Multiple active balancers at same time?

[AshleyL]

I have JK-PB2A16S20P with integrated 2A active balancers and 16S Heltec 5A (Currently auto voltage trigger or can be set to manual switch).
Soon, I will have Neey 10A active balancer delivered.
Can I leave all three active balancers activated/on at the same time?

 

[BentleyJ]

First question, how many Amp Hours is your battery(s), do you really need 17A of balancing current. If so, why are the cells so far out of balance to begin with that you need so much?

Second question, Are the connectors and wire gauge on the 10A NEEY really rated for 10A. Their 15A version has much heavier "Phoenix Connector" type screw terminals which are more believable. I have the stand alone JK BMS brand of both the 5A and 10A active balancer and the connectors for the cell wires are much heavier Molex style.

As to your original question. All 3 active balancers can be used together but as the cell voltages converge to equivalency the power flows to and from the balancers will themselves cause small voltage deviations and you will see the balancers rapidly switching between several cells because they are reacting to the induced voltage changes of the other balancers. This will lead to situation where they enter into an endless "circle jerk" with the balancers reacting to phantom cell voltage deviations and never shut off. Probably wouldn't cause a problem but you would just needlessly be shuttling current between cells. Active balancers are efficient but still not 100% so should only used as required.

My advice would be set the balancers to activate only above 3.4V (the knee of the charge curve) and set the cell balance mV in stages. For example.
Set the 10A Neey to something like 25mV. It only kicks in to take care of Gross cell imbalances and then shuts off as they come into balance.
Set the integrated 2A balancer in the BMS to 10mV and let it finish off the last bit of balancing by itself.

Maybe use the Heltec 5A manually and only for cell imbalances of 75mV or more to speed up the process if necessary. Remove it when the balance gets to less than 30mV.

 

[AshleyL]

Oh, I have 16 280Ah Lifepo4 (same battery model bought in 4 units in 4 batches....in different time). Therefore each 4 batches have different SOC. Few weeks ago, I finally bought Growatt SPH 6000 ES Plus and JK-PB2A16S20P which has inverter communication. I selected “LI” in Program 5 and using RS485 communication protocol. However, JK-PB2A16S20P has a bug and that is, if any one of the cell reach OVP, it switches the SOC % to 100% and sends a signal to Growatt to stop charging. It never go into "float" mode and the charging simply stop. Thus, the built-in 2A active balancer and Heltec 5A never have much chance to balance at 3.45v. Currently waiting for JK to provide firmware update fix at end of the month.

There are one batch of 4 cells get fully charged first (which was top balanced) before other cells. My dedicated charger decided to off itself on my 5th cell leaving me with 14 non-top balanced cells

I stumbled upon this forum and read few threads that suggest user to set Growatt Prog 05 to USE mode, Prog 19 to 56.0v and Prog 20 to 55.4v instead of the BMS-Inverter communication.
JKBMS only balance 2A by transferring current by one cell to one cell. Meanwhile, Heltec normally balance by 1A-2.5A depending on voltage deviation as measured by my DC clamp meter.
I set the JKBMS to shut off discharge at 2.8v per cell and growatt will switch over to utility automatically. I make full use of currently available capacity. It just that the balancing kinda........take forever........one of the 14 non-top balanced tends to trigger LVD (only 0.025v deviation between those 14 cells at 2.8v, the 4 top-balanced cells voltage are at 3.1v)

I shall follow your advices in using all three balancing functions. Use Neey to balance at 25mV and JK to balance at 10mV. Guess I will disconnected the voltage trigger relay at Heltec and use manual switch as you recommended.

There is one question on the balancing part. When people mention 2A, 5A and 10A active balancer, what is the wattage being transferred? P= I x V. What is the voltage? Total pack voltage? Or individual cell voltage? I searched around the net and I never really find out answer to my question.

 

[BentleyJ]

You would use the individual cell voltage in the above equation. So for example a 10A balancer would be transferring 10A x 3.45V = 34.5W. Not sure how helpful this information would be since the balancer many times will pull power from 2 or 3 different high voltage cells during one capacitor charge cycle and may then transfer that energy to more than 1 low voltage cell during a single capacitor discharge cycle. You would need to know how many seconds were spent on each cell or in engineering terms called the duty cycle.
I suppose if each balancer channel had a coulomb counter it would be possible to determine which cell(s) seem to need the most balancing attention.

EDIT: I would recommend float charging the battery at 54.8V for 12hrs with the 10A active balancer. That should top balance all the cells. You can extend the time as needed to get everything balanced. While its true that LFP chemistry doesn't need constant float charging and can even be detrimental, at this low of a charging voltage you could even go 24 hrs if that's what it takes to get all the cells balanced.
Ultimately the goal is to have all the cells reach 100% simultaneously without triggering an OVP event.

 

[BentleyJ]

Take a look at the chart attached below. As luck would have it, I float charged my 2 batteries today. This is an excellent example of the behavior of a well balanced battery pack. The Red Amperage line breaks sharply and falls off rapidly when all the cells reach 100% at the same time.

 

[AshleyL]

You would use the individual cell voltage in the above equation. So for example a 10A balancer would be transferring 10A x 3.45V = 34.5W. Not sure how helpful this information would be since the balancer many times will pull power from 2 or 3 different high voltage cells during one capacitor charge cycle and may then transfer that energy to more than 1 low voltage cell during a single capacitor discharge cycle. You would need to know how many seconds were spent on each cell or in engineering terms called the duty cycle.
I suppose if each balancer channel had a coulomb counter it would be possible to determine which cell(s) seem to need the most balancing attention.

EDIT: I would recommend float charging the battery at 54.8V for 12hrs with the 10A active balancer. That should top balance all the cells. You can extend the time as needed to get everything balanced. While its true that LFP chemistry doesn't need constant float charging and can even be detrimental, at this low of a charging voltage you could even go 24 hrs if that's what it takes to get all the cells balanced.
Ultimately the goal is to have all the cells reach 100% simultaneously without triggering an OVP event.

Noted. For time being, I will try to float charge at 54.8v using Heltec 5A while waiting for Neey 10A arrival. It will take a least one or two weeks to balance using Heltec 5A.