Battery not charging at all anymore

Freshblood

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My battery use to work and charge properly for about 50 charges over the last year. I have done about 1200kms on this battery so it has done well. Then at some stage I realized I only got half the power out of the battery and then progressively down to about 25% within a couple of charges. I did not understand as the charger would automatically switch off when full charge is reached. I proceeded to check battery at full charge and it only showed 47.9V and it should be 54.8V.
That said, I checked each cell and found that some was 4.2V some 3.8V some 3.6 and so on. All over the place. I believed the BMS blew so I bought a new one. I installed but the charger does not want to charge the battery now at all. It guess it still see one of the cells at 4.2V so does not want to engage. How to now charge this battery if it does not even want to start? I checked the charger is still providing 54.8V of potential.
Thanks
 

Nealh

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0.6v is far out for the bms to balance, you need to partial discharge the high cells.
Either directly or indirectly via the bms wire connector you need to attach a 12v lamp or two to discharge the cells down to about 3.8v, monitoring the voltage. Then reconnect and try a charge it may not balance with the first charge.
 
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Andy-Mat

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My battery use to work and charge properly for about 50 charges over the last year. I have done about 1200kms on this battery so it has done well. Then at some stage I realized I only got half the power out of the battery and then progressively down to about 25% within a couple of charges. I did not understand as the charger would automatically switch off when full charge is reached. I proceeded to check battery at full charge and it only showed 47.9V and it should be 54.8V.
That said, I checked each cell and found that some was 4.2V some 3.8V some 3.6 and so on. All over the place. I believed the BMS blew so I bought a new one. I installed but the charger does not want to charge the battery now at all. It guess it still see one of the cells at 4.2V so does not want to engage. How to now charge this battery if it does not even want to start? I checked the charger is still providing 54.8V of potential.
Thanks
That sounds like possibly that the new BMS is in some manner incorrectly connected to the cells. This is (according to others) rather too easy to accidentally do....The main reason being that there two basic "methods" of connecting, both correct, but apparently looking to be the complete opposite of each other.....
But I also get the impression that the battery might need to be examined and charged, one block of "same" potential of cells at a time.....any block of cells at less than 4.2 volts to be charged, to check if some cells are already defective...
**** job, not without some personal danger....
regards
Andy
regards
Andy
 

vfr400

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Yes, there are several different arrangements for connecting the BMS sense wires. The BMS should be marked B0, B1, B2,B3, etc. You must measure the voltage at each of those points to the cell-pack's ground when connected. Make sure B0 is zero volts, B1 is approx 4v and so on all the way to B13.

Some BMSs don't have B0 or B13. They sense those from the ground or the positive cell-pack wire, but you should still expect the others to be right, i.e. B4 should be around 16V.

I've bought a replacement BMS that had the right connector on it, but the wires were completely reversed so B1 would have got connected to B12, etc.

Connectors can be in either direction and go B0 to B13 (14 pin), B0 to B12 (13 pin), B1 to B13 (13 pin)and B1 to B12 (12 pin), so two possibilities for 14 pin, four possibilities for 13 pin and two for 12 pin, so when you buy a BMS, you have to check which of the eight it is to match your connector, otherwise you'll need to rewire the sense wires.

If all that checks out, you have to balance your cells manually
 
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Nealh

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With bms I always confirm which is B0 or B- before even considering soldering them on, always leave the main jst sense connector dis-connected, If you have a Black wire and all other Red then the Black is B0. Once I have soldered all wires I then double check the connector voltage of each pin and the V's rise in ascending order only then do I connect to the bms it self. At any stage before final connection a mistake can be simply rectified.


For balancing it is often only one or two cell groups that are high and I have found it easier to discharge one or two rather then raising several groups which is more time consuming. Once all cell groups are at similar level then refit the balance connector and charge the battery up whilst still in an undressed state to confirm all is well, once all is well redress the battery.
Better to to check before redressing to save wasted time undoing again.
 
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Andy-Mat

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Some really good recent posts here on the subject of BMS connections and the possible errors.
It is not as simple as some think it is......
There are some good links on re-building of batteries on the IoT, but its still possible to accidentally screw up!
regards
Andy
 

Nealh

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Before anyone starts thinking about bms wire connections and think swapping one out is simple, it is best to sit down and understand how volts flow through a battery pack and how they are inter connected to follow the flow path as it passes through the pack from one end to the other.

Starting at 0v or B- the need to know how to measure check the next voltage is quite basic but necessary to avoid mistakes, once the workings/voltage path is understood then the process is easy to understand. Next is the ability to be able to solder good contact connections.
Also safety when working with batteries is required, shorting cells can easily happen with a misplaced metallic object.
 

Andy-Mat

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Oct 26, 2018
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Before anyone starts thinking about bms wire connections and think swapping one out is simple, it is best to sit down and understand how volts flow through a battery pack and how they are inter connected to follow the flow path as it passes through the pack from one end to the other.

Starting at 0v or B- the need to know how to measure check the next voltage is quite basic but necessary to avoid mistakes, once the workings/voltage path is understood then the process is easy to understand. Next is the ability to be able to solder good contact connections.
Also safety when working with batteries is required, shorting cells can easily happen with a misplaced metallic object.
A really good post that I fully agree with, in spite of the fact that a lot of my e-bike battery knowledge only comes from reading some good websites on the subject, and even though I am a electrical engineer of many years experience, I know when its a good idea to play safe!
Though about 5 years ago I had to replace the BMS on my previous bike's battery, but that was made really simple by replacing with exactly the same one - "easy peasy" as the kids would say......
I hope I never ever need to replace original with only "similar"....
On my present bike, I have not needed to open up either of my batteries as they are relatively new and probably still under guarantee, both are filled with quality cells from Panasonic!.
Lets hope that it stays that way!!
regards
Andy
 

Freshblood

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Thanks for all the replies. Let's assume I soldered these points correctly and in the correct order, it might be that the range of balancing is out of wack and cannot normalize. The reason I am saying this is due to the fact that the previous BMS worked for 50 charges perfectly and then suddenly not. I resoldered the new BMS in the similar fashion. I discharged the battery today for the first time and charged again. The charger fired up and charged the pack up to 48.9V, switched off automatically and then leaked to 48V. So the same problem as before.
The cells are all still good (I believe) as the problem happened rather instantly.
Could some of the cell be too low to start charging at all? Like for example of the cell has dropped below 3.4V? It is a 13S4P battery by the way. The cell voltages are all over the place for example it would be S1=4.2, S2=3.8, S3=3.6, S4=4.2, S5=4, S6=4, S7=3.5, S8=3.6, S9=3.8, S10=3.8, S11=4.2, S12=4, S13=3.6.
 

Freshblood

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0.6v is far out for the bms to balance, you need to partial discharge the high cells.
Either directly or indirectly via the bms wire connector you need to attach a 12v lamp or two to discharge the cells down to about 3.8v, monitoring the voltage. Then reconnect and try a charge it may not balance with the first charge.
Thanks. I discharged the battery today down to auto switch-off. I proceeded to charge and the charger switched off automatically at 48.9V, which was the same as with previous BMS. The charger is pushing 54.8V(checked) So from complete discharge the BMS should be able to balance the charge. Is it possible that a discharged cell could be too low to be even considered in BMS??
 

vfr400

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The charger charges all ceells equally. If one cell group won't charge, none of them will. The BMS stops the charger as soon as the first reaches 4.2V and switches off discharge as soon as the first reaches 3.0V.

Your problem is that the pack is out of balance. The question is why? All you can do is balance them manually, then see what happens. If it goes out of balance again, you have faulty cells or some welds have broken.

It's easiest to drainthe high ones down. They're 4v approx, so you can use a 12v indicator bulb of around 15W, which shoult take around one amp at the lower voltage. Do not forget about it after you connected because it'll drain the cell group down to zero eventually. You need to stop at 3.6v..
 

Nealh

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The charger fired up and charged the pack up to 48.9V, switched off automatically and then leaked to 48V. So the same problem as before.
The cells are all still good (I believe) as the problem happened rather instantly.
Could some of the cell be too low to start charging at all? Like for example of the cell has dropped below 3.4V? It is a 13S4P battery by the way. The cell voltages are all over the place for example it would be S1=4.2, S2=3.8, S3=3.6, S4=4.2, S5=4, S6=4, S7=3.5, S8=3.6, S9=3.8, S10=3.8, S11=4.2, S12=4, S13=3.6.
Depending on the new BMS specs the max charge voltage may be 4.25v before the bleed discharge rectifies this, as you have 2 or 3 high cell groups thye likely went above 4.2v then later on bled back below 4.2v to give the reading you saw.
As said in other posts you will painstakingly have to manually discharge all high cell groups to the lower values, keeping an eye on the voltage as each group decreases. Once all are at 3.5/3.6v then try a full balance charge.
 

Nealh

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Knowledge reading via the internet on the subject can't be dismissed, this helps to bare fruit when you transfer that knowhow learnt in to real world practice on a battery in need of attention.
 

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