Unused Li-ion battery pack
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From: Jeff Liebermann on 4 Oct 2009 13:23 On Sun, 04 Oct 2009 11:27:07 -0400, Meat Plow <meat(a)petitmorte.net> wrote: >>Laptop monitor software to display battery temperature. >><http://www.passmark.com/products/batmon.htm> > >Interesting. 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. >>>>Rhetorical question: >>>>Why don't UPS manufacturers use Li-Ion batteries? 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. >>Still waiting for fuel cell laptop batteries. Polyfuel died in >>August. Ultracell is selling mostly to the military. >><http://www.ultracellpower.com/sp.php?rugged> >>Most of the major Japanese manufacturers have announced and even >>demonstrated products, but nothing I can buy, yet. Grumble... > >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. 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: <http://en.wikipedia.org/wiki/Car_battery#Terms_and_ratings> -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: Jeff Liebermann on 4 Oct 2009 13:46 On Sun, 04 Oct 2009 11:02:14 +0800, who where <noone(a)home.net> wrote: >Rhetorical question: Why don't UPS manufacturers use a decent >charging circuit in their SLA-backed UPS's? 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. <http://www.LearnByDestroying.com/pics/home/apc1400.jpg> 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: <http://groups.google.com/group/sci.electronics.repair/msg/e99a0f155fc198c0> <http://groups.google.com/group/sci.electronics.repair/browse_thread/thread/cf5ea1e3f3a01d4f/> -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: who where on 4 Oct 2009 22:17 On Sun, 04 Oct 2009 10:09:19 -0700, Jeff Liebermann <jeffl(a)cruzio.com> wrote: >On Sun, 04 Oct 2009 11:07:27 +0800, who where <noone(a)home.net> wrote: > >>On Sat, 03 Oct 2009 10:27:21 -0700, Jeff Liebermann <jeffl(a)cruzio.com> >>wrote: >> >>>Yep. Seen any Li-Ion battery chargers that have a settable EOC (end >>>of charge) adjustment? I haven't. >> >>Yes, the design I did allowed selection of 4v10 and 4v20 EOC. > >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. 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. >>(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). > >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. (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. >>>One could program it to stop >>>charging at perhaps 80% of charge, and somewhat extend the life of >>>batteries that are in 7x24x365 laptops. Also useful for the spare >>>batteries that I carry in the bag. Left fully charged, they also tend >>>to die early. >> >>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. > >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. (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.
From: Jeff Liebermann on 4 Oct 2009 22:35 On Sun, 04 Oct 2009 10:59:04 +0800, who where <noone(a)home.net> wrote: >The Windoze setting is purely for functionality - so the user can bail >before the pack pulls the plug and causes that "You didn't shut >Windoze down properly, so I'm doing a disc scan" screen on restart. That only happens with FAT and FAT32. NTFS has a journaling filesystem: <http://en.wikipedia.org/wiki/USN_Journal> 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. >The pack protection modules we used were preset to open the series FET >switch at 3v0. If you look at the discharge curve of Li-Ions at >constant current (or with a constant load impedance) you will notice a >distinct droop below about (from memory here) 3v3. While cell >deterioration starts at/below 2v5 there is very little useful capacity >gained by proceeding below 3v0. 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: <http://www.mpoweruk.com/performance.htm> 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. >>No problem. However, I'll stand on the Wikipedia 20%/year loss at >>100% charge at room temperature for commodity laptop batteries. My >>results were even worse. I'll concede that there are new chemistries >>that offer substantial improvements in self-discharge and >>self-deterioration, but I haven't seen any in laptops. > >Cost. Commodity chemistries have been around for over a decade and >are cheaper than newer solutions that aren't into the same part of the >volume/cost curve yet. 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. >Remember that the laptop manufacturer >generally sees the battery pack as a non-warranted item (wear and >tear), and even when it IS warranted it only has to function for that >period without any capacity guarantee. So cheap is good for them. 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. >>The user can set the Windoze low battery warning to trip at a much >>higher level than the ridiculously low default value of 10%. That >>will prevent excessive discharge. > >Yes (see earlier) but I was referring to end-of-charge setpoint. 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: <http://www.mpoweruk.com/soc.htm> -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: Jeff Liebermann on 4 Oct 2009 22:48
On Mon, 05 Oct 2009 10:17:21 +0800, who where <noone(a)home.net> wrote: >Ah, I didn't say external ;-) It was an on-board jumper selection, >so the user would need to crack the case. 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. >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. 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. >>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. > >(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. 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%. >>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. > >(snip) > >Estimating SOC is a *lot* easier, trivial linear calculation. 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. >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. 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(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |