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Busbars for top balancing question.

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Sh4wzy

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Feb 6, 2022
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Hi all,
Quick question with regards to top balancing.
I have 4 Eve 280ah cells I'm about to build into a 12v pack for my camper build.
The cells came with only 4 busbars and at the time of ordering I didn't have the foresight to order extra for top balancing.
I do however have a length of copper c101 flat bar that measures 3 mm thick by 25 mm wide.
My plan is to use this to make 2 busbars for connecting the cells in parallel 1 for the positive side and one for the negative side, then use 2 X 10a bench power supplies to top balance the cells. (Thinking one supply clipped each side of the busbars)

So, would this copper be ok for the bus bars as my concern is that it may be to big??

Any help in this regard would be greatly appreciated.
Thanks in advance, Dave
 
Nothing magical happens during a parralel top balance.
I suggest you just charge one cell at a time.
Assuming they come ~50% charged it will take ~7 hours at 20 amps to fill each battery which is all a top balance really is.
You will need to make 10 awg cables to replace the wimpy ones that come with the PSUs.
You still probably won't get 20 amps though because of tiny differences in voltage between the PSUs.
Don't be tempted to turn up the voltage.
 
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For the low amperage that you're dealing with, that size copper bar will work fine. Clean the terminal surface and the copper. A thin layer of anti-oxidation paste may be in order since you're mating up copper to aluminum. I'm assuming that you have bare copper, not tinned copper.

If you have 100% confidence in your power supplies then connecting both may be appropriate. If there is any doubt, I would stick to just one.
 
Thanks Boondocker for your quick reply.
The power supplies are both identical units but I will double check the voltage outputs with my multimeter first to check equal output ??
 
HRTKD said:
For the low amperage that you're dealing with, that size copper bar will work fine. Clean the terminal surface and the copper. A thin layer of anti-oxidation paste may be in order since you're mating up copper to aluminum. I'm assuming that you have bare copper, not tinned copper.

If you have 100% confidence in your power supplies then connecting both may be appropriate. If there is any doubt, I would stick to just one.
Click to expand...

What anti-oxidation paste do you recommend?
 
John Frum said:
Nothing magical happens during a parralel top balance.
I suggest you just charge one cell at a time.
Assuming they come ~50% charge it will take ~7 hours at 20 amps to fill each battery which is all a top balance really is.
You will need to make 10 awg cables to replace the wimpy ones that come with the PSUs.
You still probably won't get 20 amps though because of tiny differences in voltage between the PSUs.
Don't be tempted to turn up the voltage.
Click to expand...
Sorry John, missed this before...
Reason for the busbars and parallel is I figured if I leave them for a couple of days they will fully even out?
 
chess-equality said:
What anti-oxidation paste do you recommend?
Click to expand...
I'm struggling to find an off the shelf product here in the UK but I'm really wanting to start my top balancing and battery build this weekend.
Can any body recommend anything that is readily available to get this weekend in the UK, or would be using the copper busbars without and anti oxidation paste be ok just for the top balance stage as I can probably get something on Monday?

Thanks again in advance, Dave
 
For the short term, an anti-oxidation treatment may not be necessary. When you take the cells apart after top balancing, pay very close attention to both contact surfaces to see how they were affected.
 
Sh4wzy said:
Sorry John, missed this before...
Reason for the busbars and parallel is I figured if I leave them for a couple of days they will fully even out?
Click to expand...
Paralleling batteries alone will even out the voltage but it won't do anything to even out the state of charge.
The reason this happens is the LFP voltage curve is extremely flat except at the very ends.

Each battery needs to be filled full, that is all top balance really means.
Parallel top balancing is just a means to an end.
Assuming you received your cells at shipping voltage ~50% state of charge it will take ~48 hours to do a parallel top balance.
I've seen so many people destroy their batteries before they ever get to use them doing a parallel top balance I strongly discourage it.

There are 4 main reasons for charging individually as opposed to parallel.
I can explain them if you are interested.
 
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John Frum said:
Paralleling batteries alone will even out the voltage but it won't do anything to even out the state of charge.
The reason this happens is the LFP voltage curve is extremely flat except at the very ends.

Each battery needs to be filled full, that is all top balance really means.
Parallel top balancing is just a means to an end.
Assuming you received your cells at shipping voltage ~50% state of charge it will take ~48 hours to do a parallel top balance.
I've seen so many people destroy their batteries before they ever get to use them doing a parallel top balance I strongly discourage it.

There are 4 main reasons for charging individually as opposed to parallel.
I can explain them if you are interested.
Click to expand...
Thanks John so much for your reply... I am very interest in learning more of the benefits of individual charging of the cells ??
 
Sh4wzy said:
Thanks John so much for your reply... I am very interest in learning more of the benefits of individual charging of the cells ??
Click to expand...
1. Temptation to turn up the voltage:
because of increasing system voltages and cell capacities plus the flatness of the charge curve...
People get temped to turn up the voltage because they don't see any progress.
Then all of a sudden they have overcharged and destroyed their cells.

I've seen this happen way too many times.

2. Paralleling your cells means they all get charged at a lower rate:
charging at lower rates deposits lithium on the SEI layer leaving reducing the cell's capacity

3. Internal short takes out all cells:
A cell internal short will destroy all the cells instead of just 1.

4. Mismatched SOC:
If the cells are not at a similar state of charge to begin with(cells can be at the same voltage and different states of charge)
1 or more of the cells will sit at a high state of charge while the other cells catch up.
Sitting full and being exposed to charge current is hard on those cells
 
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This article says 30%
www.iata.org

What to Know About How to Ship Lithium Batteries?

Lithium batteries are increasing in popularity, but despite restrictions you can safely ship lithium batteries by air. Here’s what to know about how to ship lithium batteries.
www.iata.org www.iata.org

Based on a SOC of 30%

280 amp hours * .7 depth of discharge * 4 cells / 20 amps = 39.2 hours to fill or ~10 hours each.
 
Sorry to borrow the thread but I'm in a similar situation with to few matched busbars for top balancing 8S lifePO4 batterybank. Is it possible to top balance 4 cells in parallel at a time then connect them together as one 8S top balanced pack?
 
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withaview2 said:
Sorry to borrow the thread but I'm in a similar situation with to few matched busbars for top balancing 8S lifePO4 batterybank. Is it possible to top balance 4 cells at a time then connect them together?
Click to expand...
Yes but better yet to just charge each cell individually to 3.65 volts and $n tail tail current.
As long as the charge process is consistent for each cell they are top balanced.
No magic occurs during parralel top balance.
It was just a means to an end that use to be convenient with lower capacity cells and is now the most common cause of destroyed cells.
 
John Frum said:
Yes but better yet to just charge each cell individually to 3.65 volts and $n tail tail current.
As long as the charge process is consistent for each cell they are top balanced.
No magic occurs during parralel top balance.
It was just a means to an end that use to be convenient with lower capacity cells and is now the most common cause of destroyed cells.
Click to expand...
Ok, thanks. Being a noob I'm unsure how to go about that. Is there any guide on how to do this using a power supply?
 
withaview2 said:
Ok, thanks. Being a noob I'm unsure how to go about that. Is there any guide on how to do this using a power supply?
Click to expand...

The Resources section of the forum has what you need.

diysolarforum.com

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
diysolarforum.com diysolarforum.com
 
withaview2 said:
Ok, thanks. Being a noob I'm unsure how to go about that. Is there any guide on how to do this using a power supply?
Click to expand...
I'm assuming you have a 10 amp bench power supply.

0. number each cell so that you can keep track of them.

1. make a new set of 10 awg leads for the power supply.
The ones they come with likely won't be thick enough for this application.
Use proper sized ring terminals to fit the power supply and the battery studs.

2. connect new leads to power supply.

3. set supply voltage to 3.65 volts and max current.

4. charge each cell individually until the current flow decreases to less than 1 amp.
do not adjust the voltage after attaching it the power supply to the cell.
Don't let the cells sit for days on end at 3.65 volts after they have finished charging.

5. let each cell sit for 48 hours and record the settled voltage.

6. when all cells are charged and the last one has finished its 48 hour settling period assemble the pack and commission it.
 
John Frum said:
I'm assuming you have a 10 amp bench power supply.

0. number each cell so that you can keep track of them.

1. make a new set of 10 awg leads for the power supply.
The ones they come with likely won't be thick enough for this application.
Use proper sized ring terminals to fit the power supply and the battery studs.

2. connect new leads to power supply.

3. set supply voltage to 3.65 volts and max current.

4. charge each cell individually until the current flow decreases to less than 1 amp.
do not adjust the voltage after attaching it the power supply to the cell.
Don't let the cells sit for days on end at 3.65 volts after they have finished charging.

5. let each cell sit for 48 hours and record the settled voltage.

6. when all cells are charged and the last one has finished its 48 hour settling period assemble the pack and commission it.
Click to expand...
Thanks for explaining the steps.

Yes. 10A 30V.

Will it cause damage to power supply using original leads or likely just not work?

Don't let the cells sit for days on end at 3.65 volts after they have finished charging.
Click to expand...

Does this mean it's not a good idea to top balance if I'm unsure on when I can get the system running?

Also. I read the following in the tutorial manual:

"Before hooking the power supply to the cells, set the power supply to .2C or less of the combined AH of the cells.
This will usually turn out to be the max current setting of the power supply"

Could you please explain this?
 
I see batteries and cells use interchangeably here. If I have rack batteries from same manufacture, bought together, do I need to “balance” them individually before I hook up the bank of them in parallel?
 
withaview2 said:
Will it cause damage to power supply using original leads or likely just not work?
Click to expand...
Current flow will likely be much less than 10 amps so the process will take much longer.
withaview2 said:
Does this mean it's not a good idea to top balance if I'm unsure on when I can get the system running?
Click to expand...
You should top balance just before you assemble the pack with BMS.
The you can draw the battery down to ~50% depth of discharge and leave it like that for monthes.
Leaving cells full for extended periods causes them to lose capacity faster than if the battery were cycling daily.
withaview2 said:
Also. I read the following in the tutorial manual:

"Before hooking the power supply to the cells, set the power supply to .2C or less of the combined AH of the cells.
This will usually turn out to be the max current setting of the power supply"

Could you please explain this?
Click to expand...
0.2c is a way to express charge current as a ratio of battery capacity.
For a 100 amp hour battery 0.2c = 20 amps.
For a 280 amp hour battery 0.2c = 56 amps.
 
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Danke said:
I see batteries and cells use interchangeably here.
Click to expand...
Edited my post to refer to cells.
Danke said:
If I have rack batteries from same manufacture, bought together, do I need to “balance” them individually before I hook up the bank of them in parallel?
Click to expand...
You should charge each battery full before you parallel them.
That stops excessive current flow between batteries when they are first paralleled and ensures they are at the same state of charge.
 
John Frum said:
Current flow will likely be much less than 10 amps so the process will take much longer.
Click to expand...
Ok. But faster balancing individual cells rather than all together?
You should top balance just before you assemble the pack with BMS.
The you can draw the battery down to ~50% depth of discharge and leave it like that for monthes.
Leaving cells full for extended periods causes them to lose capacity faster than if the battery were cycling daily.
Click to expand...
Then I will not balance untill about a couple months from now. Should I manage the cells in some way to protect them until full assembly?
0.2c is a way to express charge current as ratio of battery capacity.
For a 100 amp hour battery 0.2c = 20 amps.
For a 280 amp hour battery 0.2c = 56 amps.
Click to expand...
I see. So 56 amps regardless number of 280 Ah cells?
 
withaview2 said:
Ok. But faster balancing individual cells rather than all together?
Click to expand...
My method is for charging individual cells.
That is all that is required for top balance.
withaview2 said:
Then I will not balance untill about a couple months from now. Should I manage the cells in some way to protect them until full assembly?
Click to expand...
Give each cell a number and record its voltage.
You want to make sure you don't have 1 or more cells with excessive self discharge.
withaview2 said:
I see. So 56 amps regardless number of 280 Ah cells?
Click to expand...
My method is for charging individual cells.
With your bench power supply you are limited to 10 amps.

Lets guess that your cells are at 70% DOD
280 amp hours * .7 DOD = 196 amp hours
196 amp hours / 10 amps = 19.6 hours per cell.
If you did the old style parallel top balance it would take 19.6 hours * 8 cells = 156.8 hours.

I have been suggesting that you charge each cell individually at ~20 hours per cell.

Suggest you re-read my posts and the doco that @HRTKD and myself have written.
We have suggested two different alternatives to the classic parallel top balance.
Luckily you have time to get a good understanding of what top balance is and isn't before you proceed.
 
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