion cells might be even better for that
>> if the budget stretched to cover a more sophisticated
>> charging circuit. Enough Li-Ion cells & current capability
>> might fit in a 5 1/4" bay space.
>
>If you up the price its range of application dwindles, and small
>sales
>volume equals high price - just not the way to go imho.
>


I think we'd already reached that point when the
conversation about an internal battery began. It's not as
though the tech to make it happen didn't exist, it's that
nobody perceives a large enough market for it to make it
practical. There may well be such a device that already
exists but that it's priced itself into obscurity already.
I vaguely really I saw some power supplies somewhere that
were half-height internally (I mean std. ATX form factor)
and had a layer of Ni-Cad batteries under the PCB. The main
problem with that today is the ever increasing current
requirements of modern systems, there's just not enough
empty space in decent ATX PSU for this today.