Top Balancing "How to"

[Samuel]

Hello!

I hope my ordered 280ah cells will arrive in a few days.
I have no power supply like you use, but I have a charger which also habe a LiFe-Mode.
Do you think it is possible to top balance with this charger https://www.skyrc.com/iMAX_B6mini_Charger

I can set it to LiFe-Mode and choose only 1s.
If I look in the manual, I can find this table.
So, all cells in parallel and the charger set up to 1S it should charge with 3.3V - 3.6V (Nominal 3.3V and Max 3.6V)
Should it work for top balancing? OK, it could take a while with only 6A max. current.

 

[Just John]

I was mostly asking because I wanted to be sure that ‘overcharging’ a cell by repeatedly tipping off to 3.65V will not cause damage or premature degradation/aging.

The manufacturer says capacity is measured from 3.65v to 2.5v, at .5C rates and will last 3000 cycles doing that and degrade to 80% capacity after 3000 cycles. That would imply no problem doing it on an occasional basis. 3.65v is not over charging.

I know in the past that some manufacturers were saying 4.0v to 2.0v, but they also had fewer cycles out of the cells. Most people use more conservative settings, simply because between 2.5v to 3.0v and 3.5v to 3.65v gives at most a couple of amp hours additional capacity. Using the 2.5v to 3.65v settings won't damage a cell, but you will see very significant cell divergence at the high and low ends. For regular use, 95% of the capacity of a cell is "between the knees".

 

[fafrd]

The manufacturer says capacity is measured from 3.65v to 2.5v, at .5C rates and will last 3000 cycles doing that and degrade to 80% capacity after 3000 cycles. That would imply no problem doing it on an occasional basis. 3.65v is not over charging.

I was actually asking about something different - repeated ‘topping off’ to 3.65V with no discharge cycle in between (so different than EVE’s spec which discharges between charge cycles).

I’ve since come to the conclusion that the capacity that develops overnight or even over a few hours after charging to 3.65V is mainly due to self-discharge (~3% / month translates to ~11.7mAh / hour or 140mAh per 12 hours).

So topping off to 3.65 is primarily replacing the charge list to self-discharge and I’m not terribly worried about that causing damage anymore.

But it raises another question about whether each top-off cycle ‘counts’ as much as a full discharge/charge cycle when it comes to lifetime... (same question, different timescale / urgency).

I know in the past that some manufacturers were saying 4.0v to 2.0v, but they also had fewer cycles out of the cells. Most people use more conservative settings, simply because between 2.5v to 3.0v and 3.5v to 3.65v gives at most a couple of amp hours additional capacity. Using the 2.5v to 3.65v settings won't damage a cell, but you will see very significant cell divergence at the high and low ends. For regular use, 95% of the capacity of a cell is "between the knees".

Yes, but unfortunately, these is no data on what % of a full 2.5V to 3.65V cycle you get when charging and discharging to different limits...

If you get more cycles charging between 2.9V and 3.5V, fine. But if it really translates to an added safety margin and actual number of cycles is the same, you’re giving up on 10-15% of the lifetime charge cycling lifetime of your battery for nothing...

 

[Just John]

If you get more cycles charging between 2.9V and 3.5V, fine. But if it really translates to an added safety margin and actual number of cycles is the same, you’re giving up on 10-15% of the lifetime charge cycling lifetime of your battery for nothing...

My measurements put it at more like 2% to a maximum of 5%. I have no clue if it extends cell cycle life, but it certainly makes it easier to keep cells reasonably balanced.

 

[Just John]

I was actually asking about something different - repeated ‘topping off’ to 3.65V with no discharge cycle in between (so different than EVE’s spec which discharges between charge cycles).

Constant "topping off" to 3.65 would (I expect) without any significant discharge cause cell degradation. Other than the manufacturer saying 20 to 50% charge is recommended for storage, I have nothing to back that up. I have been told using a float charge as you would with lead acid is a bad thing. I have no personal evidence or experience to back that up, but it does seem logical since LiFePO4 has significantly less self discharge. I also know that even if you store them at 20 to 50% charge, the manufacturer recommends running a full cycle every 6 months. I think they would last longer if at least a 10 or 20% discharge was done daily, but could not really tell you for another 5 or 10 years if that is true.

 

[Samuel]

Hello!

I hope my ordered 280ah cells will arrive in a few days.
I have no power supply like you use, but I have a charger which also habe a LiFe-Mode.
Do you think it is possible to top balance with this charger https://www.skyrc.com/iMAX_B6mini_Charger

I can set it to LiFe-Mode and choose only 1s.
If I look in the manual, I can find this table.View attachment 36312
So, all cells in parallel and the charger set up to 1S it should charge with 3.3V - 3.6V (Nominal 3.3V and Max 3.6V)
Should it work for top balancing? OK, it could take a while with only 6A max. current.

Is nobody here who can say something about this charger? Is it possible to top balance with it?

 

[HaldorEE]

Top balancing means putting your cells in parallel and charging with a constant current/constant voltage power supply to 3.65V

I used one of these to top balance my 8S 280AH cells.

Set the CV for 3.65V and monitor charging current. When the charge current drops to < 10A you are pretty much done. It is able to output 30A.

https://www.mouser.com/ProductDetail/MEAN-WELL/HRPG-150-33/?qs=N5dOQkml4H9J8NY5iUGGjw%3D%3D

 

[Just John]

Is nobody here who can say something about this charger? Is it possible to top balance with it?

I have no experience with the supply or charger, and I am reluctant to say anything since it seems to be primarily targeted at a very different market segment or function. On paper it seems to be capable of doing it at 6 amps, but reality might be different.

 

[HRTKD]

In theory, since it only charges to 3.6v, instead of the normal 3.65v top balance target, it should be safe to use that charger. But I would still keep an eye on it, with plenty of validation with a standalone voltmeter.

 

[Samuel]

I have no experience with the supply or charger, and I am reluctant to say anything since it seems to be primarily targeted at a very different market segment or function. On paper it seems to be capable of doing it at 6 amps, but reality might be different.

OK, thanks for your answer.
I'll try it with this charger. Otherwise i will buy a stupid powersupply which will deliver 3.6V

 

[Samuel]

In theory, since it only charges to 3.6v, instead of the normal 3.65v top balance target, it should be safe to use that charger. But I would still keep an eye on it, with plenty of validation with a standalone voltmeter.

OK, thanks!
I will observe the charging process. What parameters should I look at? Only that the Voltage must not be over 3.65?

 

[HRTKD]

OK, thanks!
I will observe the charging process. What parameters should I look at? Only that the Voltage must not be over 3.65?

Check each cell. Since your charger only goes to 3.6v you should never see greater than that. However, the question to ask is, are you getting a proper Top Balance if you're only going to 3.6v? I don't know the definitive answer to that. It's a good balance, but is it as effective as going to 3.65v?

 

[snoobler]

Is nobody here who can say something about this charger? Is it possible to top balance with it?

Yes. It has a balance charge mode where you connect all cells to a sensing harness permitting the unit to see all cell voltages. It then charges the series pack and then begins to taper current to hold the peak cell at max voltage and diverts charge to the lower voltage cells.

I have dozens of these and similar chargers.

It has a 60W/6A limit
It can do up to 6 cells in series (more than 2 cells in series will reduce the 6A limit due to the 60W limit)
The balance current is only 200mA

The better questions is, "is this a good tool for top balancing big batteries larger than RC car/plane batteries?"

Not even remotely.

 

[Dogsareloud]

I"m doing single cell topping now with a 10 amp CV/CC power supply. Mainly because I want to see for myself what the visual ques' are from the power supply and get a feel for the process. Like someone above, I only have a 4S setup. So my plan is get all the cells near 3.5...then rack then together in parallel for the final balance.

 

[fafrd]

I"m doing single cell topping now with a 10 amp CV/CC power supply. Mainly because I want to see for myself what the visual ques' are from the power supply and get a feel for the process. Like someone above, I only have a 4S setup. So my plan is get all the cells near 3.5...then rack then together in parallel for the final balance.

I don’t want to encourage anyone to try anything ‘risky’, but I found it pretty easy to use a 10A/30V supply to top balance 280Ah cells at ‘max speed’ of 10A in CC mode.

The main thing is to be realistic about when you are available to keep an eye on things and when you are not.

During the day when I could check in on the cells every few hours (I’d use a timer) I’d set the voltage at the minimum to enter CC mode at 10A (generally around 4.1V in my case).

Overnight I would reduce voltage to enter CV mode at 3.60V (checked with multimeter).

Keeping a log makes it easy to keep track of how quickly cell voltage is rising and, as a general rule, as long as you are below 3.4V you are in the ‘safe’ zone.

From 3.4V to 3.5V it starts becoming increasingly important to track charge rate (rate of voltage increase) if you keep charging in CC mode @ 10A and above 3.5V you either need to be available to babysit it all the way to 3.65V or you should switch to CV mode (which means it will take much longer).

Balancing a pack of multiple cells multiplies all timeframes involved so the ‘worst-case’ (most risky) is to charge a single cell in CC mode but with these large 280Ah cells, it’s pretty manageable (again, as long as you are being realistic about your availability and attentiveness - remember, you are the BMS ).

To give you some idea, it took 40 minutes for my 280Ah cell to go from 3.630V to 3.650V @ 10.1A (so 6.73Ah or 2.4% for that last 20mV). I basically watched the cell for that full final 40 minutes (and was checking every 15 minutes from 3.50V onwards).

If balancing a pack of cells, all of these timeframes increase accordingly. So 8 280Ah cells would take over 5 hours to go from 3.630V to 3.650V and you could pretty easily reduce that final inspection schedule to once every 2 hours above 3.50V; once every 15 minutes above 3.60V; and only needing to watch the final 20mV from 3.63V to 3.65V (which should take about 40 minutes).

 

[FilterGuy]

I don’t want to encourage anyone to try anything ‘risky’, but I found it pretty easy to use a 10A/30V supply to top balance 280Ah cells at ‘max speed’ of 10A in CC mode.

The main thing is to be realistic about when you are available to keep an eye on things and when you are not.

During the day when I could check in on the cells every few hours (I’d use a timer) I’d set the voltage at the minimum to enter CC mode at 10A (generally around 4.1V in my case).

Overnight I would reduce voltage to enter CV mode at 3.60V (checked with multimeter).

Keeping a log makes it easy to keep track of how quickly cell voltage is rising and, as a general rule, as long as you are below 3.4V you are in the ‘safe’ zone.

From 3.4V to 3.5V it starts becoming increasingly important to track charge rate (rate of voltage increase) if you keep charging in CC mode @ 10A and above 3.5V you either need to be available to babysit it all the way to 3.65V or you should switch to CV mode (which means it will take much longer).

Balancing a pack of multiple cells multiplies all timeframes involved so the ‘worst-case’ (most risky) is to charge a single cell in CC mode but with these large 280Ah cells, it’s pretty manageable (again, as long as you are being realistic about your availability and attentiveness - remember, you are the BMS ).

To give you some idea, it took 40 minutes for my 280Ah cell to go from 3.630V to 3.650V @ 10.1A (so 6.73Ah or 2.4% for that last 20mV). I basically watched the cell for that full final 40 minutes (and was checking every 15 minutes from 3.50V onwards).

If balancing a pack of cells, all of these timeframes increase accordingly. So 8 280Ah cells would take over 5 hours to go from 3.630V to 3.650V and you could pretty easily reduce that final inspection schedule to once every 2 hours above 3.50V; once every 15 minutes above 3.60V; and only needing to watch the final 20mV from 3.63V to 3.65V (which should take about 40 minutes).

Everyone has their own approach and their own risk tolerance, but I would never do this myself. The most important tool for top balancing is patience.

 

[Oldtoad]

Top balancing an assembled battery.
Viewed a video showing a ICharger x8 doing at 2ah top balance of an assembled battery.
Is this a satisfactory way to top balance an installed battery that would be a pia to take apart to parallel top balance?

 

[FilterGuy]

Top balancing an assembled battery.
Viewed a video showing a ICharger x8 doing at 2ah top balance of an assembled battery.
Is this a satisfactory way to top balance an installed battery that would be a pia to take apart to parallel top balance?

Can you post a link to the video?

 

[Pyke13]

I should get my 8x 272ah cells in the next week, I’ve read loads on how to top balance but have a question. I’m planning on running 4s2p using 2 bms’s. 2 12v batteries in parallel
do I top balance as a pack of 8 or do I top balance as 2 packs of 4?
I will assemble the packs as 2 separate 4s packs with bms and charge to 14.4v the disassemble to connect in parallel to top balance. Using a bench top cccv 30v 10a power supply. Set to 3.65v cv and allow it to finish balancing the pack.

 

[Dzl]

I should get my 8x 272ah cells in the next week, I’ve read loads on how to top balance but have a question. I’m planning on running 4s2p using 2 bms’s. 2 12v batteries in parallel
do I top balance as a pack of 8 or do I top balance as 2 packs of 4?
I will assemble the packs as 2 separate 4s packs with bms and charge to 14.4v the disassemble to connect in parallel to top balance. Using a bench top cccv 30v 10a power supply. Set to 3.65v cv and allow it to finish balancing the pack.

I've never actually thought about this before, but if it were me, I think I would choose to balance all 8 together in parallel.