Active Balancer Start Balancing Voltage Confusion

[zedconnor]

I have seen people say start balancing at 3.3V.
And others saying anything below 3.45V is ineffective.

Assume a battery pack 25.6V 200Ah (8x 200Ah cells)
They're not balanced. But assembled into a pack and already in use.
Daly Smart BMS+ Daly Smart Active Balancer 1A

(Load is Around 300~600W loads)



What start balancing setting would be best for this pack with a 1A Smart Active Balancer?(balancer is already connected to the pack. Daly Bms passive balancing seems useless.)

Thanks in advance!

(Inverter charging current is 30A and there is no solar. Only batt+inv)

 

[rodrick]

I wouldn’t start below 3.4

 

[Steve_S]

- PASSIVE Balancing is intended for Matched & Batches cells below 100AH, quite useless above that AH or with non-batched cells. It only burns off High Voltage from cells, it does not transfer it.
- Active Balancing MOVES power from a High Cell to a Low Cell. We generally suggest 1A Active per 100AH of Capacity.

I have done extensive testing from light to extreme use, bordering on abuse (Thrash Tests) with assorted cells A, B, Bulk (broker crap) and even "genuine" used EV LFPcells. Believe it or not, the Sweet Spot is 3.42 Volts with a 0.010 Cell Differential.

Of course this is reliant also on the Charge Profile so that it allows for the cells to be topped & balanced out at the top of the working Voltage Range.

Recommended Profile for SCC, inverter/Charger etc.

Bulk & Absorb: 27.6V (3.45vpc) Absorb for 45 minutes (some call this boost) *Absorb generally never actually runs the full 45mins due to EndAmps
Equalize: OFF
Float 27.5V (3.437vpc)
MIn Volts: 21.2 (2.650vpc) (to prevent bricking BMS is cells too low)
Max Volts: 28.6 (3.575vpc)
Rebulk Voltage: 25.6 (3.200vpc)
End Amps: (*1) (** Allows for full Saturation at set Float Voltage)
(*1): End Amps is calculated as IE: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
(**): Float is Constant Voltage/Variable Current, it finished the top 5-7% of cell charging.
- BULK/Absorb = Constant Current/Constant Voltage) This is for 0%-95% of charge process for LFP.
NB: EndAmps = TailCurrent Depends on Company for terms.
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.

 

[zedconnor]

- PASSIVE Balancing is intended for Matched & Batches cells below 100AH, quite useless above that AH or with non-batched cells. It only burns off High Voltage from cells, it does not transfer it.
- Active Balancing MOVES power from a High Cell to a Low Cell. We generally suggest 1A Active per 100AH of Capacity.

I have done extensive testing from light to extreme use, bordering on abuse (Thrash Tests) with assorted cells A, B, Bulk (broker crap) and even "genuine" used EV LFPcells. Believe it or not, the Sweet Spot is 3.42 Volts with a 0.010 Cell Differential.

Of course this is reliant also on the Charge Profile so that it allows for the cells to be topped & balanced out at the top of the working Voltage Range.

Recommended Profile for SCC, inverter/Charger etc.

Bulk & Absorb: 27.6V (3.45vpc) Absorb for 45 minutes (some call this boost) *Absorb generally never actually runs the full 45mins due to EndAmps
Equalize: OFF
Float 27.5V (3.437vpc)
MIn Volts: 21.2 (2.650vpc) (to prevent bricking BMS is cells too low)
Max Volts: 28.6 (3.575vpc)
Rebulk Voltage: 25.6 (3.200vpc)
End Amps: (*1) (** Allows for full Saturation at set Float Voltage)
(*1): End Amps is calculated as IE: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
(**): Float is Constant Voltage/Variable Current, it finished the top 5-7% of cell charging.
- BULK/Absorb = Constant Current/Constant Voltage) This is for 0%-95% of charge process for LFP.
NB: EndAmps = TailCurrent Depends on Company for terms.
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.

Thank you for the detailed reply! Really helpful for me!

One thing I don't understand is the Rebulk Voltage , is it same as the "Voltage Point Back To Battery" option in the Inverter? (Inverter is a MUST 3KW PV1800 VPM model. Settings are similar to Growatt.)
Also I am using UTI mode for charging since there is no solar.


And you set the FLOAT Voltage to 3.437Vpc in order to stay ahead of the Start Balance Sweet Spot which is 3.42V, so that the Active Balancer will have alot of time to balance the cells. (Without the cells quickly drifting below 3.4V once charging has stopped.)
Is my understanding of this correct sir?

Otherwise if I set FLOAT to 3.4Vpc but Start Balance Volt to 3.45V, then the cells will have very little time to balance once charging has stopped.(One cell having about 3.5V so charging stopped but all other cells falling below 3.4V)

(Note : The Daly Active Balancer only starts balancing if all cells voltages are above the specified Start Balance Volt )

 

[Steve_S]

I don't know Daly BMS' other than to not bother with them... Sorry I am a JK guy and have worked with several companies, doing various things, including writing their manuals.. Not doing that anymore.

REBULK is used by some companies... Sadly there is NO Standardization on terms which is a MASSIVE PITA! Rebulimnk means that when the pack hist XX.XX volts to restart the Bulk Charging and then Absorb afterwards. It is best to start this when battery pack is 50% SOC or slightly higher to get a good deep full amperage charge to saturate the cells properly.

Yes, FLOAT is just above the trigger and that allows the Active Balancing to occur without doing too much work and slowing the charge process... YES it can slow the charging, this is observable with a LOT of patience. Any cells above 3.42 will have it's voltage transferred to the lowest volt cell in the pack... As 3.400 is the TOP of the Working Voltage Curve, this is the sweetest spot to charge to while allowing for the natural & normal settling.

Even NON-BMS Active Balancers will start to transfer power the moment A cell crosses the trigger point, they do not wait for all cells to be above that point, that is a FAIL ! That is the point, discharge a runner cell to the lowest cell for optimal pack performance.

 

[time2roll]

IMO best to let it balance at all voltages. Anything more than 15mV can be balanced and stop at 5 to 10 mV. The voltages get so close in the middle capacity voltage there should be nothing to do. And if they are that far off the balancer may as well get busy.

Post a screen shot of the cell voltages to see what action is needed.

 

[TheGreenThing]

Hi my inverter is a deye and does not have a absorption time.. how do i balance the cell pack?
My balance starting voltage is set at >54.3V and will stop balance at <53.6V
I have 3 rouge cells usually quickly goes too high or too low during charging and discharging
Max discharge from battery is knly set at 500w with DOD of 51.2V

The manufacturer of my powerwall has set the bms to stop charging when the cellpack hit 56V and the soc will reset to 100%

Solar panel 550W x 10
Inverter deye hybrid 5k
Battery is a 16s generic china powerwall
LFPW-51.2100
Balancer: heltec capacitive type with a30 voltage detection controller

am doing the right way? Or should i just leave the balancer on 24/7 or set the stop balancing at 51.2V

Pls advise

 

[time2roll]

Hi my inverter is a deye and does not have a absorption time.. how do i balance the cell pack?
My balance starting voltage is set at >54.3V and will stop balance at <53.6V
I have 3 rouge cells usually quickly goes too high or too low during charging and discharging
Max discharge from battery is knly set at 500w with DOD of 51.2V

The manufacturer of my powerwall has set the bms to stop charging when the cellpack hit 56V and the soc will reset to 100%

Solar panel 550W x 10
Inverter deye hybrid 5k
Battery is a 16s generic china powerwall
LFPW-51.2100
Balancer: heltec capacitive type with a30 voltage detection controller

am doing the right way? Or should i just leave the balancer on 24/7 or set the stop balancing at 51.2V

Pls advise

With three cells giving trouble I would run the Heltec full time. I would also lower the charging voltage just enough to avoid the cell over volt fault.
Check it again in 30 days and see if the charging voltage can be restored.

 

[TheGreenThing]

With three cells giving trouble I would run the Heltec full time. I would also lower the charging voltage just enough to avoid the cell over volt fault.
Check it again in 30 days and see if the charging voltage can be restored.

I dont think i can set the charging voltage to a constant voltage.. there are no such feature in my deye inverter..
Although deye has a feature that you could set the
Float voltage, absorption voltage, equalization voltage which is all set to 55.2V but always see the charging voltage higher that 55.2v

Should i just set the balancer to turn on at 54v then shut off at 51.2v?
so the balancer would turn off during charging phase whenever the battery goes to to 51.2v DOD (everyday usage DOD 51.2V)

 

[time2roll]

If the balancer must be switched on/off I would turn on when the high/low cell delta exceeds 35 mV. These balancers are not fast. More time will be better than less.

Is there a temperature compensation adjustment? This could drive the voltage higher when things are chilly. Set the compensation to zero if available.

 

[hwy17]

Should i just set the balancer to turn on at 54v then shut off at 51.2v?

More like start at 54.4 stop at 54.4. Or higher.

 

[TheGreenThing]

If the balancer must be switched on/off I would turn on when the high/low cell delta exceeds 35 mV. These balancers are not fast. More time will be better than less.

Is there a temperature compensation adjustment? This could drive the voltage higher when things are chilly. Set the compensation to zero if available.

Temp inside the batt case stays between around 31-35
I live in a tropical climate

 

[TheGreenThing]

More like start at 54.4 stop at 54.4. Or higher.

This would be ideal if the deye has absorption time. Unfortunately, the inverter stops the charging when the battery pack reaches 56v then i could here a clicking aound from the battery disengaging contacts then the battery pack will slowly decrease and will stay at 53.6v (rest)

 

[TheGreenThing]

I would really like to hear your opinion or suggestions. I need to dismantly my powerwall to adjust the start/stop voltage