GUIDE to properly Top-Balance and Charge a LFP Battery: Part 1

[shvm]

That depends on real world experience, level of common sense and lots of other things...

I have read the forum's consensus on how it approaches LFP charging and balancing.

I can immediately recognise why it's wrong because I have applied both to my very own battery and witnessed the correct behaviour. That's common sense according to me.
It's better because it can easily tested to be *better* in the real world testing also. I'm not making this up. This is also what every LFP cell's datasheet says.

 

[shvm]

Exactly this. There are some very bright people on here who have invested in learning about this that I can count on because of their real life experience applying that knowledge. I think I will follow their lead.

Now, if a newbie comes on here and lays out their creds, say from the manufacturing or testing side of things, I'm all ears.

OPEN CHALLENGE to anyone:

Make a simple video comparing the behaviour shown by cycling 4S LFP battery following both, the consensus on this forum and the proper way according to Nordkyn. Never was my ingenuity in the first place.

The differences alone will speak for themselves. As simple as that.
Why take my words for anything when it can be readily tested and observed to be true in real world experiments.

As of now, there's not a single such video in existence as I know of comparing those two.

 

[upnorthandpersonal]

Make a simple video comparing the behaviour shown by cycling 4S LFP battery following both, the consensus on this forum and the proper way according to Nordkyn. Never was my ingenuity in the first place.

You mean in a controlled environment, disconnected from an actual solar panel set-up?
3.0V - 3.5V - 3.0V, with solar, in real world conditions and an array scaled accordingly, with a battery aiming to provide days of autonomy in an off-grid application? I've been doing that with mine for close to five years now. What exactly would be 'better' by using a 'standard' cycle method as per Nordkyn when one doesn't even have the solar power available to do a 0.5C charge? (see my post #16 as well).

 

[shvm]

You mean in a controlled environment, disconnected from an actual solar panel set-up?
3.0V - 3.5V - 3.0V, with solar, in real world conditions and an array scaled accordingly, with a battery aiming to provide days of autonomy in an off-grid application? I've been doing that with mine for close to five years now. What exactly would be 'better' by using a 'standard' cycle method as per Nordkyn when one doesn't even have the solar power available to do a 0.5C charge? (see my post #16 as well).

0.05 C cut off is the entire point of this thread. Not 0.5 C charge.

 

[Skypower]

You mean in a controlled environment, disconnected from an actual solar panel set-up?
3.0V - 3.5V - 3.0V, with solar, in real world conditions and an array scaled accordingly, with a battery aiming to provide days of autonomy in an off-grid application? I've been doing that with mine for close to five years now. What exactly would be 'better' by using a 'standard' cycle method as per Nordkyn when one doesn't even have the solar power available to do a 0.5C charge? (see my post #16 as well).

You beat me to it. Real world vs lab

 

[upnorthandpersonal]

0.05 C cut off is the entire point of this thread. Not 0.5 C charge.

0.05C cut-off at what, 3.5V? There is no point going to 3.65V. Also, 0.05C cut-off after charging at what power? (see #16 - the voltage you reach at battery depends on the charge current you can supply, hence my 0.5C remark). Also, suppose you're at 3.65V (which you shouldn't), and you cut off at 0.05C: who's to say it wasn't a cloud?

 

[shvm]

GUIDE to properly Top-Balance and Charge a LFP Battery: Part 1

Do you know that LFPs need to be balanced every few months and not at every charge cycle? OR Are you aware that setting float voltage of your LFP battery above 3.37V/Cell is overcharging it and harming its potential lifespan and causing cell imbalance? Chances are extremely high that you don't...

diysolarforum.com

@upnorthandpersonal

Are you aware of this chart and what it means?
A simple YES or NO.

 

[SeaGal]

I have read the forum's consensus on how it approaches LFP charging and balancing.

I can immediately recognise why it's wrong because I have applied both to my very own battery and witnessed the correct behaviour. That's common sense according to me.
It's better because it can easily tested to be *better* in the real world testing also. I'm not making this up. This is also what every LFP cell's datasheet says.

... is that you, my @Solarcabin Channel friend?

 

[ghostwriter66]

ME = "Hey whatever most of us are doing seems to work - there's no fire -- good enough for me"

Self-appointed "LFP Expert" - OMG your using a 2/0 instead of 3/0, your torqueing your batteries at 8 n/m not 8.5, your charging them to 3.65 instead of 3.6255, you did not compress your batteries - you did not grind the terminal base down to a shining marble finish before connecting busbar, YOU realize that you have taken at least 2 days off the lifespan of a 15 year battery!!!"

 

[webbbn]

OPEN CHALLENGE to anyone:

Make a simple video comparing the behaviour shown by cycling 4S LFP battery following both, the consensus on this forum and the proper way according to Nordkyn. Never was my ingenuity in the first place.

The differences alone will speak for themselves. As simple as that.
Why take my words for anything when it can be readily tested and observed to be true in real world experiments.

Specifically what difference in "behaviour" should one be looking for? Not that I have any 4S batteries to test with, but I don't see what problem you're trying to solve.

 

[Q-Dog]

The manufacturer of my last drop-ins says to float at 3.45v per cell, so I might do that. Currently set lower. But I Don't really care, My system rarely floats.

 

[upnorthandpersonal]

Are you aware of this chart and what it means?
A simple YES or NO.

Yes. Do you understand the graph in my post #16? Do you also understand that the load of a house should still be powered by solar when available even when the battery is full? Do you understand that it's easier to just stop charging when you're at 3.5V and not worry about any tail current at that point at all?

 

[shvm]

Specifically what difference in "behaviour" should one be looking for? Not that I have any 4S batteries to test with, but I don't see what problem you're trying to solve.

Very good question.

You will see that there's no need for any balancing for months with the proper method. That's why it's correct and the consensus with 'balance above 3.45 V when the Cells are above the knee' or whatever is wrong.

The manufacturer of my last drop-ins says to float at 3.45v per cell, so I do that. Don't really care, My system rarely floats.

If it is LFP, there is no point floating above 3.37 V/Cell.

 

[webbbn]

The manufacturer of my last drop-ins says to float at 3.45v per cell, so I do that. Don't really care, My system rarely floats.

If my batteries start floating, I'll have more important concerns than charge voltage!

 

[upnorthandpersonal]

You will see that there's no need for any balancing for months with the proper method. That's why it's correct and the consensus with 'balance above 3.45 V when the Cells are above the knee' or whatever is wrong.

I also don't have a need to balance for months - I never get a full battery in winter. In summer, the pack is almost full every day. If you just have a BMS with active balancer, putting it at 3.5V or so won't do any harm whether it needs a balance or not. And it's a lot easier to implement compared to dealing with tail currents (who needs to do this: the BMS? So you need a BMS that limits the current. Or to tell the controller what, to stop putting out power? But what about my loads then?).

 

[Alarchist]

As I see it, the crux of @shvm's point is that we should not ignore the data sheets hard limit for tail current.

I think most would probably see as @upnorthandpersonal pointed to, roughly using a minimum of 3.0V and maximum 3.5V discharge and charge voltages will most likely also improve longevity.

I.E. Focusing on just the absorption voltage whilst ignoring tail current or vice versa, we'd only see one of the two important dimensions to charging LFP, unless the wisdom from experience is that tail current is less important than the data sheets point to?

I do wonder how a parallel top balance below the data sheets recommended tail current (albeit maybe only a few times a year) really impacts their longevity, seeing as so many people seem to do it?

 

[shvm]

Yes. Do you understand the graph in my post #16? Do you also understand that the load of a house should still be powered by solar when available even when the battery is full? Do you understand that it's easier to just stop charging when you're at 3.5V and not worry about any tail current at that point at all?

The tail current for charging at 3.5V is around 0.02 C.

I also don't have a need to balance for months - I never get a full battery in winter. In summer, the pack is almost full every day. If you just have a BMS with active balancer, putting it at 3.5V or so won't do any harm whether it needs a balance or not. And it's a lot easier to implement compared to dealing with tail currents (who needs to do this: the BMS? To tell the controller what, to stop putting out power? But what about my loads then?).

That's not what I meant to say.
Even with full charge and discharge cycles everyday for a month, you won't need to balance. That's why the emphasis on properly understanding on what the proper Charge models says and what it doesn't in the first place.

Unless one experiences it first hand, how is anyone supposed to realise why it is better??

This discussion is pointless and will continue that way without experiments.

Good night everyone

 

[scubadoo]

Despite all the theories, papers and forum posts read over many years our battery has never required balancing since the original careful top balance.

In the meantime we will continue to use our 9 year old 300Ah 4 cell Sinopoly LiFePO4 battery to both power the house and start our motorhome 3.9l turbo diesel Fuso Canter truck engine often multiple times daily during our full-time travels.

I occasionally check the cell balances and practice a little tweaking, but apart from any phycological satisfaction it achieves absolutely nothing. It certainly can have no effect on battery capacity.
Pulling any 100mV deviant cell into line requires no more than a few seconds and mWh at 30A.

No standard BMS unit or balancing involved here. The 740A peak engine start current would be tricky.
14.1V maximum from any charge source, 20% SOC alarm and 12.5V Victron BatteryProtect disconnect. Never triggered.

With just a 5% capacity loss over 9 years at the last November annual C/10 test we must be doing something right despite all the doomsayers.
A recent push to 14.5V from our 14.1V always 100% SOC took less than 30 seconds at 30A.
"Float" is 13.40V but that is never maintained for long. We use our battery.


Click to enlarge.

 

[JJJJ]

We have a number of very talented and experienced members on this forum. @upnorthandpersonal has made some amazing contributions to this forum. He has an amazing understanding of the technology and his understanding of the electronics behind the Bms is second to none.

I top balanced my first three battery packs. I will be using an active balancer for this next one.

 

[upnorthandpersonal]

how is anyone supposed to realise why it is better??

Again, define 'better'? To implement tail current, you need some kind of communication with your charge controllers to stop putting in power, or a BMS that can limit current. Neither which are a good solution: find me a BMS that does this, or tell me why I should right away involve my battery to power the load when solar (and the charge controller) can continue to power my load, but are told by the BMS to stop.

Tail current is great when you a) test batteries, or b) have an application that is ideal in the sense that charging the battery and discharging the battery happens in sync with available/non available energy. When in practice, I have a fluctuating source of power from which I want to capture the most amount as possible, and just stopping at 3.5V (or 3.55V) charging voltage will do just that without any balancing issues (again, five years in with my packs if you want real world experience). Also, again, imagine you're at 3.5V (due to a very quick burst of incoming solar) and you have a cloud come over which makes your current drop. How do you distinguish that from meeting the tail current?