OhPardonMe Posted April 25, 2016 Share Posted April 25, 2016 I have a generic unicycle with a generic 130Wh battery (16 2200mAh cells in series). Over time, the battery life has degraded significantly to the point where if I charge it now, no more that 3 of the 4 LED's will turn on when the battery is fully charged, and I can't get more than 1km of distance out of it. Someone correct me if you think it may be something else, but I believe that 3-4 of these cells have died which brings the fully charged voltage of the overall battery down to ~50 Volts (I haven't gotten access to a multimeter to confirm this), and the BMS will cut it off even though the 12-13 good cells still have most of their charge left. My questions are the following: 1. Does the charger/BMS know when there are bad cells and account for this so that the remaining cells aren't overcharged or damaged? 2. Is there a way to jumpstart the individual "dead" cells while they're still in series with the others? 3. Is it safe to remove and replace the dead cells with new ones/ Does anyone know if the cells are typically soldered in or attached in a semi-permanent way on these generic batteries? 4. Is there an easy way to get all the cells back to a balanced voltage without any special equipment? 5. Is it worth bothering with the above or should I buy a replacement for $80 off of Aliexpress and take advantage of an advertised 1 year warranty for when it inevitably fails again a few months down the line? Link to comment Share on other sites More sharing options...
Keith Posted April 25, 2016 Share Posted April 25, 2016 49 minutes ago, GameKing said: My questions are the following: 1. Does the charger/BMS know when there are bad cells and account for this so that the remaining cells aren't overcharged or damaged? Not exactly - depending on the way the BMS functions it is likely that it just shunts the current around cells when they reach full charge, it will certainly make attempts to stop any cell from going above 4.2V. 2. Is there a way to jumpstart the individual "dead" cells while they're still in series with the others? No, whether or not they are in series with the others, unlike NiCads which could be kick started, Lithiums degrade in a much more terminal way. 3. Is it safe to remove and replace the dead cells with new ones/ Does anyone know if the cells are typically soldered in or attached in a semi-permanent way on these generic batteries? Depends upon the battery manufacturer, many are tagged and those tags are soldered into the BMS, so those can be desoldered and changed (buying tagged ones to do so) some are spotwelded together and need the right equipment. Is it worth doing? Almost certainly not as the others are likely to be not far behind and, of course, it is just as likely they are all at lower capacity and not just a few. 4. Is there an easy way to get all the cells back to a balanced voltage without any special equipment? Leaving the charger on for several hours after it shows complete will usually continue to trickle charge the lower voltage cells and help bring them up but do keep an eye on it though. I suspect it will not make a huge difference. 5. Is it worth bothering with the above or should I buy a replacement for $80 off of Aliexpress and take advantage of an advertised 1 year warranty for when it inevitably fails again a few months down the line? A replacement is probably the way to go - consider going for a higher capacity (say 260Wh) If you are happy otherwise with the wheel and if you have room to fit it as it will be less stressed and should last longer. Link to comment Share on other sites More sharing options...
Chriull Posted April 25, 2016 Share Posted April 25, 2016 Best solution would be some serious 16s2p pack. One possibility could also be, that your charger went bad or "decalibrated" - so it wont deliver the needed max voltage anymore. ad 1) As much asi know by know about BMS/balancing @Keith formulation "it will certainly make attempts to stop any cell from going above 4.2V." Is right, but the BMS has no chance to do so - especially with 3-4 "dead" cells the rest has a big probapility to get seriously overcharged. ad 5) /sarcasm on: good luck with the one year warranty /sarcasm off. Link to comment Share on other sites More sharing options...
OhPardonMe Posted April 25, 2016 Author Share Posted April 25, 2016 Thank you @Keith and @Chriull for the responses. I'm otherwise happy with the wheel for the money that I spent on it. Would love something faster but can't justify the investment at this point in time. Do you both agree that bad individual cells would cause the symptoms I'm experiencing? 57 minutes ago, Keith said: A replacement is probably the way to go - consider going for a higher capacity (say 260Wh) If you are happy otherwise with the wheel and if you have room to fit it as it will be less stressed and should last longer. I would love to get something that lasts longer, but there's no room for anything bigger without a case modification. I could theoretically get a 174Wh battery which I understand has the same footprint. 2. Is there a way to jumpstart the individual "dead" cells while they're still in series with the others? No, whether or not they are in series with the others, unlike NiCads which could be kick started, Lithiums degrade in a much more terminal way. I've seen methods in certain videos where the person uses a 9 volt battery and applies it to the dead cell for a certain amount of time in order to get it up to a voltage where to will accept a charge again, then trickle charge it to full capacity. If this was possible, would the cell capacity still be significantly affected because of the fact it was previously "dead"? 43 minutes ago, Chriull said: One possibility could also be, that your charger went bad or "decalibrated" - so it wont deliver the needed max voltage anymore. How would I test this theory? Simply hooking up a multimeter to the charger and looking at the output voltage? ad 5) /sarcasm on: good luck with the one year warranty /sarcasm off. You're probably right, but it depends on where you buy. eBay is excellent with matters like this. If they advertise a warranty then fail to honor it, the listing is not as described and eBay will guarantee your money back. Sellers are much more concerned about their feedback rating, so will go to great lengths to avoid a negative feedback. Never bought from Aliexpress though, so I'm not sure whether it's the same, but it looks like they have similar buyer protections in place. Link to comment Share on other sites More sharing options...
Chriull Posted April 25, 2016 Share Posted April 25, 2016 43 minutes ago, GameKing said: One possibility could also be, that your charger went bad or "decalibrated" - so it wont deliver the needed max voltage anymore. How would I test this theory? Simply hooking up a multimeter to the charger and looking at the output voltage? Yes. Should be around 67.2v. The second test would be the constant current ability - ?around 2A?. !Attention - not 100% sure if the charger will survive the following: just shortcut it with the ampere meter. Could blow the fuse of the amperemeter or overpower the charger. Safer would be some ~10 ohm resistor in serie with the according wattage. (Around 20w for the resistor to survive) the 20w could be expensive and difficult to become. I'd take a smaller wattage, make a short measurement before the resistor burns off (somewhere outside) ? Ps.: the easiest for current measurement is to just use the battery as load! No safety concerns and no burning. Just be very careful and safe that you do NOT shorten the battery! Link to comment Share on other sites More sharing options...
jer Posted April 25, 2016 Share Posted April 25, 2016 If the battery is old and well used, its time for a replacement. It's knackered. Jer Link to comment Share on other sites More sharing options...
OhPardonMe Posted April 25, 2016 Author Share Posted April 25, 2016 4 minutes ago, jer said: If the battery is old and well used, its time for a replacement. It's knackered. Jer I bought the unicycle in September of last year. Didn't use it too often, I'd estimate no more than 100 miles in total (at ~2-3 miles per charge). There were definitely month long stints in between where I didn't use it at all, so maybe improper storage (I never kept track of what charge level I left the battery at when not in use) has contributed to the failure, but I don't think it should fail within a year in any case. Link to comment Share on other sites More sharing options...
Keith Posted April 25, 2016 Share Posted April 25, 2016 22 minutes ago, GameKing said: I bought the unicycle in September of last year. Didn't use it too often, I'd estimate no more than 100 miles in total (at ~2-3 miles per charge). There were definitely month long stints in between where I didn't use it at all, so maybe improper storage (I never kept track of what charge level I left the battery at when not in use) has contributed to the failure, but I don't think it should fail within a year in any case. You would hope a battery would last a damn sight longer than that but...... Cheap wheels often have cheap cells in them - sometimes even used cells, just using cells that are not well matched can be enough for a few to get too low in voltage, particularly if the BMS is not very sophisticated - so a not great battery in the first place is one possibility. Assuming it's a 350 Watt motor it probably can still pull peaks of 500 Watts which would draw around 9 Amps which is a lot from a 2200mAh cell, that is why both @Chriull and I suggested you might want to get a larger capacity pack. regularly discharging it all te way to empty ages them fast as well, but it sounds like you haven't done that. Leaving a Lithium battery either fully charged or fully discharged for long periods can age it significantly, but not so as it would fail in 6 months. @Chriull's suggestion that, actually it might be the charger is also a good one to check (which I forgot as a possibility :-0 ) As to "is it definitely bad individual cells" - really I'd say it's 50:50 whether all or many of the cells have lost capacity or a rew have failed, it really sort of comes down to how well the battery was made in the first place. Although, probably less likely, it might possibly also be a fault in the BMS (which is part of the battery.) You would only really know for sure if some cells were faulty by part discharging the battery (go for a mile or so ride) and then opening the battery and checking the voltage across each cell, usually each cell can be seen to terminate on the BMS circuit board so can be checked there. With any testing or repairing you do, please do not lose sight of the massive currents and quite high voltages these batteries can deliver, It is not a high enough voltage to electrocute you but shorting across the positive and negative, for example whilst checking the pack voltage with a multimeter will be like using an arc welder and could generate a lot of heat. Link to comment Share on other sites More sharing options...
US69 Posted April 25, 2016 Share Posted April 25, 2016 It Is also possible that your Wheel Is missing a correct balancer function?! can be on generic wheels... as normally if there Are Bad Cells The Bms would stop functioning at all...also can be your Charger Is defect ...everything Is possible!!! i would say: Go for a new pack...where Are You from??? Europe or States?be Link to comment Share on other sites More sharing options...
OhPardonMe Posted April 25, 2016 Author Share Posted April 25, 2016 8 minutes ago, KingSong69 said: It Is also possible that your Wheel Is missing a correct balancer function?! can he on generic wheels... as normally if there Are Bad Cells The Bms would stop functioning at all...can be your Charger Is defect ...everything Is possible!!! i would say: Go for a new pack...where Are You from??? Europe or States? I'm from the states. Now that you mention it, the charger started acting up a couple days ago. It was working seemingly normally with the decreased battery function (i.e. Plug it in, would go red for x minutes then turn green to indicate a full charge. Then, unplugging it, only 3 lights would come on. A couple days ago, plugging the charger in, it does not want to charge, the light would just stay green. I got it to start eventually by toggling the unicycle on an off repeatedly. Is this indicative of the BMS cutting out because of the bad cells or a charging issue? Link to comment Share on other sites More sharing options...
Keith Posted April 26, 2016 Share Posted April 26, 2016 8 hours ago, GameKing said: Is this indicative of the BMS cutting out because of the bad cells or a charging issue? The short answer is "Yes". You would need to measure the output from the charger to know. See also the below thread, although, in this case it is a new battery that was pushed to very low power and the IPS is different from most other wheels in having the BMS in the main control board so it may be cleverer than most, it does show how a single failed cell can behave: Link to comment Share on other sites More sharing options...
checho Posted April 30, 2016 Share Posted April 30, 2016 On 4/25/2016 at 10:53 AM, GameKing said: I have a generic unicycle with a generic 130Wh battery (16 2200mAh cells in series). Over time, the battery life has degraded significantly to the point where if I charge it now, no more that 3 of the 4 LED's will turn on when the battery is fully charged, and I can't get more than 1km of distance out of it. Someone correct me if you think it may be something else, but I believe that 3-4 of these cells have died which brings the fully charged voltage of the overall battery down to ~50 Volts (I haven't gotten access to a multimeter to confirm this), and the BMS will cut it off even though the 12-13 good cells still have most of their charge left. My questions are the following: 1. Does the charger/BMS know when there are bad cells and account for this so that the remaining cells aren't overcharged or damaged? 2. Is there a way to jumpstart the individual "dead" cells while they're still in series with the others? 3. Is it safe to remove and replace the dead cells with new ones/ Does anyone know if the cells are typically soldered in or attached in a semi-permanent way on these generic batteries? 4. Is there an easy way to get all the cells back to a balanced voltage without any special equipment? 5. Is it worth bothering with the above or should I buy a replacement for $80 off of Aliexpress and take advantage of an advertised 1 year warranty for when it inevitably fails again a few months down the line? When the battery pack is bad the only method to rescue bad cells is to take the pack appart get a charger that will trickle charge when the battery is below certain voltage in other words a special charger to revive bad cells individually, and then test each cell individually. To test the cell you could discharge the cell and measure the energy provided by the cell. Some will have to be discarded, some could be revived with reduced capacity. Then the discarded cells can be replaced by good ones. It will not be possible to revive the pack as a whole. To try to revive the pack as a whole which is not going to be as reliable as charging and testing cells individualy, what you could do is apply a very low charge current and charge the pack to 68.8v overcharge a little so that the bms does its job, and use a very small current to prevent the bad cells from overheating, this may help revive the pack to some degree. Link to comment Share on other sites More sharing options...
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