On Mon, 01 Oct 2007 11:13:37 -0700, meow2222@care2.com
wrote:

>kony wrote:
>> 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.
>
>Tap those off the 12v pack, no need to duplicate.

To arrive at ~ 5V alone it could be done, but to remain at ~
5V under high current may not be so easy with sub-C cells.



>
>
>> >> 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.
>
>IIRC radio control enthusiasts use NiCd D cells to run 60A motors,
>and half that would be enough for a PC.

The motors don't care if the voltage drops while a PC does.
Running a pack with a tap in it to derive 5V and 3V power
might be too much current to keep voltage up. Even so, D is
definitely an improvement and yet getting ever closer to
exceeding available space in a drive bay. Remember it's not
just the batteries but the circuit, insulating material or
standoffs, the incoming and outgoing connectors or wiring
harness.

>> 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.
>
>Maybe so, though I assumed most folk just wanted to avoid losing
>data on sudden power down. Even if its 50/50 that would still give
>such a mini-ups half the potential UPS market - but perhaps theyre
>bought mainly for other jobs.

Some might only need to avoid losing data, but how many
would take a device with lesser versatility and capacity
just to save a bit of space outside of the PC while taking
up space and having to route a second thicker wiring harness
inside the PC? There's also another problem in that PC PSU
with rail sense leads use these to sense at the ATX
connector under the presumption it is plugged into the load,
while the resultant voltage at the load will be lower than
it senses due to the intermediate stage of having to go
through the battery pack subcircuit.


>> 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
>
>I think we may have been talking at cross purposes then. I was
>proposing doing away with all that, just trickle charging the battery
>pack from the PC's molex connector. Would need nothing more
>than a basic bottom price linear regulator.

Pack input isn't the problem, that'll work for charging but
you still need to isolate the two supplies from each other.
You have two power sources and you have input to the pack
through this regulator, but it still has to get to the
motherboard without being a common rail to the PSU, and both
have to be plugged into everything so the original PSU plus
then has to be unplugged (else a lot of ugly grafting of
leads onto the existing PSU wiring harness) . Thus, you
have to unplug the PSU from the mobo and put it's connector
onto another circuit board (or dongle style split) along
with the output from the battery pack to the motheboard and
other components needing power.

>Same molex serves the
>PC with power during the mini-ups's brief run. I dont know what the
>continuous current rating of those molexes is, but if the UPS only
>powers the system for 20 seconds its not going to be a problem.

6A, IIRC, but there's the voltage drop problem across the
connector and single supply leads making it too lossy.
You'll also have to switch the lead from input to output
around the charging circuit if I understand what you're
suggesting, then have the power going through these single
supply leads up to the PSU wiring harness distribution point
and down into the main PSU harness, which is quite a
distance to travel for the currents in a PC.




>> 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.
>
>You think so? I dont know, but I'd be mildly surprised if a large PC
>mfr didnt think there was any mileage in offering a mini built in UPS
>as an optional extra. Theres certainly a market for UPSes.

An OEM could come closer to the goal because they can limit
the unit's compatibility with certain systems' unique
current requirements. On the other hand we'd be cursing all
that much more about the proprietary way they ended up
getting the job done, OEMs don't need much of an excuse to
do screwy things that make it either impossible or very
costly to replace anything... keeping in mind that even if
the mini-UPS were to work there will always be a certain
failure rate and replacement requirement.