BMS not working?

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helpme

New member
Joined
Feb 2, 2021
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5
Hello, please help me, I made my own lithium-ion battery 4S35P 18650 with BMS. Everything is working. I tested the electric motor for 1 hour at 40 A, all cells had the same voltage, but when I discharged it with 2 A for 24 hours, 3 cells had a voltage of about 3.6 V, + -0.1-0.2 V , the last cell had 1.5V. why? Why doesn't it discharge evenly? After disconnecting the load, the voltage of the last article began to rise. I apologize for my English. Thank you for your response
 
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italianuser

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Joined
Feb 25, 2020
Messages
374
Does forum have an optional translate-link plugin? :unsure:

Because I speak all languages a part from greek... and this is greek to me LOL 😅
 

barry

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Joined
Oct 19, 2019
Messages
66
Hellou, prosím pomozte mi, vyrobil jsem si vlastní lithium-iontovou baterii 4S35P 18650 s BMS. Všechno funguje. Testoval jsem elektromotor po dobu 1 hodiny při 40 A, všechny články měly stejné napětí, ale když jsem jej vybil proudem 2 A po dobu 24 hodin, 3 články měly napětí asi 3,6 V, + -0,1-0,2 V, poslední buňka měla 1, 5V. proč? Proč se nevybíjí rovnoměrně? Po odpojení zátěže začalo napětí posledního článku stoupat .. Omlouvám se za mou angličtinu. Děkuji za Vaši odpověď

Hello, please help me, I made my own lithium-ion battery 4S35P 18650 with BMS. Everything is working. I tested the electric motor for 1 hour at 40 A, all cells had the same voltage, but when I discharged it with 2 A for 24 hours, 3 cells had a voltage of about 3.6 V, + -0.1-0.2 V , the last cell had 1.5V. why? Why doesn't it discharge evenly? After disconnecting the load, the voltage of the last article began to rise. I apologize for my English. Thank you for your response
 

barry

Member
Joined
Oct 19, 2019
Messages
66
1) your config of your BMS is incorrect the low voltage disconnect is not working!!
2) How did you build your packs? did you sort it by milli amp hours? and IR?
3) buy a good BMS... do not buy cheap fake sh#t for a few dollars..
 

helpme

New member
Joined
Feb 2, 2021
Messages
5
1) your config of your BMS is incorrect the low voltage disconnect is not working!!
2) How did you build your packs? did you sort it by milli amp hours? and IR?
3) buy a good BMS... do not buy cheap fake sh#t for a few dollars..
Yes. I sorted by mah .. and can you advise good bms? li-ion 4s 60A
 

helpme

New member
Joined
Feb 2, 2021
Messages
5
I don't understand why it only fired the last battery block. Battery block have 3.63V, 3.61V 3.61V and 2.89V... Where the LED light shines. I'm trying to replace the bms
 

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ajw22

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Joined
Nov 16, 2018
Messages
641
One issue I see is that the BMS seems to be configured for 3S operation, so it's probably not monitoring the first cell. Note the "Short" and "Hanging"(=open?) in the diagram. I think those need to be changed for the BMS to be in 4S mode.
EDIT: Also note the missing black box (a 0 Ohm jumper) right under the letters "B2"

Not a problem, but the balance/sensor wires can be much much thinner, since very little current flow through those.
EDIT: the misconfigured BMS may be drawing quite a bit of current on port "B2"

Pictures of the whole pack, including the back side and where the main (+) and (-) connect might help to spot more potential issues.
1612331479406.png
 
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ajw22

Member
Joined
Nov 16, 2018
Messages
641
[...] have 3.63V, 3.61V 3.61V and 2.89V...

Possible causes:
* Misconfigured BMS was draining the last module (Hard to say without analyzing the BMS, but I think this is most likely)
* Last module was not fully charged to begin with
* Last module has lower capacity cells (some cells may have died)
* Last module has self discharging cell(s)
* Bad wiring
 

helpme

New member
Joined
Feb 2, 2021
Messages
5
One issue I see is that the BMS seems to be configured for 3S operation, so it's probably not monitoring the first cell. Note the "Short" and "Hanging"(=open?) in the diagram. I think those need to be changed for the BMS to be in 4S mode.
Thanks for advice. In the evening I will change hanging - short. And I'll try. That will probably be the reason. Thank you
 
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