36V 10S2P pack not charging - bad cells or BMS?

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lineslim

1 mW
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Apr 30, 2019
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Hi,

I got a hoverboard for free from a friend because it would not power on or charge at all (no red light on charger). I measured the battery voltage to be 17V (a 36V 10S2P pack with Samsung cells, see pictures). After opening the battery pack I tried to charge it by connecting the charger directly to the B+ and B- on the BMS (for short periods monitoring the voltage and temperature regularly). When reaching around 32-35V I was able to power on/off the board. Foot sensors seemed to work but it kept displaying a red battery symbol and beeping to signal low battery. Still it would not charge "the normal way" through the charge port. Shorting between C- and B- (as I saw in a youtube video) starts the charging but it cuts out as soon as the short is removed. I have also tried to "reset the battery" according to the manual by swiching the board on/of at certain intervals,

From what I have learnt this is likely a case of either a dead BMS or bad cells in the pack? Is there any way I could determine which of these it might be without taking all the cells apart? Or is there another way of trying fixing this problem before I go and buy a new battery?

Would really appreciate your advice!
 

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Start at neg. end and check cell voltage like.
1. 3.99v
2. 4.12v
3. 4.18v


10. Xxx volt
Best to write down on paper so you can ez see. Progress
Check charger voltage.
 
Thanks for the reply.

Charger output is 41.7V. I hope I managed to measure the cells correctly, at least they almost add up to 30V which I get between B+ and B-:
1)0.2V
2)3.6V
3)4.3V
4)4.3V
5)0.0V
6)1.6V
7)3.9V
8)3.6V
9)4.1V
10)4.1V
I guess this means the battery cant be saved? Or is there a way to wake up those low voltage cells?
 
Looks like you have some bad cells. The Samsung 22p has a low voltage cutoff of 2.75v (Check out the snip from the data sheet.)


Looks like you have to take it apart if you want to try and repair it. It would be a lot of work for a used battery that may have a bad bms anyway. Mixing new cells with old cells isn't the best idea. If you can find a similar board that has the same problem as yours and you can find it cheep you might be able to scavenge usable cells from it.

If it were me, I would just put a new battery pack into it unless it is more cost effective to get a new board.

:D :bolt:
 
I agree bad cells. When they get that low, almost zero volts, it's sure to be a fire hazard if you try to bring them back. And when charging without the BMS, you've also got two groups of cells at the high limit.

A couple of years ago ebay seller alarmhookup was selling similar packs and they turned out to be mostly good, at least for me and a few other. He's found some more for sale, although his price is higher. On the other hand, you may prefer packs that are shrink wrapped. These are bare.

https://www.ebay.com/itm/SAMSUNG-36V-4-4AH-LITHIUM-ION-REPLACEMENT-BATTERY-6-5-8-10-EBIKE/183770566448?hash=item2ac9944f30:g:qgIAAOSwcgNZArTx:sc:FedExHomeDelivery!60565!US!-1
 
You are probably right. A new spare battery is only about the equivalent of $53 from the store that sold the board, i.e. a better chance to get good quality than on ebay or aliexpress where they are about the same when you add customs & shipping fee + VAT.
Thanks for your advice!

-> docw009: Thanks for the link. If there was a seller within the EU that would be a good price for me, from outside EU a "VAT collection fee" of $8 and 25% VAT on top of it all is added automatically on all shipments to Sweden unfortunately :-(
 
Cells 1, 5,6. Are garbage and can not be recharged. Fire hazard. You may check other as 2p each group if you have rc chager a hassle and hard for me to tell to make you a battery mad scientist.
 
On second thoughts, I got an ide that may not work but:

Could I make a 10S1P pack out of the good cells and still use the same BMS board? It would have half the capacity but enough to test the hoverboard to see if everything works well before purchasing a new battery. Besides, it would be fun if it would work :). It does n't seem that complicated to remove one cell in each pair and insert three of the removed good ones instead of the three bad pairs?

Second question: Could the BMS handle a mix of cell groups consisting of either one or two cells as long as they add up to 10 groups in series? i.e. could I leave 2 cells in one or two of the groups if they are not needed to replace the bad groups?
 
lineslim said:
On second thoughts, I got an ide that may not work but:

Could I make a 10S1P pack out of the good cells and still use the same BMS board? It would have half the capacity but enough to test the hoverboard to see if everything works well before purchasing a new battery. Besides, it would be fun if it would work :). It does n't seem that complicated to remove one cell in each pair and insert three of the removed good ones instead of the three bad pairs?

Second question: Could the BMS handle a mix of cell groups consisting of either one or two cells as long as they add up to 10 groups in series? i.e. could I leave 2 cells in one or two of the groups if they are not needed to replace the bad groups?
Click to expand...

It's certainly possible to reconfigure the pack to 10S but with half capacity. But you may find that it won't be able to give enough power without voltage drop or overheating. Preferably you would spot weld the cells in the new configuration but you may be able to get away with soldering if you leave the nickel strips on.

While it will work to have different numbers of parallel cells in each series cell group, the series cell groups could become unbalanced during use or charging which will limit total usable capacity or cause longer charging times. It will also put more load on certain series cell groups which could accelerate their aging.
 
Get a marker and write on the cells the voltage and maybe just leave him in Paris you could figure it out. Put the ones lower than 2.8v or 3.0v in a bucket of water and salt. If you eant to see sometime cells water then salt.
Sorry 2.8v not 28v
 
Making a 1p pack might tell you what is working, but if that motor pulls more then 10 amps then the cells will not be able to handle it. It could however answer the BMS question. Just don't ride it if the batteries get hot.

:D :bolt:
 
Its the BMS. I just had to take apart and replace that EXACT BMS in an identical 36V hoverboard battery. I bought 11 of those batteries and the only 2 that failed (wouldnt charge) on me were the 2 that had that BMS. Im pretty sure thats the one that got hoverboards banned everywhere.
 
aw, crap. I just got 2 discarded dell laptop batteries from IT to salvage cells from. But if also the BMS is toast Im back to square one.. I will test anyway to replace the bad cells tonight. I checked with the store chain that sold the hoverboard but the serial was not on their list of recalls for this product (Due to fire hazard from the battery)
 
Computer batteries are not usually high C batteries and will probably get hot during usage. How much does a replacement 36v battery pack cost? $60.00 USA?

If you want the experience of rebuilding a battery pack, then go for it, however if you find that the bms is good, there are much better cells on the market then the ones in your battery.

:D :bolt:
 
I opened the computer battery and found 3 pairs of samsung 18650-30 something (cant remember exactly). All of the cells were about 3.8V so I swapped out the three bad pairs in my pack. Assembled and measured 39.xV. Put it in the howerboard and it works just fine :). Dont know how long it will last though. Connected the 42V charger but still only the green light, guess the BMS is bad afterall. Or shouldn't charging start until voltage has dropped further? The battery indicator on the hoverboard itself is still green so It doesn't signal that it wants to be charged.
 
999zip999 said:
Those samsung cells look good 35.00 plus 12 shipping. 5 posts from the top of thread.
Click to expand...
I would assume that "new" pack comprises used or QA "B" cells
 
I was looking on eBay at 36v replacement batteries. I can not vouch for quality. Watch that the battery doesn't go below 27v. If it does then you know that the bms is not cutting off the discharge soon enough for the original cells. If you want to rebuild your pack entirely, a place like Nkon has genuine cells. Something like Sony 18650VTC5A 2600mAh - 35A or the Panasonic NCR18650BD 3200mAh - 10A would be far superior to the original batteries. Your original batteries are also on sale at Nkon for about $1.50 USA, each, but are 3 years old. Fresh is better when it come to li-ion cells.

:D :bolt:
 
lineslim said:
I opened the computer battery and found 3 pairs of samsung 18650-30 something (cant remember exactly). .....
Click to expand...

Good that you found real Samsung's. But that part of the number you can't remember important. It tells the type of charge, discharge, and continuous discharge characteristics you need to know. Look again and post the full number.

:D :bolt:
 
e-beach said:
a place like Nkon has genuine cells. Something like Sony 18650VTC5A 2600mAh - 35A or the Panasonic NCR18650BD 3200mAh - 10A would be far superior
Click to expand...
Not to derail but quality models and

trusted **suppliers** for A-quality 26650 size would also be appreciated

for both LFP (A123, maybe K2?) and the other LI chemistries

would be greatly appreciated

Are there other larger-capacity sizes actually available at reasonable cost per Ah?


 
john61ct said:
...... but quality models and trusted **suppliers** for A-quality 26650 size would also be appreciated for both LFP (A123, maybe K2?) and the other LI chemistries would be greatly appreciated Are there other larger-capacity sizes actually available at reasonable cost per Ah?
Click to expand...

Check out the Nkon and Nkon.ru website and tell me what you think.

:D :bolt:
 
Thanks! Seems this is the only LFP they sell

https://www.imrbatteries.com/a123-systems-anr26650-2500mah-flat-top-battery/

Rather than divert this thread, everyone please post any more such suggestions here

https://endless-sphere.com/forums/viewtopic.php?t=99991
 
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