Chriull Posted December 19, 2016 Share Posted December 19, 2016 At one of my last recherches i found at http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures the following paragraph: "Matched cells with identical capacities play an important role when discharging at low temperature and under heavy load. Since the cells in a battery pack can never be perfectly matched, a negative voltage potential can occur across a weaker cell in a multi-cell pack if the discharge is allowed to continue beyond a safe cut-off point. Known as cell reversal, the weak cell gets stressed to the point of developing a permanent electrical short. The larger the cell-count, the greater is the likelihood of cell-reversal under load. Over-discharge at a low temperature and heavy load is a large contributor to battery failure of cordless power tools" i can't really follow this cell reversal thing in detail (by now), but since this site seems to be a serious source for in depth battery knowledge i tend to trust their conclusion... Link to comment Share on other sites More sharing options...
FreeRide Posted December 20, 2016 Share Posted December 20, 2016 The site is pretty good, but one should remember a couple things. It mostly has information from a Industrial Supplier of Battery Analyzers, they have a commercial interest. Some of the quoted studies are more than 10 years old. Some information is missing as can be expected. Still the basics are there although I remember in the past errors were found, I don't know if they have all been corrected. Never hurts to double check. From the article you quote the most important thing is the general idea. If your cells in the pack are not matched and you start stressing them you are going to more quickly and more acutely create the conditions where the problems of unmatched cells are present. This is a big mistake of people building their own packs using random cells, or cells they have bought from different vendors that are of different ages, and have not been test with an analyzer before being put together in a pack. The best packs have as closely matched batteries as possible. As I noted in another thread that does not just mean just the same theoretical or typical capacity, or the capacity tested at 2A or 10A discharge, it means they a have been checked for the same power output (E*I) at various discharge rates. Ideally batteries in a pack should be from the same manufacturing lot which is labeled on the cells for pack manufacturers. The manufacturer actually does a lot to ensure batteries from the same lot have matched performance characteristics (were talking the quality big name makers here). Li-Ion batteries go through conditioning before they are sold to reseller and pack manufacturers. Link to comment Share on other sites More sharing options...
HermanTheGerman Posted December 20, 2016 Share Posted December 20, 2016 Though the above may be right, I don't fear for my accus in the wheel. First I keep the wheel in a room which has never less than 20 degrees, and second, during riding the batteries are heated by delivering their current to the motor. I had once a ride of 22 km at -4 degrees, and the Kingsong app showed a battery temperature of 22 degrees, and thats the lowest value I have ever seen until now. But yes, I wouldn't leave it outside at low temperatures while not using it. Link to comment Share on other sites More sharing options...
steve454 Posted December 20, 2016 Share Posted December 20, 2016 2 hours ago, Chriull said: Over-discharge at a low temperature and heavy load is a large contributor to battery failure of cordless power tools" Yes, but do they have a battery management system? EUC's will not let you overdischarge unless you keep turning them off then on again, and even then the good one's will stop you from riding until you recharge. However, I agree that the batteries should not be discharged too much. It stresses the batteries, at 20% is where i have read that Ninebot goes in to low speed mode to save the batteries, but you can still ride for some miles, but it's not good to do that. I did that one time just to see what it would do, it is not fun to be limited to such a low speed, but it will let you get back home slowly. I wonder if anyone has tried to really keep going until the batteries are almost dead, and if they would recharge? Link to comment Share on other sites More sharing options...
FreeRide Posted December 20, 2016 Share Posted December 20, 2016 39 minutes ago, steve454 said: Yes, but do they have a battery management system? EUC's will not let you overdischarge unless you keep turning them off then on again, and even then the good one's will stop you from riding until you recharge. However, I agree that the batteries should not be discharged too much. It stresses the batteries, at 20% is where i have read that Ninebot goes in to low speed mode to save the batteries, but you can still ride for some miles, but it's not good to do that. I did that one time just to see what it would do, it is not fun to be limited to such a low speed, but it will let you get back home slowly. I wonder if anyone has tried to really keep going until the batteries are almost dead, and if they would recharge? You're riding along and one cell in the pack has a problem, at 5A draw it only holds a voltage of 3V but the other cells are better and they are outputting 3.7V. What can the battery management system do? The total voltage of the pack is still good. That one sell is cooking though, maybe the BMS is watching every cell (maybe not), but if it is and it sees that that there is a problem what is it going to do? Shut down? The article is talking about when the packs are not working correctly because the extra stress has caused one of the cells to have different characteristics than the others in the pack. Chances are even outside of the stressed condition it is still stressed and will eventually fail, but not as fast and maybe not as critically. the protection circuits will eventually have to kick in and that is trouble for you since there is no redundant power source. Nothing you can do about it, but if your battery pack is aging, try not to stress it or have it tested at the cell level (Not usually possible with the EUC packs). Their only recommendation is don't over stress the batteries and cold weather and continuous high drain are a couple of ways to add extra stress, combined (which may happen in a EUC) could be serious and could cause a week cell to fail. Link to comment Share on other sites More sharing options...
US69 Posted December 20, 2016 Share Posted December 20, 2016 5 hours ago, HermanTheGerman said: Though the above may be right, I don't fear for my accus in the wheel. First I keep the wheel in a room which has never less than 20 degrees, and second, during riding the batteries are heated by delivering their current to the motor. I had once a ride of 22 km at -4 degrees, and the Kingsong app showed a battery temperature of 22 degrees, and thats the lowest value I have ever seen until now. But yes, I wouldn't leave it outside at low temperatures while not using it. the temperature you see in the app has nothing todo with batterie temperature... Its measuring the board temperature! Link to comment Share on other sites More sharing options...
HermanTheGerman Posted December 20, 2016 Share Posted December 20, 2016 1 hour ago, KingSong69 said: the temperature you see in the app has nothing todo with batterie temperature... Its measuring the board temperature! R u sure ? Because the Kingsong app shows in the battery detail display explicitely the text "battery temperature". Of course I don't know where the sensor really is, but I would have trusted the app. Link to comment Share on other sites More sharing options...
FreeRide Posted December 20, 2016 Share Posted December 20, 2016 If it's a good pack it should have temperture sensors in the pack for safety reasons during charging and discharging. I sure hope such critical power packs have multiple temperture sensors. Link to comment Share on other sites More sharing options...
US69 Posted December 20, 2016 Share Posted December 20, 2016 51 minutes ago, HermanTheGerman said: R u sure ? Because the Kingsong app shows in the battery detail display explicitely the text "battery temperature". Of course I don't know where the sensor really is, but I would have trusted the app. Appsolutly! There is no way to measure the battery temperature...and the BMS System is not even connected to the board for data Transfer! The measurement is for the board...and really important for the Mosfets sitting on it! Over 70 degree you can have a Mosfet burned.... @FreeRide No battery pack that i know has temperature measurement! The BMS is for over-under-voltage and what not...but not measuring temperature! Link to comment Share on other sites More sharing options...
FreeRide Posted December 20, 2016 Share Posted December 20, 2016 If there are no temp sensors in the battery pack being monitored during charging and operation then this is something that is a serious omission and show the battery system on these devices are not very sophisticated. Even consumer chargers for industrial 18650 monitor temperature, and good packs like for quality tools monitor temperature. I don't know about shutdown but an EUC should refuse to start if temperature is above a safe limit and charger should reduce current if the pack is above a safe temperature. Most of the chargers for these things are quite lame and likely can't really heat a pack unless it is faulty, but a few of the so called fast chargers do reach a pretty good charge rate. Still temperature monitoring is important, and I'm surprised if they don't have it even externally if not internally. To follow manufactures specifications temperature must be monitored too ensure a proper service life as the ambient can carry a lot for something like this that is used outdoors. Link to comment Share on other sites More sharing options...
Chriull Posted December 20, 2016 Author Share Posted December 20, 2016 1 hour ago, KingSong69 said: @FreeRide No battery pack that i know has temperature measurement! The BMS is for over-under-voltage and what not...but not measuring temperature! @Craniumanalysed the ninebot one e+ BMS and there is one tempurature sensor at the battery cells... Link to comment Share on other sites More sharing options...
US69 Posted December 20, 2016 Share Posted December 20, 2016 1 hour ago, Chriull said: analysed the ninebot one e+ BMS and there is one tempurature sensor at the battery cells... Ok...my fault then! But whatsoever: this temperature measurement is when at all only useful as charging protection. For what should it be needed in Operation? Cutting the power, so we faceplant when battery is to warm or to cold? Nobody would want that :-) At all this chip -if i be nitpicky- will only measure the BMS-Board temperature...but not the 16-32cells in any way And: As There is no communication between BMS and board...it is in now way possible this is shown in the app. Link to comment Share on other sites More sharing options...
Chriull Posted December 20, 2016 Author Share Posted December 20, 2016 10 minutes ago, KingSong69 said: Ok...my fault then! But whatsoever: this temperature measurement is when at all only useful as charging protection. For what should it be needed in Operation? Cutting the power, so we faceplant when battery is to warm or to cold? Nobody would want that :-) At all this chip -if i be nitpicky- will only measure the BMS-Board temperature...but not the 16-32cells in any way And: As There is no communication between BMS and board...it is in now way possible this is shown in the app. Exactly. The BMS is mainly to protect the battery cells (and some of the measures/implementations are a bit questionable) and to faceplant the rider... Link to comment Share on other sites More sharing options...
esaj Posted December 20, 2016 Share Posted December 20, 2016 Some BMSs indeed seem to have temperature protections (either only overtemperature or over- & undertermperature), but it would seem they only cut the power from charge/discharge -side, not reporting it to the mainboard: Link to comment Share on other sites More sharing options...
US69 Posted December 20, 2016 Share Posted December 20, 2016 The only wheel i know which has some more connectiong from BMS to the Motherboard than the discharge cables are the Inmotion wheels. These have more cables than the Standard discharge (+,-), but i did not know what they Report to the board... Link to comment Share on other sites More sharing options...
Vik's Posted December 20, 2016 Share Posted December 20, 2016 44 minutes ago, KingSong69 said: The only wheel i know which has some more connectiong from BMS to the Motherboard than the discharge cables are the Inmotion wheels. These have more cables than the Standard discharge (+,-), but i did not know what they Report to the board... Ninebot A1/S2 and MiniPro have data connection between the BMS and controller. Link to comment Share on other sites More sharing options...
HEC Posted December 20, 2016 Share Posted December 20, 2016 7 hours ago, KingSong69 said: @FreeRide No battery pack that i know has temperature measurement! The BMS is for over-under-voltage and what not...but not measuring temperature! Actually even the cheap basic BMS DO have ("internal" - e.g. not connected to CB) temperature sensors like this one: https://www.aliexpress.com/item/16S-60V-or-67-2-V-unicycle-lithium-ion-battery-BMS-60V-li-ion-battery-protection/32422681053.html The fact that BMS doesn't communicate the actual inner pack temperature to CB doesn't mean that it's incapable of measuring it and acting upon it as well. The other question is if you'd prefer to have a cut-off most likely resulting in faceplant or have the battery pack overheat (and maybe go up in the flames) but to continue supplying power to the wheel? Link to comment Share on other sites More sharing options...
Frode Posted December 20, 2016 Share Posted December 20, 2016 4 hours ago, HEC said: question is if you'd prefer to have a cut-off most likely resulting in faceplant or have the battery pack overheat (and maybe go up in the flames) but to continue supplying power to the wheel? Yes, this is the question. It's a true dilemma. Whatever you select it will hurt. The first one in your face. The second one in your wallet (and maybe even between your legs ). I'm not sure what I'd have selected, especially since I almost always wear protective gear which means it takes more before a faceplant hurts for more than just for a couple of hours. Maybe it is OK with the first time the battery is destroyed (and maybe even the wheel burns down). But what about the second time? Or third? Here in Norway I had to give $ 1600 for my KS-16 with the 840 Wh battery. My guess is that the battery is about half of the price (the 840 battery added $ 460 to the price from the standard battery, standard battery replaced and not delivered to me). That is a lot of money worth some protection and even a few hours of pain? Not? Or...maybe one should go for panzer instead of EUC... Link to comment Share on other sites More sharing options...
rdalcanto Posted December 20, 2016 Share Posted December 20, 2016 IMHO - Assuming you store and charge the EUC indoors, when in use, the batteries will stay warm enough because discharging them generates heat. Electric cars that are sitting outside below freezing have decreased range because energy is used to run the electric heaters in the cars, and energy is used to actively warm the pack in the beginning to improve performance and protect the cells. None of that applies to the EUC that is starting at room temperature. Link to comment Share on other sites More sharing options...
Slaughthammer Posted December 20, 2016 Share Posted December 20, 2016 8 hours ago, KingSong69 said: The only wheel i know which has some more connectiong from BMS to the Motherboard than the discharge cables are the Inmotion wheels. These have more cables than the Standard discharge (+,-), but i did not know what they Report to the board... Actually, all IPS Wheels manufactured within the last two generations have the BMS integrated into the control board, and therefore there is quite a bit of wiring between the pack and the board. All the time I've been curious about this one surplus wire going from the pack to the board, maybe it's a temperature sensor? However, battery temperature is not shown in the app. Link to comment Share on other sites More sharing options...
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