Almost everyone is charging their LFP wrong!

[PreppenWolf]

I love the OP giving a lecture and right in the beginning throws out "I did not top balanced my cells."

Nothing written after reading that line should be taken seriously.

 

[shvm]

I love the OP giving a lecture and right in the beginning throws out "I did not top balanced my cells."

Nothing written after reading that line should be taken seriously.

I love how you basically ignored the line saying I didn't had access to DC power supply and had to rely on BMS active balancing.
The vast majority of people's DIY batteries achieve their first top-balance from BMS active balancing. It is more than fine except it takes too much time. And it is not the main concern of the post either.

 

[justgary]

Absorb times should be no longer than what it takes for the current to taper down to 0.05 C.

This is completely dependent on initial charge current. My 48V 460 Ah battery (16S2P) is intentionally underpaneled because I don't need the batteries recharged in five hours. Three or four days to recharge is fine with me after I use the system on a weekend. My panels cannot produce 0.05C at all, so I certainly can't stop the charge at 0.05C or it would never charge at all.

If I had a system that could charge at 0.5C (230 Amps), I would definitely need to stop charging at 0.05C (23 Amps). I charge at about 3.4V per cell and float around 3.35V per cell, so the finish current is relatively unimportant.

My 12V 230Ah battery is so underpaneled (about 100W) that the BMS has registered one cycle in six months. It runs a small fan 24/7 but has plenty of reserve for me to use lighting, a water pump, and a small inverter when I am there. No issues so far.

 

[400bird]

The process is inherently self-balancing.

What? Umm, no it isn't.

Even for the recommended float value, it doesn't makes sense to recommend a value above 3.4 V/Cell. Anything above 3.38V is just overcharging.

You don't get to arbitrarily decide what is overcharging. See your own first post on this forum, where you referenced the manufacturer recommendation in your first post.

 

[PreppenWolf]

I love how you basically ignored the line saying I didn't had access to DC power supply and had to rely on BMS active balancing.
The vast majority of people's DIY batteries achieve their first top-balance from BMS active balancing. It is more than fine except it takes too much time. And it is not the main concern of the post either.

Using "the majority" of people cutting corners as a base for a post attempting to tell people how to do something right may not be the best approach.

 

[shvm]

You don't get to arbitrarily decide what is overcharging. See your own first post on this forum, where you referenced the manufacturer recommendation in your first post.

See, that is probably one of the many reasons people fail to understand what charging termination means exactly.

If you charge a LFP cell @ 3.65V and terminate charge when current tapers to 0.05 C and let the cell rest - it will never read 3.65V.

Using "the majority" of people cutting corners as a base for a post attempting to tell people how to do something right may not be the best approach.

There is no such thing as 'cutting corners' going with BMS active balancing. Granted, it is time intensive compared to top-balancing using a DC power supply. Using a BMS with 2 Amps Active balance current, balance will be achieved in like hours and will be just as good! In the meantime one has to be careful with charging voltages!

 

[shvm]

This is completely dependent on initial charge current. My 48V 460 Ah battery (16S2P) is intentionally underpaneled because I don't need the batteries recharged in five hours. Three or four days to recharge is fine with me after I use the system on a weekend. My panels cannot produce 0.05C at all, so I certainly can't stop the charge at 0.05C or it would never charge at all.

If I had a system that could charge at 0.5C (230 Amps), I would definitely need to stop charging at 0.05C (23 Amps). I charge at about 3.4V per cell and float around 3.35V per cell, so the finish current is relatively unimportant.

My 12V 230Ah battery is so underpaneled (about 100W) that the BMS has registered one cycle in six months. It runs a small fan 24/7 but has plenty of reserve for me to use lighting, a water pump, and a small inverter when I am there. No issues so far.

Charge termination current varies with Voltage.

Charging Marine Lithium Battery Banks | Nordkyn Design

nordkyndesign.com

Manufacturer-specified termination condition	3.65V @ 0.033C	3.65V @ 0.05C
Cell voltage (V)	Termination current (C)	Termination current (C)
3.370​	0.000​	0.000​
3.400​	0.004​	0.005​
3.425​	0.006​	0.010​
3.450​	0.009​	0.014​
3.475​	0.012​	0.019​
3.500​	0.015​	0.023​
3.525​	0.018​	0.028​
3.550​	0.021​	0.032​
3.575​	0.024​	0.037​
3.600​	0.027​	0.041​
3.625​	0.030​	0.046​
3.650​	0.033​	0.050​

In your case, 3.4V should be somewhere around 0.005 C not 0.05 C.

 

[justgary]

If you charge a LFP cell @ 3.65V and terminate charge when current tapers to 0.05 C and let the cell rest - it will never read 3.65V.

Yes, that is true. If I charge my LFP cell at 3.375V per cell, it will also never read 3.65V.

 

[Steve_S]

LMAO... Ohhh the Theorization, Conjecture & Postulation over documented & recorded facts is so phunny...

Bottom Line folks: It is YOUR Money, YOUR Risk & Liability and YOUR responsibility for the Consequences of actions you have taken to operate your gear.

Ask us for information & help and we will lead you to the proverbial water, then it is up to you to choose your next actions.

A final point. Many members are Hobbyists, many are actually within the trade & subsector doing this work and some have companies doing the deed around the globe. Not to forget, a few of us here have decades of engineering & other expertise some of which is DIRECTLY Related to this subject matter.

TERMINATION is to occur at the proverbial EndAmps / Tail Current.
100AH Battery has a TailCurrent of 5 Amps as teh IR increases at which point the cells ARE saturated.

 

[Partimewages]

@shv
Unless I missed it somewhere. What are your credentials? There's a lot of knowledge on this forum especially from people who have been here for a long time.

 

[justgary]

In your case, 3.4V should be somewhere around 0.005 C not 0.05 C.

The devil is always in the details. That table assumes that you are charging in a benign environment. If you are charging while the system is under load, it gets somewhat more difficult to simply state a stop current.

 

[shvm]

The devil is always in the details. That table assumes that you are charging in a benign environment. If you are charging while the system is under load, it gets somewhat more difficult to simply state a stop current.

Totally agree. What you said and that charge termination is the only way to correctly and safely charge LFP is exactly why my post heavily emphasizes on BMS to Charger communication.

 

[fafrd]

Active is moving power not burning it off. I tinkered with this through all of the testing phases & my nasty Thrash tests (pushing to the limit edges" and realized pretty quickly that starting Active balancing at a lower cell voltage actually takes the edge off. With the mix of cells I have, Used EV cells, Bulk, B & A grade, I got to see a bigger picture overall.

If I set to 3.400 to start Active, 2 of my packs will have close to 0.100 deviation BUT when Active starts @ 3.30 by the time we get to float they are 0.020-0.025 so it's a lot less work. I have No Idea WHY people keep thinking that Active wastes the energy, it doesn't, it moves it, with minimal loss.

I’ve left my active balancer connected 24/7 for over 6 months now and my pack is finally worry-free.

I’m a corner-case because I am bottom-balanced and discharge to 15-20% by 9pm (while never getting anywhere near to full charge).

My battery is so much bigger than maximum daily charge that risk of a runaway is non-existent and much greater concern is a drain-away (cell reaching 2.5V while pack still above 20%).

By leaving the active balancer on during the day I’m moving some energy I could avoid moving (with associated I^C losses I could avoid) but the hassle of rigging up controls to only turn on the balancer during overnight ‘rest’ from 9pm to 5am isn’t worth the trouble.

My battery goes to sleep at 9pm with all cells within 1% SOC of each other without fail, and that’s all I need.

 

[KITROBASKIN]

In spite of the click-bait(ey) 'most of you are wrong' title of this thread, other members have given us useful information. OP still seems a little too defensive to these eyes.

If the cell voltage difference while charging to 3.43V is less than/equal to .01V, is it 'good enough' in terms of the big picture (cell longevity balanced with capacity utilization)? Opinions welcome.

 

[Steve_S]

 

[42OhmsPA]

This thread motivated me to get my JBD connected to a PC... . Since I have been using SA for months I couldn't see individual cell data...
How do things look?
Anything glaringly wrong I should change?

 

[sunshine_eggo]

If the cell voltage difference while charging to 3.43V is less than/equal to .01V, is it 'good enough' in terms of the big picture (cell longevity balanced with capacity utilization)? Opinions welcome.

Yep.

 

[Warpspeed]

Yep +1

 

[Quattrohead]

Heck, if charged correctly I don't think balancing is required at all for months even. The process is inherently self-balancing.

What a crock of cow dung.

Even for the recommended float value, it doesn't makes sense to recommend a value above 3.4 V/Cell. Anything above 3.38V is just overcharging.

More manure.

I thought resting voltage at 50% was nearer to 3.3V? All my new grade A EVE cells arrived with 3.29V, which I understood was because they should be shipped / stored at about 50% SOC.

Proper fertilizer.

 

[KITROBASKIN]

Too soon. RIP Pee Wee.

From candlepowerforums member jz6342:

“This one hit hard. I was on Mr. Rueben's protective detail when he brought the Playhouse to Seattle. He was one of the nicest and hardest working celebrities I'd had the chance to work with. He always made sure the team was taken care of and was always moving. And he was truly funny. He will be missed?”

RIP Pewee Herman

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