Help I need to identify this BMS ..i have no clue where to start but a lot of questions.

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samsungante

New member
Joined
Feb 25, 2021
Messages
1
Basically, I am doing a small portable battery bank out of thesee hoverboard batteries (110Wh) for my school project.
But in my paper I should describe basic principle of operation of every component. I have no clue in power electronics and im stuck at BMS description,
All i know is that there is 7 controlers for every series part.
I see 4 MOSFETS and RS3M diode that connects B7 and P- section. Is there any short circuit protection ?
Please if anybody can regognize anything more in detail on this PCB be welcome to comment.
I have no idea is this 10A or 15A. :(
is there any balancing implemented ? i mean there could be even if there is no resistors for charge bleed, maybe some other type ?
 

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Roland W

Member
Joined
Oct 9, 2017
Messages
137
Basically, I am doing a small portable battery bank out of thesee hoverboard batteries (110Wh) for my school project.
But in my paper I should describe basic principle of operation of every component. I have no clue in power electronics and im stuck at BMS description,
All i know is that there is 7 controlers for every series part.
I see 4 MOSFETS and RS3M diode that connects B7 and P- section. Is there any short circuit protection ?
Please if anybody can regognize anything more in detail on this PCB be welcome to comment.
I have no idea is this 10A or 15A. :(
is there any balancing implemented ? i mean there could be even if there is no resistors for charge bleed, maybe some other type ?

Its a 7S BMS, 24V LiIon probably. If it would be for LiFePo, it would be an 8S. But you know that for sure when you charge the first time and see if the BMS is cutting out at 3.65 or 4.2V.
B- is the pad connecting to your battery main Minus
P- is the Load Minus
B1 is the the first balance lead to the first cell +
B2 the next cell +
etc....
It is resistive balancing, probably somewhere around 30mA looking at the small SMD resistors (see the row of 101 marked resistors on right top? Those are 100 ohms bleed resistors. 3,7V/100=37mA)
The Mosfets can theoretically switch 80A each, but they must be oversized by at least the factor of 6, so by the number of Mosfets I would put the max current somewhere to 30A, maybe 40A, but you would need to have a heatsink over those Fets.
 
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ajw22

Member
Joined
Nov 16, 2018
Messages
641
If you look at the datasheet for DW01 chip, it'll explain all the small components on the right side (DW01, 101, 2L , 824).

It is resistive balancing, probably somewhere around 30mA looking at the small SMD resistors
Perhaps there is a balancing mechanism on the reverse side, but as far as I can see it's not on this side. At an assumed 30~50mA, it would be an 84~140Ohm resistor. The 101 resistors (100Ohm) would be the right value, but they're most likely part of the required circuit to power the DW01
chip as suggested on page 3 "Typical Application circuit" in the datasheet. The orange SMD below the 101 resistors are therefore most likely 0.1uF capacitors.

Basically, the 7x DW01 chips check the cell voltages for over-charge / over-discharge.
Each DW01 has control over 2x "2L" transistors, with each being connected via a 824 resistor to
one (two?) common fault signal line(s). Thus any DW01 can pull-up (down?) the fault signal.
Note the 105 (1MOhm) resistors between the DW01 and 2L transistors. They will delay the switching of the transistors, so that brief voltage sags/spikes do not immediately trip the BMS.
I assumed the "2L"s are FETs, but looks like they are PNP transistors. So it might not be delay switching, but to just limit the current they can conduct.


The common fault signal line(s) probably indirectly control the main MOSFETs to stop charging or discharging.
Note that MOSFETs can only stop current flowing in one direction. It's not capable of stopping current flowing in the other direction (indicated by the diode in schematics). Thus 2 MOSFETs are connected head-to-head, one for stopping charging, and the other for stopping discharging.

The two big R010 are likely the shunts for over-current sensing. Two 0.01Ohms in parallel, so effectively 5mOhm.
The small island of resistors and transistors (G1, 224, 225, etc) must be the circuit to detect and shut off the MOSFETs in case of overcurrent/short circuit.

Not quite sure that the RS3M diode is for. Perhaps something to protect the ICs from reverse voltage.
 
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