Top Balancing a large bank

[Barbuda Cottages]

I'm finally receiving my shipment of 160 x Eve 280AH cells that I purchased from Amy. It took 3 months to get from China to Miami, Miami to Antigua, then Antigua to Barbuda and they are arriving on the cargo boat today !
I've been doing a lot of research on top balancing but I'm not finding a lot of information on balancing a large bank ( 160 cells ) fairly quickly . These cells are replacing a worn out set of AGM batteries that can no longer hold a charge so trying to get these new cells in service as quickly and safely as possible is priority as we are fully off grid and currently need to run a generator 12 hours a day to supplement power .
My thought is to connect 10 sets of 16S as they will eventually be and let the outback system ( solar and gen ) charge them up to full 58.4 volts ? Should I connect the BMS's for the first charge ? The outback system will increase voltage and decrease amperage as the batteries become full . Then pull them apart and connect in parallel , maybe sets of 32 and use a 10amp bench top power supply to finish the balance . I bought 2 power supplies so I could do 64 at a time . or should I just connect 2 sets of 80 and wait for the 2 sets to balance ?
My goal is to try to balance quickly so any suggestions would be appreciated .

 

[Bob142]

Should I connect the BMS's for the first charge ?

Always connect the BMS before you try to charge them in series. Otherwise you'll almost certainly overcharge and potentially ruin some of the cells.

Top Balancing "How to"

For current best practices on top balancing cells, please watch the video and download the PDF at the following page: Top Balancing Cells Using a Low Cost Benchtop Power Supply If you are interested in a more general tutorial of what balancing is about and *Why* to balance, check this out...

diysolarforum.com

 

[jtvt]

I'm only doing 32, but my plan was to make two strings of 16s with bms on each string. Making sure that the BMS high volt cut out actually works before hand(test it on a lower voltage). Then try to use an 18a 48v plug in charger to charge each string until the bms cuts out (3.6v). If that is too slow, then I will replace the charger with panels/generator power (~70-100a). When the bms cut out triggers, I will take the strings apart and parallel two sets of 16 and use a bench top power supply (15v 60a model set to 3.65v) to finish each set.

You absolutely must use a bms.

 

[John Frum]

160 cells makes 10x 16s batteries.
Odds are you get a few less than awesome cells.

Here is roughly what I did with mine...
While the courier waited(gave him a tip for his trouble)
Before you accept delivery.
Inspect the boxes Including the bottoms.
Weigh the boxes.
Verify with your nose that you don't have a leaky cell(the electrolyte has a terrible chemical smell and its toxic).
If all present and correct take delivery.

Open the boxes one at a time and inventory the contents.
Make sure each individual cell is free of physical defects.
For each cell, check the voltage and record it along with a serial number on masking tape that you stick to the cell.
The cells should all be within millivolts.

Do you have an internal resistance tester?
Remember at best a battery has the capacity of its weakest cell.
Please report back on the results of the delivery check.

 

[John Frum]

You have ~1 short ton of cells to inspect.
Probably in 40 boxes each weighing ~50 pounds.

 

[DerpsyDoodler]

You have ~1 short ton of batteries to inspect.
Probably in 32 boxes each weighing ~50 pounds.

I hope he’s got the equipment to get them going. it would really suck doing all that with a single 10 amp bench supply.

 

[Barbuda Cottages]

160 cells makes 10x 16s batteries.
Odds are you get a few less than awesome cells.

Here is roughly what I did with mine...
While the courier waited(gave him a tip for his trouble)
Before you accept delivery.
Inspect the boxes Including the bottoms.
Weigh the boxes.
Verify with your nose that you don't have a leaky cell(the electrolyte has a terrible chemical smell and its toxic).
If all present and correct take delivery.

Open the boxes one at a time and inventory the contents.
Make sure each individual cell is free of physical defects.
For each cell, check the voltage and record it along with a serial number on masking tape that you stick to the cell.
The cells should all be within millivolts.

Do you have an internal resistance tester?
Remember at best a battery has the capacity of its weakest cell.
Please report back on the results of the delivery check.

Thanks for the reply , unfortunately I don't have a choice on what's being delivered , once they arrived in Miami they were transferred to another shipping company to get them to me here in the caribbean . I'm hoping that because they were on 2 pallets that there was less of a chance of damage , fingers crossed !
I will be testing the internal resistance and checking the appearance of the cells I will report back on status

 

[Barbuda Cottages]

I hope he’s got the equipment to get them going. it would really suck doing all that with a single 10 amp bench supply.

I'm going to try and do most of the initial charging and get them as close to full with the solar and generator , system consists of 60 x 300 watt panels , 4 x outback flexmax 80 charge controllers , 4 x outback 3500 watt inverters , and a kubota 25kw generator .
The tough part is going to be the top balancing with only 2 bench top power supplies .

 

[John Frum]

I'm going to try and do most of the initial charging and get them as close to full with the solar and generator , system consists of 60 x 300 watt panels , 4 x outback flexmax 80 charge controllers , 4 x outback 3500 watt inverters , and a kubota 25kw generator .
The tough part is going to be the top balancing with only 2 bench top power supplies .

Do you have a resistor or capacity tester to draw down a high cell?
Since the cells come effectively bottom balanced during the production process the cell that trips your bms first will very likely be the weak one.

 

[HRTKD]

Patience is key here. I wouldn't rush a set of cells that are critical to my power system.

With the BMS connected I would get the 16s cells to 3.4v, maybe 3.5v. Then reconfigure to 16p and use the bench top power supply to top balance that cell pack.

 

[codfish]

As you and others are suggesting, an initial, low voltage 16s charge with BMS attached seems like the way to start.
But why not continue that way?
Let’s assume you measure the IR, and group cells with similar IR into 16s packs. You package them up with some compression, BMS, fuses, etc.
set the HV cell disconnect ( previously tested) at 3.65v, but set your charger to 3.4v per cell or 54.4v and turn on whatever balancing you have to start at 3.4 or a little below.
And... put them in service. ( on less critical loads)

There will be a few “runners” which shoot well above 3.4 on the first cycle, but are constrained to be less than 3.65. As the packs get cycled, and your balancing works they should get closer. ( weeks ?) When the cell difference gets reasonable at the top of charge, push the pack charge voltage up .5 volt and continue. Eventually you should be able to charge at whatever voltage you settle on for a “top balance” (3.6 / cell?). And then you can drop back to your production, long term profiles.

If you are going to cycle these packs everyday, and you are going to rely on your BMS to protect you and keep things balanced, why not start out that way.
There will obviously be some risk of over voltage disconnects, but you need to plan for BMS disconnects anyway.

 

[Ampster]

I'm not finding a lot of information on balancing a large bank ( 160 cells ) fairly quickly .

The reason there is not a lot of information is because to do it quickly, requires a lot of Amps and the cost of high current power supplies is not cost effective for something that might be done once or twice over the life of the cells. Follow the advice above with patience and you should be okay.

 

[Ampster]

Since the cells come effectively bottom balanced the cell that trips your bms first will very likely be the weak one.

I reread the thread and could not find anywhere it said that the cells were bottom balanced? Some of the runners I have had, tested okay as far as capacity so I would not call them "weak'. Rather, my conclusion was that they were at a different SOC than the others.

 

[John Frum]

I reread the thread and could not find anywhere it said that the cells were bottom balanced? Some of the runners I have had, tested okay as far as capacity so I would not call them "weak'. Rather, my conclusion was that they were at a different SOC than the others.

I am describing what I think is the production process.
The discharge test effectively bottom balances the cells because they are all discharged to 2.5 volts.

 

[Ampster]

I am describing what I think is the production process.
The discharge test effectively bottom balances the cells because they are all discharged to 2.5 volts.

That may indeed be part of the process of "forming" the cells after assembling them. They may also be charged to 3.65 volts to test capacity. Your guess is as good as mine.

 

[John Frum]

That may indeed be part of the process of "forming" the cells after assembling them. They may also be charged to 3.65 volts to test capacity. Your guess is as good as mine.

The SEI formation process fills the cells individually to 3.65 volts effectively top balancing them.

Discharging them to 2.5 volts effectively bottom balances them.

 

[John Frum]

That may indeed be part of the process of "forming" the cells after assembling them. They may also be charged to 3.65 volts to test capacity. Your guess is as good as mine.

My bad, thought I posted the details in this thread.

Another Top Balance Screwup

I was going by the description (Cable Conductor Wire Size: 0.15mm Copper Wire, 18AWG, super flexible;) I did notice the alligators look heftier than others. I still believe it's best to recommend ring terminals and at least 12awg cable especially if someone is complaining their supply isn't...

diysolarforum.com

 

[Ampster]

The SEI formation process fills the cells individually to 3.65 volts effectively top balancing them.

Discharging them to 2.5 volts effectively bottom balances them.

So it would depend on when the cells were removed from that process whether they were top or bottom balanced? I have always assumed it was random except for the cells that continue on to be sold as "matched" cells. The matched cells i have assumed were matched in terms of capacity.

 

[John Frum]

So it would depend on when the cells were removed from that process whether they were top or bottom balanced? I have always assumed it was random except for the cells that continue on to be sold as "matched" cells. The matched cells i have assumed were matched in terms of capacity.

Cells that get diverted before the capacity test are pretty gnarly and wood go to the shady end of the grey market or to landfill.
The capacity test will be a bucketing system.
Cells that pass go on to the self discharge test
Cells that fail by up to ~5% are probably still fine but won't be self discharge tested.
Cells that fail by >~5% are getting progressively dodgy.
This is speculation on my part.

 

[Barbuda Cottages]

As you and others are suggesting, an initial, low voltage 16s charge with BMS attached seems like the way to start.
But why not continue that way?
Let’s assume you measure the IR, and group cells with similar IR into 16s packs. You package them up with some compression, BMS, fuses, etc.
set the HV cell disconnect ( previously tested) at 3.65v, but set your charger to 3.4v per cell or 54.4v and turn on whatever balancing you have to start at 3.4 or a little below.
And... put them in service. ( on less critical loads)

There will be a few “runners” which shoot well above 3.4 on the first cycle, but are constrained to be less than 3.65. As the packs get cycled, and your balancing works they should get closer. ( weeks ?) When the cell difference gets reasonable at the top of charge, push the pack charge voltage up .5 volt and continue. Eventually you should be able to charge at whatever voltage you settle on for a “top balance” (3.6 / cell?). And then you can drop back to your production, long term profiles.

If you are going to cycle these packs everyday, and you are going to rely on your BMS to protect you and keep things balanced, why not start out that way.
There will obviously be some risk of over voltage disconnects, but you need to plan for BMS disconnects anyway.

Balancing the sets the way you are suggesting would make things much easier , and also have the batteries in service much sooner . Would you suggest using the generator to supplement power to make sure I'm hitting the target voltage daily, or just let them cycle normally with the solar ?