Low priced LiFePO4 Batteries vs High priced

[newhaul]

Originally Posted by Phil_Fr17

And you tested the batteries without balancing them first?
A bit brutal, don't be surprised if you get imbalances afterwards if you haven't done it.

Not brutal at all I did that to verify the grade of my cells and the stating by seller that I had matched cells .
Then built bank and active balancer was used and I do an annual capacity test which does 2 things it balances the cells at bottom and top .

[Phil_Fr17]

Sorry, I'm French, so I sometimes have a few differences in expressions and turns of phrase.
Of course these are certainly not first-class cells, but very often people look at price before quality.
I also agree with the warning not to put them in parallel and to try to balance them before putting them into service.
And then we're surprised if they catch fire or malfunction...


And I was replying to Captain Rivet about the word ‘brutal’, perhaps misinterpreted, and especially to JoeLeng and his first post about how he had assembled cells without even balancing them from the top first, then checking that everything was good, before even testing the cells in parallel.
There was a risk from the outset, but with an unknown and certainly poor quality, it's a recipe for failure, especially if you put different cells in parallel.
Even an active balancer can't do everything in every case.

[CaptainRivet]

Originally Posted by newhaul

Not brutal at all I did that to verify the grade of my cells and the stating by seller that I had matched cells .
Then built bank and active balancer was used and I do an annual capacity test which does 2 things it balances the cells at bottom and top .

You can only balance either at top or bottom, both simultaneously is not possible. Even the best matched cells are not 100% identical so you have to decide on which end you do your balance, favourable is top balance and deviation at the bottom tells you how even in capacity your cells are. If you perform a bottom balance you destroy the top balance you achieved before.
What an annual capacity check does is you know your degregation of the cells, which cell is the weakest plus it calibrates SOC and also tests if your LCV and HCV work properly.
For this capacity check I raise the float voltage from 13.8V to 14.3V and float time to 1.5h. This has the effect that the HCV of BMS will cut charge when bank is really full at 3.63V and the long absorption give it really a top balance. But that 1.5h at 14.3V is needed because I have a 4P4S bank and the parallel cells only 100% even each other out in the upper knee and the active balancer can perfectly top balance.
If you have no parallel cells 30min at 14.4V is more then enough.

[newhaul]

Originally Posted by CaptainRivet

You can only balance either at top or bottom, both simultaneously is not possible. Even the best matched cells are not 100% identical so you have to decide on which end you do your balance, favourable is top balance and deviation at the bottom tells you how even in capacity your cells are. If you perform a bottom balance you destroy the top balance you achieved before.
What an annual capacity check does is you know your degregation of the cells, which cell is the weakest plus it calibrates SOC and also tests if your LCV and HCV work properly.
For this capacity check I raise the float voltage from 13.8V to 14.3V and float time to 1.5h. This has the effect that the HCV of BMS will cut charge when bank is really full at 3.63V and the long absorption give it really a top balance. But that 1.5h at 14.3V is needed because I have a 4P4S bank and the parallel cells only 100% even each other out in the upper knee and the active balancer can perfectly top balance.
If you have no parallel cells 30min at 14.4V is more then enough.

Great word salad
I do a bottom balance one time as part of my commissioning process to ensure maximum capacity when I charge my bank. After this one time I discharge to lvc annually and charge to a full 3.65for top balancing or 14.6 on my solar controller. After achieving this hvc point I reset voltage to 13.8 .
So now you are running lifepo4? Last time you posted what you had it was LTO.
Personally I don't care . Your boat your choice my boat my procedure. Same as I did for my customers installs. ( remember I'm retired now)

[CaptainRivet]

Originally Posted by newhaul

Great word salad
I do a bottom balance one time as part of my commissioning process to ensure maximum capacity when I charge my bank. After this one time I discharge to lvc annually and charge to a full 3.65for top balancing or 14.6 on my solar controller. After achieving this hvc point I reset voltage to 13.8 .
So now you are running lifepo4? Last time you posted what you had it was LTO.
Personally I don't care . Your boat your choice my boat my procedure. Same as I did for my customers installs. ( remember I'm retired now)

I run a 12V 1088AH Lifepo4 hybrid starter house in STB hull and a 12V 40AH LTO starter in the BB hull plus soon a 20AH LTO as buffer for the nav electronics at the navstation.

Well you cannot get max capacity with a bottom balance.
To get max capacity you need a top balance with a lower float voltage and long absorption time. Like this the balancer has a long time to really even them out and the longer absorption will saturate the cells with very low current over long periode so drop to rest voltage is smaller as the cell is really at 100% SOC.
With high float voltage and bottom balance you hammer in quickly and the higher current will make the weakest cell peak quickly into cut off voltage while rest of the pack may not even reach the knee depending on capacity differences of cells. This peaked cell is also not 100% full but 98-99%. Additionally the bank is operated from full to whatever capacity SoC you daily need, so a precises as possible full=top balance is favourable.
Only point when a bottom balance is better if you have a heavy cycled bank that reaches several times a day the LCV or close to it.
That's why it's recommended to do a top balance as a boats house bank are mostly oversized and normally operate full to normally max 50%SOC.

[wholybee]

Originally Posted by CaptainRivet

Well you cannot get max capacity with a bottom balance.

Yes, you will get max capacity with bottom balance. However, it is one or the other. You can't balance at both the top and the bottom. You pick one, and balance there.

In most applications, a top balance makes most sense, because you will try to never run the battery down to empty, and you try to fully charge it once in a while. But some applications, a battery will regularly be run empty, and rarely fully charged. In those applications a bottom balance works better.

But other than the application and how the battery is used, there isn't any advantage of one over the other.

[CaptainRivet]

Originally Posted by wholybee

Yes, you will get max capacity with bottom balance. However, it is one or the other. You can't balance at both the top and the bottom. You pick one, and balance there.

In most applications, a top balance makes most sense, because you will try to never run the battery down to empty, and you try to fully charge it once in a while. But some applications, a battery will regularly be run empty, and rarely fully charged. In those applications a bottom balance works better.

But other than the application and how the battery is used, there isn't any advantage of one over the other.

Nope a bottom balance can never achieve full capacity compared to a top balance. The difference is very small below 1% where a top balance achieves a higher total capacity. That's due to nature of having an upper charge limit which need to be saturated with low current to be fully saturated while on the bottom end there is no limit, the limit is set by the fact if you go below 2,5V you destroy the cell.
In real life forget the difference and what balance you choose we agree depends mainly how the bank is used. Due to fact that 99.9% of marine bank are oversized and operate full to max 50% SOC a top balance is the way to go.
I also don't know any drop in manufacturer who recommends to do a bottom balance, all recommend top balance mainly because their balancer can only top balance.

[s/v Jedi]

Ket me explain something about top balancing vs bottom balancing: you have to choose one and this choice is dictated by the charge/discharge regime.

For most boats house banks, you choose top balancing because the battery soc never goes low enough to reach the lower knee but often get fully charged and for many even daily fully charged.

For traction applications where maximum distance is key, you do a bottom balance because you want to be able to keep going as long as possible and battery capacity is tuned to the daily distance of driving.

[newhaul]

Originally Posted by CaptainRivet

I run a 12V 1088AH Lifepo4 hybrid starter house in STB hull and a 12V 40AH LTO starter in the BB hull plus soon a 20AH LTO as buffer for the nav electronics at the navstation.

Well you cannot get max capacity with a bottom balance.
To get max capacity you need a top balance with a lower float voltage and long absorption time. Like this the balancer has a long time to really even them out and the longer absorption will saturate the cells with very low current over long periode so drop to rest voltage is smaller as the cell is really at 100% SOC.
With high float voltage and bottom balance you hammer in quickly and the higher current will make the weakest cell peak quickly into cut off voltage while rest of the pack may not even reach the knee depending on capacity differences of cells. This peaked cell is also not 100% full but 98-99%. Additionally the bank is operated from full to whatever capacity SoC you daily need, so a precises as possible full=top balance is favourable.
Only point when a bottom balance is better if you have a heavy cycled bank that reaches several times a day the LCV or close to it.
That's why it's recommended to do a top balance as a boats house bank are mostly oversized and normally operate full to normally max 50%SOC.

Ok as to your bank on your vessel.
This is the first time I have seen you post your full Install in a single post.
Sounds like a great system for your vessel.


Now.
Did you even read my last post fully?

Please go back and read it all the way through.

Here I will make it easy for you .

"I do a bottom balance one time as part of my commissioning process to ensure maximum capacity when I charge my bank. After this one time I discharge to lvc annually and charge to a full 3.65for top balancing or 14.6 on my solar controller. After achieving this hvc point I reset voltage to 13.8 ."

When doing my initial commission I charge at a .1C rate to the HVC cutout point.
( yes my charging equipment is fully adjustable. )

Read that again I do the bottom ONE time . ONE time.
Upon initial commissioning.
No I don't use drop ins they are not reliable / repairable enough for me.
Their bms fails and its a big issue to fix .