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LiFePO4 won't charge - BMS issue ?

Lonemi

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Joined
Jan 10, 2023
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21
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Italy
Hello everyone !

Today I had my very first big issue with my LiFePO4 battery pack, to be precise, I am unable to top balance it.

First of all I connected my 8 x 52Ah LiFePo4 cells in parallel and started to top balance them with a common drone battery charger, with a normal setting of 3.65V per cell charge.

Without days and no real success they were stuck at 3.36V per Cell, and since the charger is inappropriate to top balance I chose another method, to put them in series with the BMS to charge to almost full and then switch back to parallel to finish the top balance.

The issue is that, since I do not have a bench power supply, I am feeding current via 2 x 24V 150W Led driver boards ( in series so 48V, 6.8A and 150W total) through a Solar charge controller which works as a charger. The latter is then connected to the Daly 80A BMS.

The problem is that the BMS, I suppose, cuts the charging process because receives too much current in a very short time, could this be ?

I will attach all my BMS settings in order to show you my situation.

Hope this could be solved, thank you everyone !
 

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Hello everyone !

Today I had my very first big issue with my LiFePO4 battery pack, to be precise, I am unable to top balance it.

First of all I connected my 8 x 52Ah LiFePo4 cells in parallel and started to top balance them with a common drone battery charger, with a normal setting of 3.65V per cell charge.

8cells x 52Ah in parallel is 416Ah

How much current does this "common drone battery charger" supply? If it's 5amp you could be looking at 3.4 days to top balance

Without days and no real success they were stuck at 3.36V per Cell, and since the charger is inappropriate to top balance I chose another method, to put them in series with the BMS to charge to almost full and then switch back to parallel to finish the top balance.

The issue is that, since I do not have a bench power supply, I am feeding current via 2 x 24V 150W Led driver boards ( in series so 48V, 6.8A and 150W total) through a Solar charge controller which works as a charger. The latter is then connected to the Daly 80A BMS.

The problem is that the BMS, I suppose, cuts the charging process because receives too much current in a very short time, could this be ?

I will attach all my BMS settings in order to show you my situation.

Hope this could be solved, thank you everyone !

Despite what some will say, running a power supply into a MPPT is not a great idea. MPPT expects a PV array, it is acceptable to directly short a PV array. When you hook a PSU to this, the MPPT can/will load it down possibly to the point of shorting it, then your PSU may shutdown, and restart, etc..
 
Tomorrow morning I will try with 300W Solar Panels instead of the PSU, but I have a feeling nothing will change...it seems like cells won't accept charge even though they are brand new, it looks like BMS cuts the charge without any reason.

To parallel top charge I have hooked for three days two ISDT D2 Chargers set to 10A each, but they give out only 3A amp during charge.
 
I have tried with both alligator clips and ring terminal but there were no difference at all. I believe that when the V diff. is so low (3.4v to 3.65v) the charger has an output limit
 
Why do you think they are not charging? In the screen capture the charging MOS is on. Patience is a virtue
Edit.. have you verified the charger output with a voltmeter?
 
I believe that when the V diff. is so low (3.4v to 3.65v) the charger has an output limit
Yea, i am surprised it charges 3.65V from 3.4V at all. I have only tried Battgos from 12V battery.
Wonder if there might be an input amp draw limit involved too.
In the screen capture the charging MOS is on.
Yes and a glance at the BMS settings show cell over voltage too high at 3.75V, battery over voltage at 30V.

I would change these to conservative values of 3.63V and 29V.
 
Tomorrow morning I will try with 300W Solar Panels instead of the PSU, but I have a feeling nothing will change...it seems like cells won't accept charge even though they are brand new, it looks like BMS cuts the charge without any reason.

To parallel top charge I have hooked for three days two ISDT D2 Chargers set to 10A each, but they give out only 3A amp during charge.

I use a ISDT Q8, You need to use the balance/sense leads to get the full power. Else it thinks the voltage is higher than it is.
 
Why do you think they are not charging? In the screen capture the charging MOS is on. Patience is a virtue
Edit.. have you verified the charger output with a voltmeter?
Yes I did, they are charging but I believe there is a sort of resistance to charge because some cells remain always the same voltage for days
 
Yea, i am surprised it charges 3.65V from 3.4V at all. I have only tried Battgos from 12V battery.
Wonder if there might be an input amp draw limit involved too.

Yes and a glance at the BMS settings show cell over voltage too high at 3.75V, battery over voltage at 30V.

I would change these to conservative values of 3.63V and 29V.
Thank you ! I will change these values as soon as possible, in either cases it do not justify why the bms goes in overvoltage/overcharge...
Hope to understand why it cannot accept 150W at 48V via SCC, it is driving me mad o_O
 
Yes I did, they are charging but I believe there is a sort of resistance to charge because some cells remain always the same voltage for days

LiFePO4 has a rather flat charge/discharge curve. So what you're seeing is not necessarily abnormal.

We see this a lot with people new to LifePO4
 
Yea, i am surprised it charges 3.65V from 3.4V at all. I have only tried Battgos from 12V battery.
Wonder if there might be an input amp draw limit involved too.

Yes and a glance at the BMS settings show cell over voltage too high at 3.75V, battery over voltage at 30V.

I would change these to conservative values of 3.63V and 29V.
I see, maybe my charger is more suitable ? Who knows !

Are these SCC values correct for LiFePO4 ? Maybe they are the cause why BMS goes in safety mode ?

I have :

HVD = 29,6V high voltage disconnect
HVR = 29.2V high voltage reconnect
Bulk = 29V
Equalize = 29V
Float = 27.6V
LVR = 25.6V low voltage reconnect
LVD = 22.2V low voltage disconnect
 
LiFePO4 has a rather flat charge/discharge curve. So what you're seeing is not necessarily abnormal.

We see this a lot with people new to LifePO4
I understand, thank you very much !

In either cases I am more worried with the PSU problem rather than cell voltage
 
Lower your bulk to 28 volts. Try and get the battery to fully absorb at 3.5 volts per cell first. Then you can raise it in smaller increments higher.
 
I am feeding current via 2 x 24V 150W Led driver boards ( in series so 48V, 6.8A and 150W total) through a Solar charge controller which works as a charger.
Hope to understand why it cannot accept 150W at 48V via SCC, it is driving me mad o_O
In general, SCCs require input voltage at least 5V higher than battery/charging voltage. If your SCC is getting 48V, it may not be capable of charging higher or as high as you want (55V).
 
Yes SCC is getting around 48V, but the battery is an 8s 24V LiFePO4, so it should be high enough to charge it.

I have also recently discovered that adding a 100W resistance in series to the negative cable that goes from PSU to SCC does not trigger the BMS, very odd...it could be related to current and not voltage ? ?
 
Yes SCC is getting around 48V, but the battery is an 8s 24V LiFePO4,
Oops, i missed that.
.it could be related to current and not voltage ? ?
Are there current settings you can experiment with?
I see charge over current protect is 40A yet discharge over current protect is 80A. Is this intentional?

I have also recently discovered that adding a 100W resistance in series to the negative cable that goes from PSU
Gosh i have no idea what this would do. Maybe its a clue that someone else can use.

What solar charge controller? Settings?
 
Oops, i missed that.

Are there current settings you can experiment with?
I see charge over current protect is 40A yet discharge over current protect is 80A. Is this intentional?


Gosh i have no idea what this would do. Maybe its a clue that someone else can use.

What solar charge controller? Settings?
The only current settings are the ones on the BMS protection parameters page, I think...
Yes it is intentional, and I chose it due to the fact that on the BMS there is written Charge Current = 40A (should I increase this ?) and Discharge Current = 80A, the BMS is a Daly 8s 80A.

The SCC is a 30A PWM Ecoworthy. And the settings are these
I see, maybe my charger is more suitable ? Who knows !

Are these SCC values correct for LiFePO4 ? Maybe they are the cause why BMS goes in safety mode ?

I have :

HVD = 29,6V high voltage disconnect
HVR = 29.2V high voltage reconnect
Bulk = 29V
Equalize = 29V
Float = 27.6V
LVR = 25.6V low voltage reconnect
LVD = 22.2V low voltage disconnect
 
Buy yourself a bench power supply, put your cells in parrallel, connect it up and wait :). And I mean wait! You will think it isn’t working. You will want to turn knobs. You will want to play with wires but nooooooo! Don’t touch a thing, just wait! Then the magic happens :ROFLMAO:.
 
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