The 18650 Li-ion Battery pack Smart BMS mobile Apps software doesn't work via Bluetooth

[qiubosu]

1) I connected the 7S 30A Smart BMS, purchased from https://www.aliexpress.com/item/32840764349.html?spm=a2g0s.9042311.0.0.27424c4dJ6rzZ9, to a large 7S10P 18650 Lithium battery pack. The soldering, wiring and balance connection are all fine, and the Smart BMS can charge & discharge the battery pack.

The consistency of the battery pack isn't good, before 1st time charging, the voltage of one parallel group is 3.56V and the voltage of all the rest 6 parallel groups is 3.61V. When charging the battery pack with the Smart BMS, the voltage increase of the 3.56V parallel group is slower than that of the 3.61V parallel groups, e.g. when the voltage of the 3.56V parallel group increase to 3.71V, the voltage of the 3.61V increase to 3.84V, but this shouldn't be an issue, and I used a very simple charger I modified to particularly charge this lower voltage parallel group separately to make its voltage closed to that of the other parallel groups, to resolve the voltage consistency issue.

I install the recommended Bluetooth Apps onto my Huawei Android 5.1 smart phone. When run the Apps, it shows "The device can be connected" and "signal:Strong-22" etc information on my mobile, but can't see the Apps software dashboard screens as those in the supplier's advertisement listing. The Bluetooth PCB board connecting to the BMS PCB board has no light flashing either when running the Apps from my mobile. When go to Bluetooth settings for pairing, it displays "Couldn't pair with xiaoxiang BMS because of an incorrect PIN or passkey" and the Bluetooth PCB board has blue light flashing simultaneously for about 10 seconds.

2) I tried this on my Android 5.0 tablet also, and got "Pairing rejected by xiaoxiang BMS" when try to pair it. When run the Apps on my tablet, got the same displays as that run from my Android 5.1 Huawei smart phone, which has strong signal.

I installed both the old and new versions of the Apps for this Smart BMS onto my smart phone and tablet, but the smart BMS software dashboard screens don't work in each scenario.

The wiring, soldering, balance connection are all good, the resistance of each parallel group of battery cells are very closed, within the consistency range also, and the battery pack can charge and discharge, just the Smart BMS mobile Apps doesn't work.

This is an UART module to communicate to PC, but I didn't order this one, only the Bluetooth module.

3) I cleared the xiaoxiang Smart BMS Apps cache, then run the Apps again, a screen with elephant image shows up for a very short period of time, less than half second, then disappeared and changed to the screen with "Refresh" and "Fix" buttons, and with strong signal indication. Unplug & replug the Bluetooth PCB board from & into the Smart BMS PCB board, then run the Apps, but the software dashboard screens still don't show up. Charged the lower voltage parallel group cells to the voltage almost the same as the voltage of the other parallel groups cells, then run the Apps again, but the software dashboard still doesn't show up. Done some other different testing, but the software still doesn't work.

It is much appreciated if anyone has experience with this kind of Lithium battery Smart BMS and happened to the similar problems.

 

[amberwolf]

you might check these posts
https://endless-sphere.com/forums/search.php?keywords=xiaoxiang+app&terms=all&author=&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search
and other similar ones about the various bluetooth bms apps; they may help.

also, the bms is supposed to do the balancing of low cells like your pack started with, so if it is functioning you shouldn't have to manually charge it up. if it isn't doing the balancing, then hte bms is probably defective and should be replaced.

 

[qiubosu]

thanks for the information. the BMS only do the balance for the same parallel group cells, right? not balance between different parallel groups cells, right? i don't know whether the balance of the smart BMS used for this battery pack works well or not, as i haven't tried this functionality yet, and I haven't fully charged the whole battery pack with this smart BMS yet, while just working on the Bluetooth mobile Apps software at the moment. i think the balance of this smart BMS should work well. i used the simple charge i modified to bring the voltage of one particular parallel group cells to that closed to the other parallel groups of cells isn't for balancing, while just make the voltage more consistent, as consistency is the requirement for the smart BMS to function well to its potential. am i correct?

 

[amberwolf]

thanks for the information. the BMS only do the balance for the same parallel group cells, right? not balance between different parallel groups cells, right?

a bms must balance the entire pack such that all cells end up fully charged to the hvc point the bms is designed around. if it's progammable, then to whatever hvc point it's set to.

so if it's made for 4.2v per cell, then all cells will end up at 4.2v when balancing is complete.

whether or not this actually occurs precisely depends on the cells themselves, the wiring from the cells to the bms (balance / sense wires), any connectors between the cells and bms, and the bms's own voltage detectors / measurement accuracy. the closer to equal all the channels are in characteristics, the closer the final balance will be. with a crappy bms, you might end up with as much as several hundredths of a volt to a tenth of a volt difference. with the common ones, it might be a hundredth or few diferent between different groups.


so...within a parallel group, all cells are 'balanced' by the actual parallel connection. no bms is needed to do this part, they're forced to be equal voltage simply by being in parallel.

between different parallel groups, balancing is the job of the bms, if it has a balancing function, which most generic ones do. it just does it automatically by it's design in the case of a discrete-component type, and by whatever software settings it has in the case of programmable ones.

as consistency is the requirement for the smart BMS to function well to its potential.

the bms should make the pack consistent on it's own. if it does not, then it's not working.

if there is a large difference in state of charge between groups, it will just take that much longer for it to do it...but it should be capable of it.

it doesn't hurt to help it along, and a pack should actually come to you balanced already when ti's new, regardless of it's state of charge.


fwiw cell groups that are not in balance to begin with mean there is something wrong with the pack to start with.

either a channel in the bms is stuck on and draining cells continously, or a cell in a parallel group of cells is electrically leaky and draining all the other cells paralleled to it.

if either of those is happening, then after you manually charge that group to match the others, and then just let the pack sit for a week or so, it'll probably be low again if either of those is happening. it may take longer than a week if the drain is low, especially at the center of the state of charge region, the flat part of the curve, which is uusally around 3.7-3.8v for a lot fo common 18650 cells, to show the voltage difference. it's easier to quickly see at the top or bottom of the curve / voltage range.


it's also possible the pack builder simply didn't bother pre-balancing the cells when building the pack, or built the cell groups at different times from different batches of cells, so some had more charge than others, and the low group just started out low because it didn't have as much charge, etc. in that case, nothing is actualy wrong except a careless pack builder, indicating a close examination of all othe rpack characteristics is in order, because who knows what else they forgot or didn't bother wiht.

 

[qiubosu]

thank you so much for the information to share your experience.

after i built the new battery packs with BMS (not smart, but with balancing) installed, i left the pack charged for about one day, and when the charger light changed from red to green, i stopped the charging, but sometimes (some packs, as i built a few packs), the voltage of different parallel groups are quite different from each other, e.g. one group is 4.20v and the other group is 4.16v. i don't know whether the balancing feature doesn't work well, or i should left the packs being charged for longer period, when the charger light already became green. maybe if i leave the packs charged for a few more days after the charger light is already green, then the packs can be eventually balanced.

i first time to install a smart BMS to the battery pack, and haven't charged the pack for longer enough time, and don't know whether the balancing feature work or not.

yes, you're right, if the balancing feature work, all the cells in the pack should be balanced eventually.

just don't know normally how long the newly built battery pack should be charged with a BMS with balancing feature.

 

[amberwolf]

after i built the new battery packs with BMS (not smart, but with balancing) installed, i left the pack charged for about one day, and when the charger light changed from red to green, i stopped the charging, but sometimes (some packs, as i built a few packs), the voltage of different parallel groups are quite different from each other, e.g. one group is 4.20v and the other group is 4.16v. i don't know whether the balancing feature doesn't work well, or i should left the packs being charged for longer period, when the charger light already became green. maybe if i leave the packs charged for a few more days after the charger light is already green, then the packs can be eventually balanced.

sometimes a charger light goes green when it completely shuts off, sometiems it means it' s in balancing mode with a tiny current still flowing. you'd have to either meausre the current, or you'd ahve to see what the charger instructions or specs say, if anything.

but somtimes it's just that teh bms has shut off due to a high cell, and it has to drain that cell down and then ti'll resstart charging. if theres a significant difference, the process can take hours to days, because most bms have very tiny balancing current abilty. if there s a realy big difference, it can take weeks.

some bms just suck and dont' work right, too.



however....note that if you build packs from mismatched cells, then balancing will never be perfect, nor will it hold if you use the packs hard or drain them down very far.

if tehy're matched cells, then they should be balanced pretty well to start with, so the process on first charge shouldn't take too long, and they shoudlnt' need balancing very often or very much when they do.

 

[qiubosu]

yes, you're right. i can try to charge the packs for longer period to see the difference. i purchased a few hundreds brand new 18650 cells about half year ago, and just started to assemble them one month ago. the cells should be quite matched with each other, just a few of them slightly not matched. i added external connector, similar as BMS balance connector, to each pack i built, so i can externally measure each parallel group voltage with multi-meter. i think i can leave the packs being charged for longer period when the charger light becomes green, and via the external connector, to measure the voltage of each group to see whether there is any voltage increase when the charger light is in green for long, then i can tell whether the BMS balance working or not.

so far i built a few packs with almost all the brand new cells, and the whole process is quite good in my opinion.

 

[qiubosu]

i played around and the bluetooth apps of the smart BMS work on both of my Android mobile and tablet now. can update some parameters, but some parameters calculated from these updated parameters are incorrect, but in my opinion, this may not really affect how the charge & discharge work correctly (however it is good to make the calculations correct). the balance (both static and charge balance) works quite well and this is very important. the odd & even number series of cells are balanced in turn, which is good. with this Android mobile apps, some important parameters can't be adjusted, e.g. temperature sensors control parameters. some other parameters should be able to be adjusted also, e.g. hardware over & under voltage protection, charge overcurrent etc. for balance, it seems only can do balance when charge, but not when discharge, which is very important.

don't have the UART module to run on PC, and PC module software may be able to update more parameters.

anyway the smart BMS hardware and the Android mobile apps do work and do worth the money. this is my current findings of this smart BMS system when installed it onto the large 18650 Lithium battery pack I just built a few days ago.