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Top balancing my new lifepo4 cells

Tasemu

Tasemu

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Joined
Dec 23, 2020
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41
Hi all!

Today I received my new 4x lifepo4 280ah cells. I live on a boat and have 2x victron 100/30 mppt solar controllers and a sterling 20a battery charger. I want to top balance my cells from the generator and maybe the solar (its winter in the UK). I cannot really afford a bench power supply with a decent amp rating so was wondering if I could combine what I have with a buck converter to achieve a 3.65v top balance for my cells. Hoping to get some advice, thanks in advance for anything. :)
 
Download the PDF and thoroughly read:

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

Step 1 is to build the 4S battery with the BMS and series charge it until the BMS protection kicks in. This helps reduce balance time dramatically. You may also find that you don't need to top balance.

The recommended 30V/10A charger is about $US60 - easier and probably not much more expensive than trying to cobble something together.
 
Thanks for the help! I got my daly bms all hooked up and activated. However it has now appeared to go to sleep and bluetooth is not working. Does anyone know how to wake these up? TIA :)

P.S: Bench power supply is in the mail!
 
Top balancing is going well I think. Wish I had a grid option though, gonna be a fair few hours on the generator.

1611398566146.png
 
Hi , so by the look of it your going to series charge until cutout then disconnect and then parallel them then finish with top balancing ?
 
MisterSandals said:
And is that a straw in your Stella?

The internet never forgets. Just sayin...
Click to expand...
Haha nah, its just the light from the door crack.

Kesa32 said:
Hi , so by the look of it your going to series charge until cutout then disconnect and then parallel them then finish with top balancing ?
Click to expand...
That's the plan, however the cells are looking like they're staying in balance so i may not need to parallel
 
And those alligator clip connections are unlikely to give your charger accurate feedback so be careful or completely trust your BMS (not recommended for top balancing).

Stuff happens you know. Just do a forum search for bloated cells.
 
I've hit the high voltage cut-off in series, just reconfigured to parallel and accidently got a big bang when i shorted a cell. all appears to be charging now though. Not sure how long the parallel charge will take. Really not looking forward to have to capacity test these cells and charge from 0 again....
 
Tasemu said:
Really not looking forward to have to capacity test these cells and charge from 0 again....
Click to expand...
From what you’ve written so far, it sounds like all your cells are decent. I would try just putting them to use after you top balance.
And THEN IF you suspect there is a problem, AND you have a course of action (still in return period), perform capacity tests to make your return case.

As you’ve seen, accidents happen and cells get ruined when working with them. Stress testing is probably the most likely time to damage cells.

Some people need the “feel good about your purchase” stress test numbers. Just be sure to weigh the risks as well as time and effort.
 
MisterSandals said:
From what you’ve written so far, it sounds like all your cells are decent. I would try just putting them to use after you top balance.
And THEN IF you suspect there is a problem, AND you have a course of action (still in return period), perform capacity tests to make your return case.

As you’ve seen, accidents happen and cells get ruined when working with them. Stress testing is probably the most likely time to damage cells.

Some people need the “feel good about your purchase” stress test numbers. Just be sure to weigh the risks as well as time and effort.
Click to expand...
I've rearranged my cells into parallel but do not have enough bus bars, i've used a spare set of wires to connect the cells but 2 of them are at 3.36 and the other 2 are at 3.41 now. Should I expect these to level out? Power supply is currently supplying power at 3.6v (can only charge to 1 decimal place) and 3 amps (not sure why ampage is so low).
 
Are the charge leads connected to opposite ends of the parallel pack? + on one end, - on the other.

If your bus bar wires are NOT hot, they should be sufficient.
 
Batteries are almost fully top balanced at 3.45v in parallel. I have another question though. My Victron Smart-Shunt is not arriving for another week. Is it a bad idea to install this battery as-is for now and then just charge it up to bms cut-off again before installing the shunt?

Thanks in advance!
 
No. The smart-shunt is just a monitor to relate SoC to net current flow. Using the battery with a BMS protecting the cells is what's needed. The shunt, while highly useful, is optional.
 
snoobler said:
No. The smart-shunt is just a monitor to relate SoC to net current flow. Using the battery with a BMS protecting the cells is what's needed. The shunt, while highly useful, is optional.
Click to expand...
Excellent, I've got that all set. Just wanted to make sure it wouldn't cause issues when it came time to install the shunt.
 
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