Daly BMS 24V 8S 100A - poor balancing + charging and discharging prematurely stopped

[Marten]

A random battery cell of 8 pieces stops charging and discharging when it hits the highest or lowest point. (Daly BMS doesn't balance right)


Daly BMS 24V 8S 100A (R16A-GA14) Software version/Firmware: 20201205-1.01G

(sorry for my poor English)

Charging:
Once one cell hits 3.65V, then the Daly BMS stops charging. Balancing is also stopped. The other 7 cells have: 3,451 . 3,454 . 3,398 . 3,389 . 3,399 . 3,395, 3,401

7 battery cells have low voltage :-(

Discharge:

Once one cell hits 2.5V then Daly BMS stops discharging. The other 7 cells have: 2.864 . 2,902. 2,901, . 2.872. 2.861 . 2.845. 2.862.

No balancing while discharging. This is not a defect in one battery cell, it is always a random cell that hits the upper or lower boundary before the others

Any ideas?

Batteries are new from brand manufacturer. (8 x 110Ah LiFePo)

Daly BMS 24V 8S 100A (R16A-GA14) with BT/UART + CAN/485. Software version/Firmware: 20201205-1.01G . BTW: Where can I get new firmware?



--------------------------------


Problem number two:


When charging, the Smart BMS application on the first page shows " minus " ( for example " -4A " ) Once discharged, it does not show a minus. ( for example " 4A " ) This should be reversed, minus must always be displayed when discharging. But it's not. What's the problem?

Thanks

 

[Bob B]

I would expect the first issue to be normal operation for that BMS if the pack was not properly top balanced. .... it has VERY little balance current.

For the second problem ... is it possible you have the B- and C- wires reversed.?

 

[Steve_S]

Charging: That is the normal & expected behaviour for any BMS.
Passive Balancing is not very effective with Large Capacity cells like 100AH. It is even less effective with unmatched bulk cells.

Discharging: Is also the correct behaviour for Low Volt Protection.

What you are seeing is something commonly referred to as Runner Cells, which can occur above 3.450Vpc or below 2.85Vpc +/-.

Did you top balance the cells prior to assembling the pack ?
If not it should be done and this can also be a correction for the current issue.

Problem 2: Possibly Shunt Wires Reversed, otherwise things would be messed up with SOC & cell voltage readings. I am not familiar with that model of BMS, someone else with direct 1st hand knowledge with them will chime in.

 

[Marten]

I would expect the first issue to be normal operation for that BMS if the pack was not properly top balanced. .... it has VERY little balance current.

For the second problem ... is it possible you have the B- and C- wires reversed.?

(I apologize for my poor English)


Yes, the packaging is well balanced.

It has very litle balance current ? Not good for me :-(

For the second problem - No, B- and P- wires are well connected. (B- to battey, P- to the power supply)

I see the same problem with the German seller in his video here:

Look at this Time " 4 min 33 sec " ( charging is shown, but the app displays a minus )

This Daly BMS I bought from him...

 

[Marten]

Charging: That is the normal & expected behaviour for any BMS.
Passive Balancing is not very effective with Large Capacity cells like 100AH. It is even less effective with unmatched bulk cells.

Discharging: Is also the correct behaviour for Low Volt Protection.

What you are seeing is something commonly referred to as Runner Cells, which can occur above 3.450Vpc or below 2.85Vpc +/-.

Did you top balance the cells prior to assembling the pack ?
If not it should be done and this can also be a correction for the current issue.

Problem 2: Possibly Shunt Wires Reversed, otherwise things would be messed up with SOC & cell voltage readings. I am not familiar with that model of BMS, someone else with direct 1st hand knowledge with them will chime in.

I did top balance the cells prior to assembling the pack. Wires are not reversed, its ok. Look at the video by a German seller,he has it the same way.

I think I will need an active blancer because this BMS does not balance battery cells when discharging, but only when charging.

I still don't know why the app displays a "minus" when charging. It's not an application problem. (I've tried other versions of the app)

Thank you for your answers and apologies again for my poor English.

 

[Bob B]

Does the SOC work as expected?

 

[Marten]

Does the SOC work as expected?

No. "0 %" point is not reached, but "100" % is always reached.

 

[Bob B]

Maybe someone will check in who knows more about the Daly BMS. I don't have one and don't know what parameters might be available.
If the current display is accurate, but backwards and the BMS works well otherwise .... I would probably just live with it.

 

[GXMnow]

First thing I would do is put a moderate load on the system and watch the battery state of charge. See if it is going up or down. That will show for sure if the current is reversed. I saw this once before, on a "smart" BMS on this forum. I will try to find the thread. It turned out that the calibration data was entered in reverse causing the current to show negative.

I don't have a DALY, but my JK BMS is similar and it has a voltage and current calibration function. In the App, there should be a selection to calibrate the current and voltage readings. You supply a charge or discharge current, and then you enter the correct value. Be sure to enter a positive value when charging and a negative value when discharging. The BMS will then scale it's internal reading to match the number you enter.

As for the shut off, it does sound like it is doing it's job when it sees a cell goes out of range. Re-check all of the cell connections and the balance leads, and compare the cell voltages to a known good volt meter. My balance lead developed a bad connection where it plugged into the balancer and that made it show 2 cells with very low voltage. Both the high current connections and the balance wires all need to be making good connections. Most of the smaller DALY BMS units only have 30 milliamps of balance current. And it is common practice on LFP cells to only balance during charging and just pull down the high cells. Even if the cells are not perfectly matched, doing a solid "top balance" should still work fine with this type of balancing. To get a good balance on LFP cells, you do need to pull the voltage of every cell into the upper knee. And then they should all be held at the same terminal voltage for a while. This is why most people recommend connecting all of the cells in parallel. Then you just hold them all above 3.45 volts for a while, and they should all balance at near full charge. While discharging, the weakest cell is going to hit the low voltage cut off point first. Even a fairly high power active balancer is not going to do much to stop that from happening. My JK BMS cann pull or push about 2 amps, but to only one cell at a time. It pulls from the cell with the highest voltage, and then pushes to the cell with the lowest voltage. At best, it can only hold that 2 amps for less than 1/2 the time. On most other BMS units, the balancing is only done by connecting a resistor to any cell that is higher than the rest of the pack, and the "balance start voltage". If the cells ae well top balanced, and the only issue is a cell with a bit less capacity, you still need very little balance current. Sure, the weak cell will discharge a bit faster, and may cause the BMS to go into under volt lock out, but it is doing it's job to protect the cells. When the pack is being charged again, that weak cell will also charge back up faster. In theory, it should come back into balance with all of the other batteries in the system. If you pulled out 30 amp hours, it should take the same 30 amp hours to top up all of the cells again. Mismatched cells will diverge in the discharge state, but then converge again at full charge. Try at least one cycle with it charging at a much slower rate. That should allow the low balance current more time to try and pull the cells back into balance.

 

[Marten]

Maybe someone will check in who knows more about the Daly BMS. I don't have one and don't know what parameters might be available.
If the current display is accurate, but backwards and the BMS works well otherwise .... I would probably just live with it.

I agree, but there are two drawbacks:

Only 1 battery cell is always fully charged at 3.65V. Then the BMS stops charging for the whole pack. The other 7 cells have 3.4V . 3.35V ... etc. (This is not fully charged)

If 1 battery cell is dead to 2.5V, BMS is stopped even though the other 7 cells still have 2.8 - 2.8V available. (Stopping BMS will happen too soon)

These batteries are for the electr. wheelchair. :-( Not for solarsystem. We need to use as much capacity as possible.

 

[Bob B]

I agree, but there are two drawbacks:

Only 1 battery cell is always fully charged at 3.65V. Then the BMS stops charging for the whole pack. The other 7 cells have 3.4V . 3.35V ... etc. (This is not fully charged)

If 1 battery cell is dead to 2.5V, BMS is stopped even though the other 7 cells still have 2.8 - 2.8V available. (Stopping BMS will happen too soon)

These batteries are for the electr. wheelchair. :-( Not for solarsystem. We need to use as much capacity as possible.

The solution to that is to try top balancing the cells again to see if it solves the problem .... or add an active balancer.
The Daly BMS would only have enough balance current to keep these large cells in balance if they are very well matched cells and very well top balanced.

 

[Marten]

First thing I would do is put a moderate load on the system and watch the battery state of charge. See if it is going up or down. That will show for sure if the current is reversed. I saw this once before, on a "smart" BMS on this forum. I will try to find the thread. It turned out that the calibration data was entered in reverse causing the current to show negative.

I don't have a DALY, but my JK BMS is similar and it has a voltage and current calibration function. In the App, there should be a selection to calibrate the current and voltage readings. You supply a charge or discharge current, and then you enter the correct value. Be sure to enter a positive value when charging and a negative value when discharging. The BMS will then scale it's internal reading to match the number you enter.

As for the shut off, it does sound like it is doing it's job when it sees a cell goes out of range. Re-check all of the cell connections and the balance leads, and compare the cell voltages to a known good volt meter. My balance lead developed a bad connection where it plugged into the balancer and that made it show 2 cells with very low voltage. Both the high current connections and the balance wires all need to be making good connections. Most of the smaller DALY BMS units only have 30 milliamps of balance current. And it is common practice on LFP cells to only balance during charging and just pull down the high cells. Even if the cells are not perfectly matched, doing a solid "top balance" should still work fine with this type of balancing. To get a good balance on LFP cells, you do need to pull the voltage of every cell into the upper knee. And then they should all be held at the same terminal voltage for a while. This is why most people recommend connecting all of the cells in parallel. Then you just hold them all above 3.45 volts for a while, and they should all balance at near full charge. While discharging, the weakest cell is going to hit the low voltage cut off point first. Even a fairly high power active balancer is not going to do much to stop that from happening. My JK BMS cann pull or push about 2 amps, but to only one cell at a time. It pulls from the cell with the highest voltage, and then pushes to the cell with the lowest voltage. At best, it can only hold that 2 amps for less than 1/2 the time. On most other BMS units, the balancing is only done by connecting a resistor to any cell that is higher than the rest of the pack, and the "balance start voltage". If the cells ae well top balanced, and the only issue is a cell with a bit less capacity, you still need very little balance current. Sure, the weak cell will discharge a bit faster, and may cause the BMS to go into under volt lock out, but it is doing it's job to protect the cells. When the pack is being charged again, that weak cell will also charge back up faster. In theory, it should come back into balance with all of the other batteries in the system. If you pulled out 30 amp hours, it should take the same 30 amp hours to top up all of the cells again. Mismatched cells will diverge in the discharge state, but then converge again at full charge. Try at least one cycle with it charging at a much slower rate. That should allow the low balance current more time to try and pull the cells back into balance.

OMG! Thank you very much for the information. I will now do your procedure, which you recommended, that is very valuable to me!


BTW: Maybe I use a high charging current for this BMS. This BMS (Daly 8X 24V 100A) can be charged max. 50A. I use a 20A via this charger:

GWL/POWER Charger 12V/20A For LFP/LTO Cells (4 Cells), BMS Input | shop.GWL.eu

High Power selectable charger 12V/20A for LiFePO4 and LTO batteries with BMS support.

shop.gwl.eu

This Daly BMS have a very small balancing current, so it doesn't balance well when charging....with fast charger 20A ( ??? )

Now I perform new charging with a very small current. ( 4A only as initialization . Again ) Then I will carry out the procedure you wrote here.

I don't know how to find out if there's a plus and a minus reverse inside BMS, but I'm surprised the German seller from the above video has the same problem with "minus" on App while charging


Thank you very much and apologies again for my very poor English.

 

[Marten]

The solution to that is to try top balancing the cells again to see if it solves the problem .... or add an active balancer.
The Daly BMS would only have enough balance current to keep these large cells in balance if they are very well matched cells and very well top balanced.

Ok. Now I charge the battery cells with a small current. (4A) After that, I'll do the discharging, maybe it'll be okay. If not, I'll have to buy an active balancer.

BTW: I might have to buy a really active balancer because Daly BMS doesn't do balancing during discharging. Therefore, there is a big difference when hitting the bottom point 2.5V

 

[Bob B]

Ok. Now I charge the battery cells with a small current. (4A) After that, I'll do the discharging, maybe it'll be okay. If not, I'll have to buy an active balancer.

If you truly want to top balance them .... you would need to charge them in parallel. There are a number of threads on here about top balancing if you do a search.

 

[Marten]

If you truly want to top balance them .... you would need to charge them in parallel. There are a number of threads on here about top balancing if you do a search.

Is that necessary? I don't have a charger with 3,6V .... but 24V/20A only :-( I can balance cells only by a parallel connection between battery cells.

 

[time2roll]

Since it is a different cell each time I recommend stop charging at 27.0 volts and stop discharging at 24.0 volts. I believe you are still getting most of the energy out of the battery. If the cell delta at the top is able to equal out after a month or two then increase the charging voltage to 27.5 and see what goes.

 

[Bob B]

Is that necessary? I don't have a charger with 3,6V .... but 24V/20A only :-( I can balance cells only by a parallel connection between battery cells.

Just putting them in parallel won't work unless the cells are in the upper knee of the voltage curve.

You could also try to assist the balancing by bleeding off the high cell with a resistor .... others have used light bulbs, etc
Do a search for manual balance cells.

 

[Daddy Tanuki]

wheel chair is similar to a EV. bottom balance and then charge to the Daly limit. 3.65... this will allow the same bottom draw. it is how you are using the cells that determine if it should be top, or bottom balanced. my DALY (top balanced for solar inverter use) shoes the same annoying -amps when charging... it is a failure on the code writer for the BMS. it still works fine... the SCO meter is accurate, just the symbols for _ and + are flip flopped in the code. I would bottom balance and go from there as a wheelchair should run off of what its lowest percentage is...that way you can guage when its going to run out of power and not leave you stranded... just like an EV (electrical vehicle). Anddo not worry about your english abilities.. just note it so other can take that into consideration and after that tell them to have a nice day. (we call them Grammar or Spelling nazi's... thats whay they are more concerned with grammar and spelling then they are the actual content.. fark them.

 

[Marten]

Just putting them in parallel won't work unless the cells are in the upper knee of the voltage curve.

You could also try to assist the balancing by bleeding off the high cell with a resistor .... others have used light bulbs, etc
Do a search for manual balance cells.

The balancing by bleeding off the high cell with a resistor .... I've done that with light bulbs several times. Some cell was always first on point 2.5V and turned off BMS, even though the other 7 cells still had 3.8V available.Thank you for your answers.

 

[Marten]

wheel chair is similar to a EV. bottom balance and then charge to the Daly limit. 3.65... this will allow the same bottom draw. it is how you are using the cells that determine if it should be top, or bottom balanced. my DALY (top balanced for solar inverter use) shoes the same annoying -amps when charging... it is a failure on the code writer for the BMS. it still works fine... the SCO meter is accurate, just the symbols for _ and + are flip flopped in the code. I would bottom balance and go from there as a wheelchair should run off of what its lowest percentage is...that way you can guage when its going to run out of power and not leave you stranded... just like an EV (electrical vehicle). Anddo not worry about your english abilities.. just note it so other can take that into consideration and after that tell them to have a nice day. (we call them Grammar or Spelling nazi's... thats whay they are more concerned with grammar and spelling then they are the actual content.. fark them.

Reversed plus a minus it is a failure on the code writer for the BMS? Is there any way to repair it? Does that mean there's a fault on the manufacturer's side? This means it is a defective product and I can return this BMS back to the seller ? It's frustrating.
For a wheelchair, I need as much energy as possible, which is why I wanted good batteries and BMS. I didn't know there'd be so much work to do.