Not-so-rhetorical answer: Cost. SLA's are cheaper commodities and also require less attention (cost) to safety aspects. Weight and kJ/kg don't matter in a UPS.
Rhetorical question: Why don't UPS manufacturers use a decent charging circuit in their SLA-backed UPS's?
Yes, the design I did allowed selection of 4v10 and 4v20 EOC.
(Technically it isn't the EOC point, rather the transition from CC to CV charging. True end-of-charge is generally triggered when the charge current at constant voltage tapers off to a predetermined figure like 10% of the CC rate. But it does set the final charged state and voltage).
That was one reason for the selection to be available. Unfortunately (as I mentioned earlier) laptop manufacturers have one objective - maximum runtime for minimum cost.
And weight. If cost and reliability were more important, they would use nickle metal hydride cells. The cells are almost indestructable, easy to charge, have no reputation of early failure or catching fire, and so on. They can be reconditioned by draining them completely, which they actually seem to do well with unlike any of the lithium cells.
Somewhere along the way, people decided that expensive lithium cells were "in" and nickle metal hydride cells were for flashlights and $10 MP3 players.
This is IMHO one of the great failings of portable device design in this century. What surprises me is that no one has picked up on this in the "climate change" crowd, lithium cells use rarer materials and are much more dangerous to the environment if dumped in the trash, which is where most of them end up. (or worse, a recylce heap in China.)
Geoff.
-- Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
What are the differences between decent and indecent charging circuits?
and invariably a much higher self-discharge rate, although more recently this has improved a lot (although *after* Li-Ion gained widespread acceptance).
Weight and volumetric superiority were the main attractions, particularly for cellphones. You could fit about twenty of my Nokia GSM phone's pack inside the NiXX pack for my old Motorola analog flip.
which is the *same* as dumped in the trash :-(
Don't get me started on CFL's ...
Quite simple really.
Decent ones recharge the SLA's with a sensible regime that supports longevity while providing a reasonable recovery after disharge.
Indecent ones overcharge the SLA's and fsck them.
That's not really fair. My Motorola flip used 6 volts, and needed about 1 amp to transmit while you were speaking. It used the AMPS system which was basicly FM radio.
It also needed 50ma on standby.
My current cellphone (a really cheap Alcatel GSM) has a 450ma 3.6 volt battery.
In Nimh terms that would be 3 cells each 1/2 AAA size. Not much bigger or heavier, if at all then the lithium battery in it. It would also be ok to run it down to zero, and with the new cells last a year without discharging (or about a week in the phone, even with it off), and go through 1,000 cycles before dying.
As for relative size, you could put 5 or 6 of the Alcatel phones in the
1600mah pack for the flip. I actually had a lithium battery for it, it was the size of the 600mah nicad, but held 1000mah. Cost around $100.Geoff.
-- Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
Interesting.
The charge circuit in the Asus obviously has done a great job with this battery. Although now used 3 times a week for a couple hours a day however it remains on ac power 24/7.
Well it was a rhetorical question.
I have a lead acid jumpstart pack boasting a 900 amp (heh) surge and a
200 watt inverter. Never used it in that configuration but I would assume several hours of usage would not be out of reason.
User selectable? That sure would be nice. If so, that's the first charger I've seen that offers any manner of early EOC control by the user. Sometimes, it's internally selectable by a jumper, pot, or component selection. However, I've never seen it user accessible much less properly documented.
I think (not sure) that simply disabling the CV part of the charge cycle would be sufficient to stop charging at about 80% of full charge.
Yep. The math for calculating how far down a Li-Ion battery pack is discharged is fairly simple if I make a number of assumptions. Load can be estimated by removing the battery, and running the laptop solely on the charger. Measure the charger current while using as much power as possible (full LCD backlight, run a DVD movie, no CPU slowdown). It's usually fairly close to the current rating of the charger. If you're lazy (like me), just use the charger current spec.
Estimating the average load and duty cycle is not easy. I use 10% of maximum, which is probably wrong for many applications and users, but is a fair starting point. I'm also ignoring charger efficiency which I assume is fairly high.
Using a handy IBM Thinkpad R40 as an example, the charger is rated at: 16v 4.5A. 16v * 4.5A = 72 watts. Using my 20% duty cycle guess, we have an average load of 14.4 watts.
The battery is rated at 14.4v 4000ma-hrs or: 14.4 * 4A-Hr = 57.6 watt-hrs.
So, if we fully charge the battery, and run it to depletion, we can theoretically have: 57.6 watt-hrs / 14.4 watts = 4 hrs. My R40 typically will run about 2 hrs which is down to perhaps 50% of full charge. I should probably do the same calculation with one of the new Netbook computers, which is more sensitive to battery selection but are also conveniently rated in hours of operating time.
Most of the vendors use MobileMark 2007 ($400) software for determining their battery run time under a controlled work load:
See
Section 2.5 and 4.4 have battery run time criteria which is rated down to 7% of battery capacity. Little wonder they get inflated run time numbers.
Note: Run time = how long the laptop or battery will run. Life time = how long the battery will last before replacement.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
The point is that it is possible to monitor the operating temperature of the battery and then offer suggestions on how to prolong the battery life based on the measurements. It's also possible to predict imminent battery failure with this information. However, in our consumption based society, such things are rarely supplied.
UPS's spend much of their life with fully charged batteries. They also tend to run rather warm inside. This combination is not compatible with Li-Ion batteries, which die prematurely when run hot and fully charged. If run like a typical UPS (which is almost never run), it would make a great battery killer. The reduction in weight and hazardous substances might be beneficial for some applications, but there's little demand for lightweight or non-toxic backup power. One might do better using capacitors instead of a battery.
Huh? I was pitching fuel cell (methanol) power systems, not lead acid. Read what I wroth. Pour your booze into the fuel cell and get enough power to run your computah for a few hours.
Also, it's not "surge". It's probably "xxxxx cranking amps" or some such contrived measurment designed to avoid specifying standardized amp-hr battery capacity. Pick one:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Many years ago, I accused APC of intentionally setting the charger in some models to prematurely destroy batteries and create hazardous conditions (bulging, leaky, and overheating batteries). Specifically, the early APC 1400RH 4ru model was the major culprit.
It has 4ea 12V 7A gel cells in a series-parallel derangement. We had about 35 of these installed at various installations, all of which rapidly ate batteries. Eventually, these UPS's were removed when it was found that the batteries had bulged and leaked so much that extraction was impossible. I ended up with most of them and tried redesign the charging circuit. APC was totally uncooperative. I don't want to go into the details, but eventually APC released a totally new 1400RH model, with a slightly improved charging circuit.
During this adventure in frustration, I learned a few things about UPS charging philosophy. The customers want the batteries to recover as fast as possible after being run for a while. That's because power outages tend to come in clusters, like during a storm. Fast recharge is an important requirement. Given the choice of long battery life and fast recharge, most customers will choose fast recharge. More to the extreme, when faced with the possibility of killing the battery just to get it charged quickly, most customers will accept the cost of a new battery pack rather than risk any additional server downtime.
So, rather than a modern staged charging system, that tapers off near the EOC, and is intentionally easy on the battery, the typical UPS battery charger is designed to get as close to 100% of charge as quickly as possible and never mind going into overcharge. That results in dramatic changes in EOC threshold with aging batteries, connector losses, manufacturing variations, etc. Basically, you can have long battery life, or fast recharge, but not both.
My current guess(tm) is that UPS charging circuits are designed first for fast charge and secondarily for maintaining as close to 100% charge as possible. Both of these are detrimental to long battery life, so the charging is selected for a "reasonable" battery life of about 3 years (depending on model).
Some of my previous rants on the subject:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Ah, I didn't say external ;-) It was an on-board jumper selection, so the user would need to crack the case. This charger was for "commercial/industrial" users and supplied as a companion device to their custom 1/2/3/4-cell packs. T'was documented for the vendor so he could set it to best suit the end-user application.
(Checks project report ...) On my 18650 testing, transition occurred at ~59% when charging at 0.55C. Asthere is obviously a finite ohmic impedance characteristic, transition would occur later at lower rates.
(snip)
Estimating SOC is a *lot* easier, trivial linear calculation. From fully charged (and preferably "rested"), discharge until the PACK shuts off the pooter. Observe run time. Deicde what % you want left in your pack, repeat above and terminate when that proportion of the full runtime remains.
That only happens with FAT and FAT32. NTFS has a journaling filesystem:
which does not require a fsck if the user or battery protection circuit suddenly pulls the plug.
Incidentally, no kudos to Western Dismal for selling their Passport series of USB drives with FAT32, thus insuring that pulling the plug will trash some recently written data. I reformat or use Windoze "convert.exe" all of these to switch to NTFS.
Well yes.... any storage device, with a low internal series resistance will exhibit a fairly flat discharge curve followed by an abrupt droop. See the first graph at:
The problem is that the sharp knee is somewhere between 5% and as little as 1% of capacity. To prevent running the battery into the ground (and possibly reverse polarizing some of the cells when connected in series), the dropout point is as close to the beginning of the droop as possible. That's fine for a new battery, but as the battery ages, the same threshold slowly moves up the charge curve as the terminal voltage decreases. I don't think any of the SOC chip vendors compensate for this.
Agreed. It does take time for new technology to decrease in price. However, there little incrimental benefits to switching to a superior chemistry or technology. For a few percentage points increase in performance, the exponential increase in cost makes it a bad investment. Mediocrity tends to be permanent until a new mass market can be found, or until some external influence (environment, scarcity of materials, hazards, safety, etc) demands a replacement. Methinks we'll be seeing the commodity Li-Ion battery, with its 20% capacity loss per year, for quite some time.
Generally true but there are exceptions. The Sony manufactured batteries full of metal shavings that would catch fire with little provocation was covered under various warranties. I had 4 laptop batteries (out of maybe 200) replaced under this warranty. However, for general use, you're correct. There is no battery warranty. About
10 years ago, I received 4ea Compaq Presario 1620 series laptops, each with a spare battery. Most of the batteries died within 5 months including the ones that were left in the original packaging and not used until tested. Compaq (pre-HP) declared this to be "normal battery life" and refused to do anything. 3rd party Li-Ion battery packs were somewhat better and lasted about a year. We switch to the older NiMH batteries, which were half the price, and lasted 3 years. Your horror stories may vary.Ok, got it. Still, the Windoze low battery warning feature is quite useful. I have mine set to warn me at 40% and shut down at 25%. Too soon to tell if this will extend the life of the battery pack.
Incidentally, some interesting reading on SOC (state-o-charge) technology:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I suspect there's a bit of assumption in there. Most consumers of "small/desktop/soho" UPS don't have the slightest clue how they work or what goes on with them. The manufacturer makes assumptions on the buyer's behalf, but obviously slanted towards the manufacturer's ends. I have found UPS owners who maintain that they had to have failed units refurbed by the mnaufacturer.
You can achieve a *reasonable* compromise if a bit of effort is spent on charger design. SLA's are best fed with a current-limited constant voltage regime. Bulk charge recovery is achieved under the CL phase, and setting the limit high to achieve fast replenishment isn't of itself a battery-killer. BUT once the reasonable SOC has been achieved and even before transition occurs, the CV fgure should be reduced. And float voltage should similarly be reduced in recognition that the average UPS spends say an hour a year (max) on discharge. They don't need to be kept at 100%. They *should* be kept at a sustainable (aka survivable) float condition, and if that loses capacity the user needs then the user should have bought a better sized unit.
None of this is news to you of course.
As an aside, I have equipped a several torches here with 6V 4Ah SLA's in place of the original dry cell (4F?) pack (and changed to a 6V krypton lamp). These are recharged as required using the Unitrode/TI UC3906, to whose charge regime I continually refer people when they enquire about care and feeding of SLA's. The current batch of SLA's are over 10 years old.
Yep.
IMOE there you are being kind to the UPS makers.
I've also experienced the drama of extracting dried/cracked/swollen SLA's from their enclosures. Just like laptop manufacturers, UPS makers are guilty of self-serving design without regard for the downstream cost to the end user.
Grumble. That's what I want on my chargers. Actually, what I want is complete control over just about every parameter involved in charging, but would create its own collection of problems. The market for such things is probably fairly small.
I'll bet that the vendor does NOT supply this information to the customer. Like I previously mumbled, I haven't seen any Li-Ion chargers that give the customer any EOC control.
Ok, bad guess on my part. Maybe estimating the time needed for a CV charge to get to 100%, and cut it in half to get 80%.
I wasn't looking for the SOC. That can be done by counting coulombs (amps and seconds). What I was calculating was the run time of the computer until the battery pack gives up. That's the mysterious specification offered my many laptop vendors that reeks of science fiction and cooked data. The number of variables involved in an exact calculation is sufficiently high that most vendors will simply use an empirical number, rounded up to the nearest integer.
No problem except you don't specify what the computer is doing while discharging the battery. There's a huge difference between sitting at standby keeping the dynamic RAM alive, and beating up the CPU with compressed video, spinning DVD drive, and full brightness backlighting. It's as bad as the spec for the number of pages a laser printer toner cartridge will deliver.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Indeed. You'd want one (or two), I'd keep a couple, a few more into the s.e.d types, and probably a dozen for the rest_of_world.
It was a jumper on pin headers, extending it to the front panel would be a snap.
The controller I used was the MAX1737. You get a certain amount of flexibility designing around it, and we (the client and I) preferred their regime to the others we considered.
The selection was vendor-made based on the end user's stated role, and was selected in_conjunction_with pack sizing. Any time the role looked like prolonged high SOC and temperatures above 30C, he'd go with 4v10 and the pack size would then be determined. He didn't want premature failures, unlike laptop makers who don't give a rats.
It's linear - CC - in CL mode.
Maybe I missed your objective. I understood it to be determining when to stop discharge (in the laptop) to achieve a chosen SOC. Any time you are playing with discharge the laptop activity is fundamental, but for a known target SOC it isn't hard to invoke a known task (eg screen saver) and do the linear maths.
It wasn't a sharp drop that we saw. More of a curve than a cliff.
I'm not aware of any that do. But with the (IIRC) Mitsumi chips we used, there was less need than with say nickel chemistries. The module monitored cell voltage differences, and would prevent operation if the differences exceeded a preset threshold value. With EOD set at
3v0 (average cell), there is no way any cell would get near to 2v5.just like the corner of the engine bay on automobiles still features lead-acid ....
That's an identified manufacturing fault, totally different from a wear-and-tear situation.
I was thinking more of something with a built in ethernet or USB port. All the charge parameters can be setup on a web page. Once one has a suitable processor, adding features such as battery history, battery test, counterfeit detection, run time calculation, and fire detection are mostly software. I'm half way inspired to design and build one for myself but suspect that I can't make much money on it at consumer price levels.
Ok, but that's pure analog. Analog is not a problem but it does limit what weird things can be done with a Li-Ion charger. I was thinking more in the way of a digital (i.e. PIC controller) design, such as:
and increasing the output current capabilities to run larger battery packs. For example, when the battery pack is in the charger and allegedly fully charged, it would be fairly easy to apply a load and discharge it for perhaps a minute or more. The asymptote of the terminal voltage curve can be extrapolated to produce an estimated runtime. Some of the remote battery management systems already do this quite accurately. One could also include some RAM and add a data logger and coulomb counter (amp-seconds). The area under the current curve is the charging and discharging energy. This would give a good clue as the battery packs comparative quality (something that I suspect the manufacturers would not be interested in supplying).
Good plan. However, there's always going to be the customer that plugs in a new battery pack, runs it as long as possible, and then proclaims that they're not getting the specified run time.
It was to see how close to a full charge was being used and where the battery droop detection was set. That's measured in coulombs (watt-seconds) or run time (hours). I have a Kill-a-Watt meter that measures power consumption from the 117VAC line. I run the laptop only from the charger, with the battery removed, for about 30 minutes (the limit of my attention span), doing what I consider to a typical applications mix. The Kill-a-Watt meter records the watt-seconds (actually watt-hrs) used. It also compensates for power factor. I throw in the switcher efficiency of about 85-90%:
and calculate the energy consumption per hour of use. I use that as the average load for run time calculations.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Sorry. I shouldn't have said "abrupt". It does tend to dribble off with a rather soft knee. Also, if you have several mixed cells in series, of different ages, the knee will appear at different points in the discharge curve for each cell. The knee will also be less defined. (A good reason not to mix different age cells).
AN AGING MODEL FOR LITHIUM-ION CELLS
Warning: 278 page of a grad student's dissertation. Skipping to Chapter VI - Conclusions, where it says: A direct correlation was found between the cell capacity and the open-circuit voltage of a fully discharged cell. Cell resistance increased at a linear rate throughout the life of the cells.
The circuit doesn't monitor individual cells. I would think that one cell with a bad case of premature aging might cause problems. I'm beginning to think that I'm worrying over a non-problem. Never mind.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
The brief was "KISS". The end-users were real industrial users, and quite disinclined to fiddle of even treat the pack and charger as other than a black box.
If they weren't getting the specified run time, it would be the result of improper sizing (vendor fault or user-supplied misinformation), or faulty pack or charger (vendor responsibility). Easily resolved.
Recall that the pack size was chosen AFTER the CV limit was determined.
The problem with those meters is that - being cheap/chinese - they tend to poorly handle the line current "blips" into a rectifier. And even if they returned true RMS, that doesn't itself reflect the actual power drawn in those circuits.
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