Daly BMS Will Not Balance

[Sabre36]

We have a couple of cheap LiFePO4 100Ah drop-in batteries (brand not important) here in the shop that feautre a Daly BMS. When ever we fire up a charge source the immediately trip the BMS on High Voltage. OK, no problem we've seen this before with elcheapo LFP drop-in batteries. We usually open the app and try to figure out where the lowest voltage is where the cells begin to balance, set it just a tad higher, like 0.1V higher, walk away for a while and let the cells balance. We did this...

We connected this battery to our labs equipment and set the power supply for 14.1V, after seeing in the APP that the manufacturer has it set to initiate balancing at 3.500 VPC.. I assume all is well and good. I let it balance for four hours and then turned the voltage up to 14.4V (manufacturers recommended charge voltage) and after a very brief in-rush the Daly disconnected the Charge FET's. One cell had hit 3.75V and initiated another disconnect. What the heck is going on here?

I attempt another re-balnce by applying a DC load to pull the voltage back down a bit to re-engage the charge FET's. I dial voltage back down to 14.1V, from 14.4V, and the BMS starts to balance. As I am standing there, and just before the BMS disconnects at 3.75V, the "Balancing" indicator light turns off! At this point in time the cells were:

3.731V
3.495V
3.427V
3.482V

I shut down charge, apply a DC load and repeat the process. Again, balancing initiates but as soon as accepted current drops to 0A (based on the Daly shunt info) the balancing instantly turns off.

We have tried every possible setting in this BMS (Yes, we have the password) and yet nothing allows it to balance when or if the cells are accepting 0.00A. What kind of BMS will not and does not use the chargers power or the high cell voltage to shunt current to the lower cells? If this is actually the way this BMS is designed to operate, it's a complete joke. I have spent hours this morning searching and have not found anyone reporting this behavior with a Daly BMS? While we've seen these issues before we can always set a low voltage and sit back and allow the cells to eventually come into balance. The Daly BMS will not allow that???

I am sure I am missing something but literature is impossible to find on this Daly BMS, the company does not answer emails. The documentation on the battery is worse than a joke. On top of all this the battery case is glued together with what appears to be a SuperGlue material and if any attempt is made to open this battery it will be 100% destroyed.

It appears the cells inside are grossly mismatched, the Daly can't balance the cells, and the ramp down from the cells reaching 3.40V is so fast that there is insufficient time to re-balance before the cells are accepting 0.00A.... The BMS it seems can only balance when the cells are actively accepting current despite a 0.304V imbalance!! At this level of imbalance, and the minuscule balance current, the cells will never, ever balance out..

Is this typical of the Daly BMS's?
Why does the cycle counter not work?
What is wrong with the SoC feature on this BMS? It is worse than a joke.

 

[John Frum]

What kind of BMS will not and does not use the chargers power or the high cell voltage to shunt current to the lower cells?

Most of them.

Commodity fet based bms just apply a resistive load to the high cell(s).
They don't shunt the current to the lower voltage cells.
Daly probably can balance even when its not charging.
There should be a parameter to enable this.
I would only enable it to adress the kind of problem you are having but it should whittle away at the high cells without any charge current or even charge voltage.

 

[Sabre36]

Most of them.

Commodity fet based bms just apply a resistive load to the high cell(s).
They don't shunt the current to the lower voltage cells.
Daly probably can balance even when its not charging.
There should be a parameter to enable this.
I would only enable it to adress the kind of problem you are having but it should whittle away at the high cells without any charge current or even charge voltage.

I realize they don't "move" current and just burn it off but this allows the other cells to catch up, poor word chosen on my part...

This Daly WILL NOT balance when not charging. The light for balancing remains OFF. There is nothing in the app that will allow for this. Every parameter, setting etc. has been tried and tested.

 

[mmame]

There exists a cell Voltage setting at which the balancing shall start. By default, this value is pretty high. Maybe reduce that value to a reasonable low value.
And: Daly BMS have a very low balancing current. You can try to use a lab supply with current limit set to i.e. 100mA to give the daly more time to balance.

 

[Sabre36]

There exists a cell Voltage setting at which the balancing shall start. By default, this value is pretty high. Maybe reduce that value to a reasonable low value.
And: Daly BMS have a very low balancing current. You can try to use a lab supply with current limit set to i.e. 100mA to give the daly a longer chance to balance.

It is set at 3.50V but has been set as low as 3.40V then 3.45V, diff voltage has also been adjusted eight ways from Sunday. Already tried our low amp power supplies, no go and balancing still gets disabled once 0.00A is detected.

 

[MisterSandals]

I let it balance for four hours and then turned the voltage up to 14.4V (manufacturers recommended charge voltage)

Given that there is very little battery capacity above 3.5V per cell, is there a reason you couldn't implement a charge profile that will allow the runaway cell to stay within BMS parameters? If you had it to 14.1V without issues, maybe your customer can get by using only 99.5% of the battery capacity.

 

[Sabre36]

Given that there is very little battery capacity above 3.5V per cell, is there a reason you couldn't implement a charge profile that will allow the runaway cell to stay within BMS parameters? If you had it to 14.1V without issues, maybe your customer can get by using only 99.5% of the battery capacity.

I had it at 14.1V for the first couple of cycles and it was ok other than one cell always going over 3.65V. I then ran a capacity test and charged it back up and now it is so out of balance that it will trigger a BMS disconnect at just a 14.0V charge.

 

[mmame]

Discharge the battery to i.e 3.35v/cell, set balance start to 3.35V, balance voltage to 0.01V and use a bench supply set to 14.4V (leads disconnected) plus current limit set to i.e 100mA. Then try to charge.

 

[John Frum]

@Sabre36
If (

black box battery​

and cell_is_a_runner​

and its_under_warranty​

) then {

let the vendor make it right​

}

 

[Sabre36]

@Sabre36
If (

black box battery​

and cell_is_a_runner​

and its_under_warranty​

) then {

let the vendor make it right​

}

Unlikely in this case.

 

[Sabre36]

Discharge the battery to i.e 3.35v/cell, set balance start to 3.35V, balance voltage to 0.01V and use a bench supply set to 14.4V (leads disconnected) plus current limit set to i.e 100mA. Then try to charge.

As mentioned I have already tried that at 3.40V and I will give it a go at 3.35V if the app will allow it.. I know how to set a power supply and most of our power supplies are higher end and are equipped with v-sense leads anyway.

 

[mmame]

So, the BMS does not balance at all even while charging? Then... If all settings are correct/met, the BMS must be defective.

 

[Sabre36]

So, the BMS does not balance at all even while charging? Then... If all settings are correct/met, the BMS must be defective.

It will begin to balance so long as current is flowing into the cells. The problem is these cells charge so fast from about 3.4V on that balancing time is insufficient before the charge FET's get tripped by cell HV. I am now seeing how low I can initiate balancing as setting it at 3.40V was still not enough time.

I am just now discovering that if I drop charge amperage below about 2A the BMS will not balance.

 

[mmame]

If I remember right, this BMS can only balance wit 70mA or so. Thus, charging with 2Amps will almost immediately trigger High voltage cell disconnect when the cells are heavily dysbalanced.

Maybe calibrating 0A current may help...?

 

[MisterSandals]

Unlikely in this case.

OK, warranty and return "unlikely" so...

Open it up to see if there is something that can be fixed? Loose wire, corrosion, ??

If you find the BMS, maybe the balance leads from BMS are accessible for use with dedicated, high amp balancer (temporarily or permanently with a splice to use BMS and balancer).

 

[John Frum]

OK, warranty and return "unlikely" so...

Open it up to see if there is something that can be fixed? Loose wire, corrosion, ??

If you find the BMS, maybe the balance leads from BMS are accessible for use with dedicated, high amp balancer (temporarily or permanently with a splice to use BMS and balancer).

If you have can open the pack and you have a bench psu you can top off each cell see if it will hold balance.

 

[mmame]

..even access to the balance wires would help. But housing seems to be glued...

 

[John Frum]

..even access to the balance wires would help. But housing seems to be glued...

two words

Oscillating

Tool

 

[mmame]

Heatgun ?
Edit: found this, so that minimum 2A charge current seems to persist... https://diysolarforum.com/threads/cannot-get-daly-200a-smart-bms-yo-balance.26269/post-310680

Maybe we can circumvent that ugly limit...? I'm wondering what will happen when we discharge the battery with i.e 4A and while discharging is running, calibrate that value as "0A current". When disconnecting that load, the BMS might think that we're now charging with 4Amps and does start balancing...?
Of course, after balancing, 0A calibration has to be redone with proper values or strange things may happen...

 

[Sabre36]

Heatgun ?

No go at all. What ever it is guled with is not softening with heat...