TonyVov

I am having problem with my battery.
Bafang HT1204DA 43V 450wH
The cells are Samsung ICR18650-26H 2600mAh (Pink)
Nominal Voltage: 3.63V per cell.

The pack should be 10ah and is delivering about 2-3ah following a deep discharge incident.
I cannot buy a new battery here. I have access to tools required to repair/rebuild. I can buy new cells.
I am trying to work out if I have a chicken or an egg??

The pack is open and I can measure down to cell level but the pins are very tiny.
I observe the battery stops charging at 44.3v and with load applied BMS cuts the power at 44.1
What I can't work out is if this is due to problem with cell, bms or charger.
Everything in this pack seems to be "smart" with battery talking to charger and controller.
However I cannot find anywhere instructions on how to "tak" to the BMS and see if it is still programmed correctly.

Can someone guide me with troubleshooting ideas??
How to talk to a battery through UART
How to check if it is cells or bms or charger.



here is the details of the battery specification:
43V Bafang Battery
BT C01.450.UART
12 C I R 18 65 4 10.4aH
HT1204DA 43V 450wH HiTech
Barcode BT C01 450 U A2R8290071
Batch mode CC-CV (Special 5P Charger)
Bus system UART

My summary:
12 series 4 parallel
12x3.63=43.56V 12x4=48cells
4x2.6aH=10.4ah x 43.56V = 453wH
Discharge max = 20A
Charge std 1.3x4= 5.2a Charge quick and Max = 2.6x4= 10.4A
Charge V = 12x4.2 = 50.4 A
Discharge cutoff 2.75V x 12 = 33V
Charge guesstimate
4.2V = 50V = 2600mahx4 = 10.4ah = 453Wh
3.9V = 47V = 1600mahx4= 6.4 ah = 279 Wh
3.62 = 43.4V = 1100mahx4 = 4.4 ah = 190 wh
3.56 = 42.7V = 600mah x 4 = 2.4ah = 104wh
3.4 = 40.8V = 100mah x 4 = 0.4ah = 17.4wh


Bafang 5P smart Charger
SSLC100V49
49.2V 2A
CHG C01 2A EN A1R7200243
Wuxi Sans Electronic

BMS
c
ht1205aa-bmu rev:1
8P043bmu1p02

Doc_Wui

I guess you have to find the bluetooth specs and the App, so you can hook your phone up to the battery and look at all 12 group voltages. Without that, you have to measure them with your meter. Yes, the wires are tiny, but you could remove some of the wrapping and probe the backs of the cells. Or you pull the BMS balance wire connector, if it has one. and measure there. Be careful and don't short ciruit the cells.

You need those volatges to tell what's going on. If it is working properly, the BMS will shut down the charging because one or more of the 12 groups is at 4.2V. You need to know what the voltages are on the other groups.

TonyVov

Doc_Lui thanks for the feedback.
I didn't think about blue tooth.

I will have to open the pack and get at the back of each cell with a wire, it is too dangerous to try to measure at the balance connector.

The pack design inside the case makes this thing wobbly like a snake on accessing the lower cells with case removed, a bit risky to play with.
I'll add extra wires and reassemble to test.

I turned on the battery and hunted for any available BT device around the BMS , no luck.

There are two unused connectors on the top of the bms maybe one is for comms.

I will test drain the battery with connector on and then off.


I tried to Post photo but don't have enough points.

It is hard to work without documentation.
Does Bafang not have manuals somewhere?

chas58

Do you have a digital multimeter? Can you measure the voltage of both the charge and the discharge leads? If the voltage is within 30V to 42V on both charge and discharge leads can you connect the battery to your kit and then measure the voltage to see if there is a significant voltage drop? If the voltage is lower than 30V or if there is a significant voltage drop this likely points to either an issue with the BMS or an issue with the cell groups. To determine this you will need to access the balance header connector that goes to the BMS and measure the cell group voltages.

measure:
Charger output voltage. is this appropriate?
Voltage of each series group of cells after a full charge, 1-?V, 2-?V, 3-?V Etc. (Do not measure everything back to the pack negative, measure to adjacent pins). A fully charged LiPo, NCM, Li Ion cell, will have a voltage >4.15V.
If all cell groups are not fully charged, try to charge the low cells if at all possible.
Voltage of each series group of cells after a full discharge (after BMS has tripped), 1-?V, 2-?V, 3-?V Etc. A Li Ion BMS will trip when any cell hits 2.75V. Cells do bounce back up to a higher voltage after the load has been removed.


If every cell group in the pack is not fully charged (>4.15V for NCM/NCA ), then steps should be taken to manually charge any low cell groups. This can be done by charging the low cell groups at a low charge rate, through the BMS balance lead. Charge current should be limited to ~0.2A, as there are PPTC thermal fuses on the BMS Balance wires to the battery. Charging can be done using an RC Type charger, or any type of suitable device, that can charge to the required voltage.

TonyVov

Chas58 thanks for the helpful advice, I attached a zipped xl file to original post with some charge discharge data.

My current plan-
-Stick some wires on each group. Needs disassembly and reassembly.
- stick some wires into the charger connector so I can see the output of charger.
-Ty to get all cells to same voltage and close to 4.2V either by individual group charge or discharge. Limiting charge to 0.2a
- try to get repeated info on discharge shutdown BEFORE shutoff and see if any one group drops to 2.75V, so far minimum seen is 3.2V but this could be bounce back.
- manually discharge without bms connected monitoring cell voltages

Bafang 5P smart Charger
SSLC100V49
49.2V 2A
Max voltage seen is 44-45V
This smart charger will not even turn on if it is not connected to bms.
During discharge the bms did off at about 42V right now.

I have DVM with DC clamp ammeter.
I have a 25ohm 2500w dump resistor as load cell.
I will try to get access to lab power supply with voltage and current supply.

Many thanks

TonyV

Doc_Wui

Only some batteries have blue tooth BMS, My fault. With all those specs you were tossing at us, I thought I saw bluetooth in there,

If you have some electrical skills and understand how cells are connected in series, it's not hard to walk a pair of probes up the ends of the cells and map out the voltages. And sometimes, everything is there at the balance connector.

Some people have no idea on how to do this, so they shouldn't even try. It's best to be very respectful if not afraid of the energy/power inside an ebike battery.

chas58

Technically, you can measure the battery voltage off the BMS.

After removing the battery from the charger, remove the multi-pin BMS Balance plug from the BMS and measure the voltage on the adjacent pins (pins 1-2, 3-4, 4-5, etc.) in the plug, with pin 1 being the single black cable. DO NOT measure everything back to the black wire, you must measure the voltage, between adjacent pins. The voltages should be something like 3.6, 3.56, 3.62, 3.59 etc… A fully charged LiPo, NCM, Li Ion cell, will have a voltage >4.15V. We are looking for any cells that are significantly higher or lower than the others in the pack.

TonyVov

Thanks for the advice.
My BMS balance connector is very tiny I don't have the probes to go pint pin safely.

I dismounted the cells to add a wire to reach group separately, my Bafang 12sx4p pack has 4 "pockets" with 3 groups in each pocket.

The group number 9 is now short circuit, 0.2 V with BMS connector on and off.
Other cells vary from 4.2V to 3.6V.

This was not the case last week. I am praying I am looking at the cause.

Looks like I am going to have to replace my cells.

I'll update this case later after I have new cells installed.


Hopefully I will get my 10 posts in soon and can post some real photos to this forum.

chas58

one more post to go!