Post by thread:[EE]: Lithium Ion Battery Packs

Li-ion has this really neat runaway failure mode which can make them catch fire or explode. Thus they are very careful about their treatment and no one will sell packs without that circuit. The circuit will disconnect from the battery if it is overcharged. It will also disconnect if overly discharged; this also protects the battery. Despite all this if you charge a discharged pack or put a load on the overcharged pack the battery should reconnect. I played with one of these myself on a lab power supply. Of course yours might really be broken in which case I don't know. But check the circuitry for a fuse. Barry {Quote hidden}>Does anyone know why lithium ion battery packs fail so easily? I've had >two die on me in under a month, two separate types of devices too. I've >been told that it's not the cells, but the little circuit in the pack >that dies, which renders the pack useless. Anyone have any idea why this >happens, what causes it, and why they aren't a bit more robust? Also a >general question, should I be keeping the battery packs charged when not >in use (i.e. does allowing them to self discharge over a period of >months adversely effect their life)? > >Thanks for any help, > >Josh >.....joshyKILLspam@spam@mb.sympatico.ca -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Lithium Ion battery packs are not for the faint of heart. Sony and Apple lost facilities to fires caused by Li-ion failures, and the company I used to work for had several small fires, contained by elaborate engineering controls. The protection circuit usually consists of a voltage comparator chip and one or two FETs used to interrupt the battery current during overcharge and underdischarge conditions. The voltage comparator senses each cell in the battery stack separately. You have to disconnect the cells and charge/discharge the cell that is out of balance before you can reconnect the circuit. Permanently disconnecting the circuit is asking for trouble. Barry Gershenfeld wrote: {Quote hidden}> Li-ion has this really neat runaway failure mode which can make > them catch fire or explode. Thus they are very careful about > their treatment and no one will sell packs without that circuit. > > The circuit will disconnect from the battery if it is overcharged. It > will also disconnect if overly discharged; this also protects > the battery. Despite all this if you charge a discharged pack or > put a load on the overcharged pack the battery should reconnect. > I played with one of these myself on a lab power supply. > > Of course yours might really be broken in which case I don't > know. But check the circuitry for a fuse. > > Barry > > >Does anyone know why lithium ion battery packs fail so easily? I've had > >two die on me in under a month, two separate types of devices too. I've > >been told that it's not the cells, but the little circuit in the pack > >that dies, which renders the pack useless. Anyone have any idea why this > >happens, what causes it, and why they aren't a bit more robust? Also a > >general question, should I be keeping the battery packs charged when not > >in use (i.e. does allowing them to self discharge over a period of > >months adversely effect their life)? > > > >Thanks for any help, > > > >Josh > >joshyKILLspammb.sympatico.ca > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 09:26 PM 5/7/01 -0400, Alan Beeber wrote: >Lithium Ion battery packs are not for the faint of heart. Sony and Apple lost >facilities to fires caused by Li-ion failures, and the company I used to work >for had several small fires, contained by elaborate engineering controls. Reminds me of my "battery box" for experimental circuits. 3/8 lexan "coffin" 10 x 4 x 4 inches inside, with something like 10 or 12 screws holding down the lid. Sides had 1/4 inch vents, with an outer vertical wall so that NOTHING could fly out of the box without hitting a wall, but there wouldn't be enough overpressure to pop the lid. I never needed it, but I often used it :) Don't know where it finally ended up. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Lithium Ion Battery packs are extremely sensitive. You can't buy lithium ion batteries bare from the major manufacturers. If you are using the pack in a way that makes the circuit break, you are using it incorrectly and should be glad the protection is there. These things WILL explode violently, unexpectedly, and will always land butter-side down. It sounds like you don't know much about lithium ion rechargeable batteries (otherwise you wouldn't be asking us about the protection circuit). You cannot charge them the same way you charge NiMH, never mind NiCd. You'd best leave the job to a dedicated Li-Ion battery charging IC such as those available from linear technology. You'd probably be better off getting a charger from the firm that sold you the packs and integrating that into your product/project until you have a very good understanding of how to deal with Li-Ion. As far as your question, trickle charging is NOT recommended for these packs, their self discharge rate is quite low compared to NiMH or NiCd, and allowing them to self discharge will not affect them adversely. Keep in mind that they can only be recharged (reliably) 300-500 times as compared to NiMH's 400-600 and NiCd's 800-1200 times. They are getting better. While trickle charging itself does not damage the cell when done right, it is unnecessary when the cells are charged and used correctly. A proper recharging circuit will charge the cells only when needed, and not at any other time. Oh, and please keep in mind that there are currently two major chemistries for Li-Ion batteries, and the charging for the two chemistries is different enough to cause problems if you try and charge one like you'd charge the other. Finicky, finicky, finicky little creatures. If you can manage with NiMH I'd recommend it for now. Besides, all the Li-Ion production is being sucked up by cell phone and laptop industries, so your production lines are going to be idling a lot unless you have some amount of clout in the industry (or deep pockets). -Adam (returning from the dead when he figures out how to import Eudora mail into netscape...) At 05:24 PM 5/7/2001 -0500, you wrote: {Quote hidden}>Does anyone know why lithium ion battery packs fail so easily? I've had >two die on me in under a month, two separate types of devices too. I've >been told that it's not the cells, but the little circuit in the pack >that dies, which renders the pack useless. Anyone have any idea why this >happens, what causes it, and why they aren't a bit more robust? Also a >general question, should I be keeping the battery packs charged when not >in use (i.e. does allowing them to self discharge over a period of >months adversely effect their life)? > >Thanks for any help, > >Josh >.....joshyKILLspam.....mb.sympatico.ca > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hi Adam, thanks for the reply. Perhaps I misrepresented myself in asking the questions that I asked. I in fact know nothing about LiIon batteries. I don't intend on using them in any product or anything. However, they are used in two devices I own, a Sony MZR30 Minidisc recorder, and a Yaesu VX-1R ham radio. Both battery packs died within a few weeks. Rather, I left both devices idle for awhile, then when I went to charge them, on two unrelated matters, but within a few weeks of each other, both devices refused to charge their pack. I was (am) quite annoyed because of how much it will cost me to replace the packs, and I was wondering why they fail, and how to keep them from failing. As far as I can tell, the only bad thing I have subjected this packs to is my inattention. Any ideas? Thanks, Josh EraseMEjoshyspam_OUTTakeThisOuTmb.sympatico.ca "M. Adam Davis" wrote: {Quote hidden}> > Lithium Ion Battery packs are extremely sensitive. You can't buy lithium > ion batteries bare from the major manufacturers. If you are using the pack > in a way that makes the circuit break, you are using it incorrectly and > should be glad the protection is there. These things WILL explode > violently, unexpectedly, and will always land butter-side down. > > It sounds like you don't know much about lithium ion rechargeable batteries > (otherwise you wouldn't be asking us about the protection circuit). You > cannot charge them the same way you charge NiMH, never mind NiCd. You'd > best leave the job to a dedicated Li-Ion battery charging IC such as those > available from linear technology. You'd probably be better off getting a > charger from the firm that sold you the packs and integrating that into > your product/project until you have a very good understanding of how to > deal with Li-Ion. > > As far as your question, trickle charging is NOT recommended for these > packs, their self discharge rate is quite low compared to NiMH or NiCd, and > allowing them to self discharge will not affect them adversely. Keep in > mind that they can only be recharged (reliably) 300-500 times as compared > to NiMH's 400-600 and NiCd's 800-1200 times. They are getting > better. While trickle charging itself does not damage the cell when done > right, it is unnecessary when the cells are charged and used correctly. A > proper recharging circuit will charge the cells only when needed, and not > at any other time. > > Oh, and please keep in mind that there are currently two major chemistries > for Li-Ion batteries, and the charging for the two chemistries is different > enough to cause problems if you try and charge one like you'd charge the other. > > Finicky, finicky, finicky little creatures. If you can manage with NiMH > I'd recommend it for now. Besides, all the Li-Ion production is being > sucked up by cell phone and laptop industries, so your production lines are > going to be idling a lot unless you have some amount of clout in the > industry (or deep pockets). > > -Adam > (returning from the dead when he figures out how to import Eudora mail into > netscape...) > > At 05:24 PM 5/7/2001 -0500, you wrote: > >Does anyone know why lithium ion battery packs fail so easily? I've had > >two die on me in under a month, two separate types of devices too. I've > >been told that it's not the cells, but the little circuit in the pack > >that dies, which renders the pack useless. Anyone have any idea why this > >happens, what causes it, and why they aren't a bit more robust? Also a > >general question, should I be keeping the battery packs charged when not > >in use (i.e. does allowing them to self discharge over a period of > >months adversely effect their life)? > > > >Thanks for any help, > > > >Josh > >joshyspam_OUTmb.sympatico.ca > > > >-- > >http://www.piclist.com hint: PICList Posts must start with ONE topic: > >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

How safe is this disconnect/discharge/recharge/reconnect operation? I'd rather spend the money than risk well...me. Also, I haven't opened this packs up, but what if there is only one cell? Is it possible for the cell to simply die? Thanks, Josh @spam@joshyKILLspammb.sympatico.ca Alan Beeber wrote: {Quote hidden}> > Lithium Ion battery packs are not for the faint of heart. Sony and Apple lost > facilities to fires caused by Li-ion failures, and the company I used to work > for had several small fires, contained by elaborate engineering controls. > > The protection circuit usually consists of a voltage comparator chip and one > or two FETs used to interrupt the battery current during overcharge and > underdischarge conditions. The voltage comparator senses each cell in the > battery stack separately. You have to disconnect the cells and > charge/discharge the cell that is out of balance before you can reconnect the > circuit. Permanently disconnecting the circuit is asking for trouble. > > Barry Gershenfeld wrote: > > > Li-ion has this really neat runaway failure mode which can make > > them catch fire or explode. Thus they are very careful about > > their treatment and no one will sell packs without that circuit. > > > > The circuit will disconnect from the battery if it is overcharged. It > > will also disconnect if overly discharged; this also protects > > the battery. Despite all this if you charge a discharged pack or > > put a load on the overcharged pack the battery should reconnect. > > I played with one of these myself on a lab power supply. > > > > Of course yours might really be broken in which case I don't > > know. But check the circuitry for a fuse. > > > > Barry > > > > >Does anyone know why lithium ion battery packs fail so easily? I've had > > >two die on me in under a month, two separate types of devices too. I've > > >been told that it's not the cells, but the little circuit in the pack > > >that dies, which renders the pack useless. Anyone have any idea why this > > >happens, what causes it, and why they aren't a bit more robust? Also a > > >general question, should I be keeping the battery packs charged when not > > >in use (i.e. does allowing them to self discharge over a period of > > >months adversely effect their life)? > > > > > >Thanks for any help, > > > > > >Josh > > >KILLspamjoshyKILLspammb.sympatico.ca > > > > -- > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

While I'm certainly not an expert in Li-Ion batteries, I've read by share of data sheets and have concluded that a lot of the paranoia is 1) overstated, and 2) comes into play mainly when you're aiming at maximum charge, maximum lifetime, and minimum charge time. I've been taking apart discarded battery packs to individual cells for quite some time now. Usually most of the cells still have 4+ V on them and will make a credible attempt at melting your tools if you're careless and short them out. The additional electronics varies a great deal in complexity, and I haven't analyzed any of them for failure analysis. I charge (occasionally - I should stress that I haven't done this for more than a dozen or so cells) the cells individually using a lab-style CCCV power supply set to 4.1V and 0.5A or so (this is very close to the idea charging method, assuming that my voltages is accurate to 1% or so.) I've yet to see sign of overheating or other stress (well, except for that cell I connected backward for a couple hours.) If my cells are 4.2V chemistry, well, then I'd be consistantly undercharging them a bit, so I wouldn't get full capacity out of them and I might affect their overall lifetime. [Since these are "free" cells, I don't much care on those points.] I HAVE discovered that you can apparently make a Li-ion cell VERY dead by over-discharging it. If I turn off the CCCV power supply, it leaves a low-impedence meter across the outputs. Leave a cell on there for 24 hours or so before you notice, and it will have discharged to 0V and will NOT allow itself to be recharged again. I did have a conversation once with someone who had worked at a LiION manufacturer, and they admitted under some pressure that some of the more spectactular results that had been mentioned occured when a cell was punctured, shorted, AND overheater (ie external fire.) This is "modern" cells, of course. I'm also given to understand that older cells were more exciting... BillW -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics