BMS 1 cell low voltage

vadikb

1 mW
Joined
Oct 15, 2012
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14
Location
Osaka, Japan
I have 36v 15Ah battery pack. All of a sudden the LCD doesn't turn on. Batteries wont charge. Charger shows green light when connected. Charging port shows exactly 36v and voltage directly from batteries port +- shows 37v. The app and the multimeter shows exactly same data and low voltage in cell 3.

Is there a way to fix this without taking all the batteries out of cell 3?

Battery pack 4P10S 36v
BMS MGod 10S 36V 30A
 

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If group 3 is really nearly zero volts, those cells are toast, and are why the BMS will not allow charge; its' trying to prevent a battery fire.

If you open the pack and find that those four cells really are that low, you can replace them with new ones.

What brand and model cells are they? Knowing that will help you find replacements.

Was the pack bought prebuilt, or is it DIY? (if the latter, then you probably already have the tools to repair it; if the former it might be cheaper to have someone else do the work than to buy the tools to repair it and spend the time and materials to learn to use them).

Have the cells in that group been getting lower and lower all the time, or was this a sudden "instantaneous" event?

If the former, the BMS might have a stuck-on balancer (if it even has a balancing function, not all of them do), and that might have drained the group empty. If so, it will do the same thing to whatever you replace them with.

If the latter, a cell in the group might have internally failed and drained the others; if so then once all four are replaced it won't matter, as the bad one will be gone.

Another possibility is a pinched balance wire, shorted to another cell, etc.; this could also drain new cells.
 
Could this be same 10S4P DIY battery kit you built in 2013 ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=56112&p=835886#p835886 ?
vadikb said:
Hi. My 36v 9ah tube battery was stolen, and now I am in need to make another one. For my little project I will be getting this set: http://www.aliexpress.com/item/Water-bottle-type-e-bike-battery-box-Used-for-18650-cell-assembly-With-free-cell-holder/1565979743.html
Is this the same 2013 DIY battery now with #3 at 0.248V? If so it's likely time for a new DIY build using all new cells.
 
amberwolf said:
Have the cells in that group been getting lower and lower all the time, or was this a sudden "instantaneous" event?

If the former, the BMS might have a stuck-on balancer (if it even has a balancing function, not all of them do), and that might have drained the group empty. If so, it will do the same thing to whatever you replace them with.

Yeah this happened suddenly after a year of use. If the BMS stuck on balancer, will connecting a new smart BMS balance the batteries automatically or do I still need to get those batteries out of that group and charge them manually to match the voltage with other groups? :eek:
 
eMark said:
Is this the same 2013 DIY battery now with #3 at 0.248V? If so it's likely time for a new DIY build using all new cells.

This is my 50th pack so far, using a smart BMS for the first time. Never had exact issue with my other builds so I am kind of hoping it is it the BMS and not the problem with the cell(s). Replacing the cells is a very tedious task.. :?
 
vadikb said:
Yeah this happened suddenly after a year of use. If the BMS stuck on balancer, will connecting a new smart BMS balance the batteries automatically or do I still need to get those batteries out of that group and charge them manually to match the voltage with other groups? :eek:

Neither. They are damaged and a fire risk. You need to replace them.

If you don't, you can't predict what will happen or when, and they may burst into flame at any moment once recharged, either during charge, during use, or even just sitting there.

They may, of course, do nothing other than perform much worse than they originally did, lowering the capacity and performance of the pack, but I would think that any risk of fire would be unacceptable.

If it's not unacceptable to you and you intend to recharge the cells, then please make sure you never use or store the pack anywhere near other people or animals who may be injured or killed if it does burst into flame.


If you can see the balancing resistors and transistors on the BMS board (some are covered in goop and essentially untestable), then you can test the BMS for leakage at the balance wire by disconnecting the balance wire from that cell group (or just unplug the entire balance connector from the cells).

Find the balance resistor that leads to that wire. There will then be a transistor with one of it's leads connected to the other end of that resistor. That lead you don't test; it would just read the reisstance of the balancer, which is unimportant.

Then set your multimeter to 2kohms. Place the black meter lead on the disconnected end of that balance wire, and the red meter lead on one of the other two leads of the transistor of that balancer. It should read "open circuit". If it reads anything else, go to the next lead of that transistor. It should read open circuit.

If you get a reading on either one that is essentially the same as the balancer resistor's resistance, it means that transistor is stuck on, and you need a new BMS and new cells.

If it reads open circuit, it's not stuck on, and you probably don't need a new BMS, just new cells.







Example of the kind of parts arrangement you're looking for is below; every BMS is a little different.

Bleeding-balancing-BMS.JPG
 
amberwolf said:
vadikb said:
Yeah this happened suddenly after a year of use. If the BMS stuck on balancer, will connecting a new smart BMS balance the batteries automatically or do I still need to get those batteries out of that group and charge them manually to match the voltage with other groups? :eek:

Neither. They are damaged and a fire risk. You need to replace them.

I wasn't able to open the BMS so I removed the batteries instead and tried to charge them but without avail. I am still confused to why all 4 cells are drained to such low voltage. It can't be that all 4 cells just simply died all of a sudden, right? Is there any way to revive any of the cells? Even if it is possible would it be safer to replace those dead cells anyways?
 

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vadikb said:
amberwolf said:
vadikb said:
Yeah this happened suddenly after a year of use. If the BMS stuck on balancer, will connecting a new smart BMS balance the batteries automatically or do I still need to get those batteries out of that group and charge them manually to match the voltage with other groups? :eek:

Neither. They are damaged and a :flame: :flame: fire risk :flame: :flame: . You need to replace them.

I wasn't able to open the BMS so I removed the batteries instead and tried to charge them but without avail. I am still confused to why all 4 cells are drained to such low voltage. It can't be that all 4 cells just simply died all of a sudden, right? Is there any way to revive any of the cells? Even if it is possible would it be safer to replace those dead cells anyways?
As I noted before:

They are damaged and a :flame: :flame: fire risk :flame: :flame:.


If you're going to recharge them anyway, PLEASE keep them and any battery they are part of, whether in use or not, charging or discharging or just sitting there, away from any other living beings so you don't kill them in the fire they could cause. Risking your own life and property is your choice, but if you are in a shared dwelling or near others, don't use or keep them there.
 
amberwolf said:
They are damaged and a :flame: :flame: fire risk :flame: :flame:.

Yes I am aware of the fire hazard when dealing with batteries. I have a large metal storage container where I assemble, troubleshoot and charge these batteries :bigthumb:
I wont be using these damaged cells in any pack but I am curious if it is possible to bring them back to full voltage for more testing. My current charger stops charging the cells at around 1.5v.
 
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