Unused Li-ion battery pack
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From: Jeff Liebermann on 3 Oct 2009 13:27 On Sat, 03 Oct 2009 10:25:53 -0400, Meat Plow <meat(a)petitmorte.net> wrote: >"room and above temperature" The battery pack is on the front ledge it >does not get hot from the laptop but gets "above" room temperature. >Just how much "above room temperature" I don't know never measured it >but it's surly not warm to the touch as the rear end is where the fans >and heat sink are located. Laptop monitor software to display battery temperature. <http://www.passmark.com/products/batmon.htm> It would be interesting if the protection circuit in the battery pack also logged temperature. That would be sufficient to estimate battery life and alert the user that the battery is too hot. >I've seen many including HP batteries go belly up in a short time. Yep. Seen any Li-Ion battery chargers that have a settable EOC (end of charge) adjustment? I haven't. 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. >>Rhetorical question: >>Why don't UPS manufacturers use Li-Ion batteries? Aw, you're no fun... 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... -- 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 3 Oct 2009 22:59 On Sat, 03 Oct 2009 00:10:54 -0700, Jeff Liebermann <jeffl(a)cruzio.com> wrote: >On Fri, 02 Oct 2009 14:03:46 +0800, who where <noone(a)home.net> wrote: (snip) >>If it is a laptop pack recent enough to care about, it will contain a >>pack protection module which will preclude discharge beyond a LVCO >>point, typically 3.0v, and will also preclude excessive discharge >>current. Nothing unsafe about a DYI discharge on that pack. > >True. The battery pack has enough electronics inside to protect >itself from excessive discharge. Under Windoze, one can set an alarm >and a shutdown point based on battery capacity. The default threshold >is about 10%. I've never tested this to determine if it works. >Presumably, if you don't want to run the battery down to below perhaps >25% capacity, setting a shutdown threshold below this point is wasted >effort. Similarly, if there's a protection threshold inside the >battery pack, it's certainly not labeled or easily determined. 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. 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. >>If it is a single cell from a cellphone or similar, different story. >>these tend to have minimal inbuilt protection (if any) and rely >>heavily on the host device for the customary protective functions. > >Yep. Model airplanes and helicopters are even worse. All the >protection electronics is in the external battery charger. It >protects against fatal overcharge, but does nothing for excessive >discharge. > >>No protection means all bets are off. > >Yep. > >>No need. I've seen numbers on these before, and Evgenij Barsukov has >>posted comment on this previously in sci.chem.electrochem.battery. > >(...) > >>I never suggested that everything you posted is wrong, far from it. >>But several points were amiss and they attracted specific comment. > >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. 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. >>I have seen numerous manufacturer-derived articles recommending 50-60% >>SOC and cool/cold but not freezing as the optimum storage condition >>for maximised life. > >Same here. That's also my recommended storage condition. > >>I see nothing at all wrong with this approach >>*if* maximum life is the sole objective. If OTOH the user wants to be >>able to pull the cell/battery out of storage and into service without >>an intervening warm-up or recharge, maybe a higher SOC is warranted. >>Like many things relating to Li-XX cells, it is a tradeoff. > >Well, of course. I mentioned (twice) that one should let the battery >warm to room temperature before using. I don't know what will happen >if the battery is either charged or discharge at near freezing >temperatures, but it probably will not do anything useful. > >>The extra life obtained by reducing the EOC voltage is well documented >>and well worth it in laptop applications BUT the end user doesn't get >>to choose. The manufacturer is out to deliver (well, promise) the >>maximum discharge runtime he can, and he doesn't give a rats how long >>the pack lasts in service. > >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. >>I have a pack from an olde Acernote Lite 370 series dated 9637, so it >>is just over 13 years old. It is stored with, but not *in*, the >>machine. About once every year or so I pull that out and run it until >>the machine shuts down, then recharge it to 100% (sic). It delivers >>about 1.3 hours, compared to 2.5+ when new. That is stored at 100% >>and room temperature (32S/116E). > >The Acernote Light 370 was delivered with NiMH batteries, but later >LiIon batteries were made available. Yep, I have both here (two 370's) and the NiMH is thoroughly rooted. >Why do you discharge the battery before charging? As I understand it, >LiIon doesn't have a memory problem. It doesn't, but the only way I can sensibly evaluate it's usable capacity is by measuring runtime. >>I also have several test packs of 18650 cells left over from a project >>about five years ago when I designed a commercial Li-XX charger. They >>were shelved at 4.20v and currently all are above 3.9v. I haven't >>bothered to measure their storage capacity because I have no reason, >>but I can assure you that they wouldn't show that sort of cell voltage >>if they had lost 20% of original capacity per year. > >Agreed. 3.92v is the highest voltage that a LiIon-Cobalt cells will >deliver. You did something right because my 6 month experiment showed >deterioration in both room temperature batteries. These are cheap (Chinese) 18650 commodity cells which my client imports. Far from special. To evaluate the prototype charger I set the EOC to 4v20 and did cyclical testing on packs of 1/2/3/4 cells. There were some interesting points to emerge from this, but somewhat O/T for this thread.
From: who where on 3 Oct 2009 23:02 On Sat, 03 Oct 2009 06:35:31 -0700, Jeff Liebermann <jeffl(a)cruzio.com> wrote: >Rhetorical question: >Why don't UPS manufacturers use Li-Ion batteries? 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?
From: who where on 3 Oct 2009 23:07 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. (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). >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.
From: Geoffrey S. Mendelson on 4 Oct 2009 02:24
who where wrote: > 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(a)mendelson.com N3OWJ/4X1GM |