Knifa Posted November 8, 2017 Share Posted November 8, 2017 Hey there, I picked up a Ninebot One S2 on eBay and had a great time riding it over the last couple of days. However, I've noticed that in trying to charge it, only one battery side seems to charge. If I unplug the battery on the good side, when plugging in the charger the LED doesn't change at all. Stays totally green. I'm still struggling to get into the side with the one that isn't charging (these plastic tabs are insane!) so haven't tried disconnecting/reconnecting it yet. On the app, everything shows normal (though with both batteries in, it complains they are out of balance understandably) Any ideas on what it could be? Is this battery toast? Cheers! Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 Don't think I can edit my posts? Managed to get the cover off. Everything looks OK inside. One thing I noticed is that the battery on the good side has a blinking green LED, whereas it's solid on the other one. Plugged it in to charge. Battery LED is now flashing red. Charger LED only stayed red for a little bit but back to green. Looking at the app, I'm guessing the cells inside are maybe unbalanced. "Battery cell of battery 2 is in a big differential pressure." Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 8, 2017 Share Posted November 8, 2017 4 minutes ago, Knifa said: Don't think I can edit my posts? Editing is just possible for some limited time. 4 minutes ago, Knifa said: Managed to get the cover off. Everything looks OK inside. One thing I noticed is that the battery on the good side has a blinking green LED, whereas it's solid on the other one. Be very carefull - if you get your second battery pack „online“ again there could be quite some voltage differrence between the two packs which could lead to enourmous currents to equalize them... this could in the worst case lead to burning battery cells! Both packs are secured by a bms (battery managment system) which can cut-off the input side and/or the output side. As long as the batteries are „unbalanced“ (have different voltages) one of the packs will always be „cut-off“ by its bms. there could be a connector problem with one of the packs? does the s2 have fuses, where one could have melted? The s2 has imho some logic/communication between the bms and the mainboard? Maybe there is somthing wrong, or there is some diagnostic available by the app? 1 Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 Connectors look OK, not too sure if there are fuses anywhere. The only thing the app tells me is that the battery is unbalanced. It weirdly still states that battery status is "normal" so I'm not too sure what the deal is, hah. Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 8, 2017 Share Posted November 8, 2017 50 minutes ago, Knifa said: However, I've noticed that in trying to charge it, only one battery side seems to charge. If I unplug the battery on the good side, when plugging in the charger the LED doesn't change at all. Stays totally green. 14 minutes ago, Knifa said: Looking at the app, I'm guessing the cells inside are maybe unbalanced. "Battery cell of battery 2 is in a big differential pressure." The one battery not charging is battery 2? “in big differential pressure“ should mean the voltages of the cells in this pack have different voltages. This normaly is prevented by leaving the charger plugged into the wheel for some hours after the charging process is finished. So maybe sou have good luck if you charge the wheel with just the unbalanced pack installed, also the charger led shows no charging. but unfortionately some wheels are known to balance quite insufficiently. You‘ll see if your pack can be revived by this... Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 I'll leave it on for a while and see if it sorts itself out. I swapped battery sides to see if it made a difference but it looks like it's the battery itself. Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 I have been unplugging it right away as it turns green. Could that have caused problems? Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 8, 2017 Share Posted November 8, 2017 1 minute ago, Knifa said: I have been unplugging it right away as it turns green. Could that have caused problems? Yes - but not already after a couple of days/some charges. Becoming unbalanced takes longer... so presumably the cells in this one pack already were in a „bad/not so good“ condition, or there are, as mentioned before other probs. (Connectors looking ok tells as good as nothing about their state, for example...) Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 I will leave it on and hopefully it comes back alive! Since it does the same thing when swapping sides, the problem must be the battery. Do you know where I can purchase replacement batteries at all if it comes to it? Spare parts for the S2 seem very difficult to find. Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 8, 2017 Share Posted November 8, 2017 3 minutes ago, Knifa said: I will leave it on and hopefully it comes back alive! But with just the "bad" battery pack inside! 3 minutes ago, Knifa said: Since it does the same thing when swapping sides, the problem must be the battery. So the good battery works and can be charged at both sides, the bad one at no side? 3 minutes ago, Knifa said: Do you know where I can purchase replacement batteries at all if it comes to it? Spare parts for the S2 seem very difficult to find. With some bad luck just at official segway shops? Speedyfeet has it listed as out of stock on his website... Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 The good battery works on both sides, yep. The bad battery doesn't work on either side. No listing on the Segway shop site. I've sent them a ticket so maybe they can be of use. Even a google for "Ninebot One S2 battery" only gives Speedyfeet. Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 One of the weird things is that even though it lists low capacity (e.g., 7%) the voltage is still at charged level --- the same as the good battery. Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 8, 2017 Share Posted November 8, 2017 12 minutes ago, Knifa said: One of the weird things is that even though it lists low capacity (e.g., 7%) the voltage is still at charged level --- the same as the good battery. If this pack is really unbalanced, but shows normal full voltage (4,2V x 15 or 16 cells) this would mean, that some cell has to have above 4,2V. So again be carefull with this pack - also with the balancing charge you just give him. Don‘t leave this unattended. Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 8, 2017 Author Share Posted November 8, 2017 The battery seems to have fully drained (from the point of the BMS). Light is blinking red, unit won't power on. I'm not sure the charger is doing anything at all. I think she may be dead. I've started the return on eBay --- hopefully they will take it back even though I have scuffed it up a bit more. Quote Link to comment Share on other sites More sharing options...
Popular Post Knifa Posted November 8, 2017 Author Popular Post Share Posted November 8, 2017 (edited) I think I fixed it! Against better judgement, my friend and I took the battery apart. There is one main board inside (the BMS, presumably) and a daughterboard that helps connect the two rows of batteries. There are 15x 18650 Li-on cells, at 4.2V when charged. You might spy from the picture of the BMS board, that there is a hidden push button on there. My LED was originally flashing red (totally flat?). I pushed it once, and it turned solid green for a few moments, and then back to flashing red. A few moments later I tried holding it down, and it started blinking green, and then back to blinking red. Since then, the button does absolutely nothing. No idea what the LED codes mean, nor what this button is for. We inspected the cells and found all to be fully charged (4.2V) bar one --- the very first cell in the bottom row, which was at 2.8V. Total speculation but, before the LED turned blinking red, it was previously solid green. We were wondering that, perhaps, the BMS is powered from the first cell on pack. Over time, maybe it's just really drawn out this battery? Next step was to try and charge this low cell. We used a good charger (iSDT SC-608), and some patience, to poke at the two accessible battery tabs with a pair of multimeter probes. As soon as the cell hit 3V, the LED instantly turned solid green again. After about 45 minutes of holding it like this (ouch) the cell charged up fully without any problems. No heat build up, even when charging at 3A. After all this, we plugged it back into the Ninebot. No more complaints from the app or machine! Reports 100% charge from the battery. I ran it around a bit to see if the cell was dropping off too quickly, but it appears to be totally fine. Voltage drops in line with the other cells. I suspect the cell may still be a bit goofed, but at the very least it looks like it's easy(ish) to replace. Edited November 8, 2017 by Knifa 2 5 Quote Link to comment Share on other sites More sharing options...
Popular Post Keith Posted November 8, 2017 Popular Post Share Posted November 8, 2017 @Knifa, excellent piece of investigation. I would seriously hope that Ninebot wouldn’t have been powering the BMS from one of the cells, so it might be possible that the cell is beginning to fail (after all, why did the other battery pack not also have one very low cell?). However, almost anything is possible so it might be as you say ?. It is also good to know that the BMS is clearly monitoring all the cells. Just a reminder for anyone else reading this well documented fix and intending to check their own possibly faulty battery. Do not forget that there is an awful lot of energy in these batteries, if you do open up a battery pack be very, very careful that you do not short circuit anything, for example while using a multimeter to measure voltage. The current that may be discharged can exceed an arc welder and do considerable damage or even result in a fire. 1 5 Quote Link to comment Share on other sites More sharing options...
Popular Post Knifa Posted November 8, 2017 Author Popular Post Share Posted November 8, 2017 (edited) Thanks @Keith! It was a wild ride. Taking apart the casing is pretty sketchy now that I've seen the inside --- very easy to poke at something with whatever you're using to pry it open. My initial thought on powering the BMS was that down-regulating 63V to <5V must be a pretty insane task. I looked into it a bit further and it turns out you can get >50V to <5V switching regulators in a single IC package, while still being pretty efficient. It would be pretty silly of them not to use the entire pack, though it would be more straightforward to just use a single cell (but that doesn't account for the other one being fine). I'm still confused as to what the blinking means. The other pack still has a blinking green LED while this one is solid green. Both have the same BMS firmware version. What does the button do? Why doesn't it work anymore? So many questions! Information and parts for the S2 seems really slim going, which is a shame because it seems pretty great in general. Edited November 8, 2017 by Knifa 3 1 Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 9, 2017 Author Share Posted November 9, 2017 Looking at the pictures again, I've noticed that the solder job on the battery is like... really weak. Are half of these not even soldered properly or what? Quote Link to comment Share on other sites More sharing options...
Popular Post Chriull Posted November 9, 2017 Popular Post Share Posted November 9, 2017 7 hours ago, Knifa said: Looking at the pictures again, I've noticed that the solder job on the battery is like... really weak. Are half of these not even soldered properly or what? Mabye they are just soldered from the other side and the blobs seen here is just the tin that came through? 1 3 Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 9, 2017 Author Share Posted November 9, 2017 2 hours ago, Chriull said: Mabye they are just soldered from the other side and the blobs seen here is just the tin that came through? I hope so! Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 10, 2017 Author Share Posted November 10, 2017 After riding a lot today, I've ran into the same problem. We're going to try replace the cell so I'll post up how it went soon! The existing cells inside are made by LG and have the identifier LGABMG11865. They're 2850mAh 10A cells, and I think the series is called MG1. These are turning out to be pretty tricky to get a hold of on the UK so we'll need to put one with a larger capacity in. Thankfully, it looks like the BMS uses the lowest cell voltage to give a capacity remaining for the whole battery, so as long as it's close enough it should be fine. 1 1 Quote Link to comment Share on other sites More sharing options...
US69 Posted November 10, 2017 Share Posted November 10, 2017 (edited) 26 minutes ago, Knifa said: After riding a lot today, I've ran into the same problem. We're going to try replace the cell so I'll post up how it went soon! The existing cells inside are made by LG and have the identifier LGABMG11865. They're 2850mAh 10A cells, and I think the series is called MG1. These are turning out to be pretty tricky to get a hold of on the UK so we'll need to put one with a larger capacity in. Thankfully, it looks like the BMS uses the lowest cell voltage to give a capacity remaining for the whole battery, so as long as it's close enough it should be fine. For sure, this low cell which had 2,8Volt is defect! It is not just for fun at this low voltage, you should have changed it from the start on ;-) There are a lot of cells you can choose from. Most important part is: This cell also must have the same max continuos amperage draw than the other cells, whiich i guess is 10Amp per cell! Thats much more important than hitting the same amount of „mah“... No problem when the batterie is abit higher in mah...but it is imporatnt it can stand the 10Amp... Perhaps this: https://www.nkon.nl/rechargeable/18650-size/lg-inr18650mh1-3200mah-3c-battery.html or https://www.nkon.nl/rechargeable/18650-size/samsung-inr-18650-30q-3000mah-button-top.html or a Panasonic 18650pf might be ok.....( the PF would be the best by numbers if you can not get the MG1) And your BMS has done it completely correct...with such a different in voltage it is important, that it stops working :-) and no, it is not only relying on this „first“ cell :-) Edited November 10, 2017 by KingSong69 3 Quote Link to comment Share on other sites More sharing options...
Popular Post Knifa Posted November 12, 2017 Author Popular Post Share Posted November 12, 2017 (edited) So today we replaced the cell and, again, it seems to work! I also got some more information on the BMS during this so see below for details. We measured the suspect cell (1, bottom left). It read 3.4V, where the other cells were reading 3.8V. Definitely a damaged/failing as mentioned above --- so it was time for it to come out. First step was to liberate the cells and boards from the casing. Thankfully, nothing is glued down and everything is screwed in place with nice holders, etc. There are a good few screws, all covered in silastic, however if you squeeze hard enough with a screw driver (philips), they will twist out. We also had to tear away the silastic around the XT60 and BMS comms cables. Once that's done, the whole thing just kinda lifts out. With this, we can get a look at the back of the BMS board. The chip on the back here is the actual BMS IC. It's a TI BQ7694003 (datasheet) which is a series of battery monitor ICs providing current monitoring, short circuit protection, low voltage protection, yada yada. The chip on the front of the BMS board is a STM 8L151K6T6 (datasheet) which is a basic 8-bit MCU, presumably doing comms with the main board and handling the BMS IC. There are also two MOSFETs (following the design from the BMS IC datasheet, I guess) one of which is 100V 40A (MDD1902) and the other was larger but I couldn't read the numbers off. Some interesting tidbits from the BMS IC: There's mention of a SHIP/NORMAL mode (low power for shipping vs. normal operation) and a button shown in the example circuit. Maybe this is what the button is for? The IC is capable of balancing using either its own internal drivers or externally (I guess a whole ton of external MOSFETs like a normal charger?). In this case, it looks like Ninebot have opted to use the internal drivers as there isn't really anything else on the board. Internal balancing is limited to 50mA which is gonna be hella slow --- is this what happens during trickle charging? Balancing is controlled by the host (the STM) rather than by the BMS IC After that adventure, we ripped the dud cell out. We pried at the welding tabs with a stanley knife until it simply came free. There is enough room to get in there (at this edge cell, at least) however I'm not sure what it would be like trying to do it in the center. The plastic casing around the batteries is weirdly flexible so it makes it pretty nice to work with. At this point, the LED started blinking red (surprise!) which at least confirms it's not pulling all power from one cell. Pushing the tab back into the battery made it turn a happy green. With the cell gone, it was time to put in our new cell. The new cell is a LG HG2 Series 3000mAh from Amazon directly, which fits the bill for this perfectly. As far as I could tell, the HG2 is the step up from the cells that are already in this. The chemistry is the same (INR) and it provides the same/higher constant discharge rates so all seems good. I should have really double checked the capacity at this point, to make sure it was legit and not a fake, but some visual checks (plus coming straight from Amazon) made me feel OK. If I was doing it again, I would double check. I didn't get any pictures of the soldering process, unfortunately, but the gist is this: We used a good temperature-controlled soldering station (Hakko 888D) with a very large tip, good solder (MG 63/47), and good flux (MG liquid something...). The iron was set to 450C. The positive and negative sides of the battery were tinned with a reasonable dollop of solder, after applying a lot of flux. We double checked for heat at this point, and the battery didn't get hot at all. With lots of flux on the tabs, the battery was placed in the plastic holdery-thing and held firmly in place. The positive end was soldered first (near the BMS board). My friend pushed the tab firmly towards the battery with a stick while I gave it a quick tap with the soldering iron. Repeat above for the other end. The battery had a warmth to it afterwards but not warm enough to count as "hot". The light started flashing green again, so seems like everything went together well. After this, we basically did everything in reverse. Everything back into the casing, screws all in, bit of hot glue to make up for the missing silastic. Nothing in particular to report here. Once all back together and screwed into the Ninebot (on it's own, other battery disconnected), it all seemed to work OK! No shouting from the app, reporting around 60% capacity. I rode it around for a good bit, then to the store and back, and it seems to be dropping at a fairly reasonable rate. Battery temperature also reports reasonable temps, no huge voltage sag, etc. So that's it! All seems to be in working order, for now. That said, a couple of things still to test: Run the battery to near empty, and charge it up again. Haven't tried charging it with this new cell yet. Test with the other battery installed. Do they drop in capacity at the same rate? Go through a couple of cycles, crack open the battery again and check cell voltages. Are they all within reasonable limits? Edited November 12, 2017 by Knifa 5 Quote Link to comment Share on other sites More sharing options...
Chriull Posted November 12, 2017 Share Posted November 12, 2017 @Knifa:thats what happens while balancing ( "trickle charging") - this ~50mA are lead around the charged cells and just go through the cells still in need of charge (lower voltage). Unfortionately there are quite some limits how many and which cells can be bypassed (at least with the controller the ninebot one e+ used for the bms) and also this just internal balancing is quite limited (power dissipation inside the ic) - "active" balancing with external mosfets has more abilities... There where some (quite qualified) reports that the ninebot one e+ bms with just internal balancing did not get it. Maybe also sonething in the balancing circuit has gone bad, so this one cell gets all over the time bypassed by the controller (partially)? However, great report and have fun driving! 1 Quote Link to comment Share on other sites More sharing options...
Knifa Posted November 15, 2017 Author Share Posted November 15, 2017 (edited) @Chriull it's interesting that they state in the manual that when the charger is green (trickle charging) that the machine is good to go. Balancing is really important! I guess with good cells though, they should all drop in line (it probably stops the fast charging once at least one cell has hit the max voltage?) In this case, it looks like the cell was just bad. With the new cell everything charges OK and with the good pack in, they fall to the same capacity. Previously, the one with the bad cell would drop much quicker than the other. I checked the cell after charging (including a long time on the trickle charge) and it was sitting at 4.1v, with the rest at 4.2v. This makes sense as the capacity is higher (but it should still try balance it out?) Also instead of returning to the eBay seller, they gave me a great discount for the battery issue, so all is well. Thanks for following the journey! Edited November 15, 2017 by Knifa 2 1 Quote Link to comment Share on other sites More sharing options...
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