kony wrote:
> 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.

Neither of us really knows what size cells, but of course theyll be
sized for the job. However given that D cells can knock out 60A
there doesnt seem much doubt that it'll all fit in a standard 5.25"
case.

I'd look at NiFe rather than NiCd though. With their very high
current ability they can be made smaller and more V stable.


> >> >> 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.

those other parts are fairly small volume-wise.


> >> 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?

I'm not planning any extra wiring required inside the PC. Why do you
think there would need to be? V_drop too high?

Why would a business user choose an inbuilt miniups?
1. Because they dont want to fork out on a large whole site UPS, nor
have loads of mains plugin UPSes cluttering up the place.
2. Lower cost than an external plugin UPS
3. Ease: just tick the box on the form and you get a data-safe PC.
4. Any company PCs used offsite will always be UPS protected
this way


> 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.

main psu doesnt go through the batt pack, the wiring in the pc is
not affected, the miniups just plugs into a molex connector, end of
job. If running the Pc's original wiring loom proves too high a
V_drop
to set the batt pack out a little higher and run it open loop, then
there would also need to be an exrta sense wire tagged on. Very
easy.


> >> 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.

You're way overcomplicating this. The battery pack output stays
connected via a relay whenever the machine is on. At power down
it senses that and continues supplying power for 15s (ie it doesnt
distinguish mains failure from normal power down) then cuts out.

A possible way to control charging is to connect the half way point
on the batt pack to each rail (0v or 12v) via a basic reg, thus
charging each half of the pack alternately. Doide & R ensures the
pack and its halves can discharge very fast but only charge at a
trickle.


> >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.

Do you know what the R or range of R is? I've not measured it. The
ATX Vspec allows a fair amount of swing IIRC

> You'll also have to switch the lead from input to output
> around the charging circuit if I understand what you're
> suggesting,

trying to avoid any such switching if poss. If we switched the batt
pack between charge and out, a power failure would mess with the
pc before the relay clicked in.


> 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.

yeah. If too much R and load variation we could resort to an extra
sense wire to fix it. That would require a high current reg though,
best avoided if poss.


> >> 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.

They do things proprietary ways mainly because they can save
money. 20p off 10,000 units is £200, os if they can do it non
standardly for a few p less they will. But I dont see proprietary vs
not having a big effect on viability. One PC mfr would only capture
part of the market, but people buying new systems are an attractive
target for addons, especially if they promise to safeguard against
business data corruption or loss, and do it at lower cost than
anyone else's UPS, and with less hassle..


NT