Active energy transfer balancing

[john61ct]

This is just one of those words where clarity requires greater detail.

Like "love", pretty much useless without clarifying.

I am not personally advocating using "non-protective BMS" for balance-only devices, just pointing out the term is pretty widely used out there.

Switching topic

______
Anyone know if this is a quality balancer?

https://www.ebay.com/itm/192949118322

And where it can be obtained at lower cost?

Love the 5A rate independent of cell Vdelta.

Please spare me the "you don't need that" commentary. . .

 

[vreppeto]

Sounds like a crappy design to me, ...

I agree. But it's the only thing I could afford that does Broadband balancing instead of cell-to-adjacent-cell. I wanted to start cheap until I can figure out which ones are really worth spending money on. These caps are definitely junk. I just bought a whole new set to replace them with after two of them blew up.

 

[john61ct]

This seems reasonable, 2A rate should be plenty, independent of V delta

up to 24S

any voltage, so supports middle or bottom balancing not just when charging.

https://www.ebay.com/itm/283875420979

 

[vreppeto]

I just use a Biological Monitoring System (mark one eyeballs, brain, and hands).

Me too. For now. I do this with LFP cells since they tolerate overcharge to 4.2v before beginning to break down. (battery university) I don't try to charge more than 8 cells at a time until I get to know the pack. Start at 27.35 volts. When current drops to <100mv or so then I check again and raise the v-limit to 27.70 volts.
Check periodically for a cell that is going higher than the rest. If I find one I add a 2ohm 150w resistor to that cell and drop the current to 1.75a. I can add a resistor to 3 cells before I have to just switch to charging individual cells to create a top balance. This strategy eliminates the possibility of any single cell going higher than about 4 volts.

meta data - manual top balancing without a bms

 

[john61ct]

I do this with LFP cells since they tolerate overcharge to 4.2v before beginning to break down. (battery university)

That source is full of inaccuracies and over-generalisations. Excellent for beginners to learn the jargon though.

LFP should **never** be allowed past the max V spec'd by the maker.

That is already too high, if longevity is a goal.

Any charge profile that results in 3.33-3.35Vpc is as high as normal cycling ever should go.

There is **no reason** to go higher, you are only stressing the cells to no purpose.

If holding CV / Absorb there is no reason to go past 0.03C, really 0.05C is plenty especially if the setpoint is over 3.45V.

For occasional maintenance or benchmarking purposes, OK go a little higher no harm.

or if longevity isn't a concern, do what you like.

But just know it is possible to create an unquenchable fireball by overcharging any LI chemistry, even LFP.

 

[vreppeto]

I do this with LFP cells since they tolerate overcharge to 4.2v before beginning to break down. (battery university)

That source is full of inaccuracies and over-generalisations. Excellent for beginners to learn the jargon though.

LFP should **never** be allowed past the max V spec'd by the maker.

That is already too high, if longevity is a goal.

Any charge profile that results in 3.33-3.35Vpc is as high as normal cycling ever should go.

There is **no reason** to go higher, you are only stressing the cells to no purpose.

If holding CV / Absorb there is no reason to go past 0.03C, really 0.05C is plenty especially if the setpoint is over 3.45V.



For occasional maintenance or benchmarking purposes, OK go a little higher no harm.

or if longevity isn't a concern, do what you like.

But just know it is possible to create an unquenchable fireball by overcharging any LI chemistry, even LFP.

This is all news to me. The date on the article is July 2019. What is your source? "unquenchable fireball", with lfp at 4.2v !!?? "You are wrong and I am right" is not an argument that carries much weight.

 

[vreppeto]

I use a cc/cv power source for charging. In order to charge my cells I set the OCV and the current limit of the power supply then hit start. Because of resistance I have to set the OCV at 5v in order for the cells to charge at 3.65v. As soon as the charge voltage goes to 3.7v I lower the OCV to 3.65 and let them finish. I don't do this unless I am in a real hurry. My liitokala 32700 cells are not recommended for more than .5 c and I usually charge at .25c. I am working on a custom charger that will allow me to define and select each of these profiles.

 

[john61ct]

This is all news to me. The date on the article is July 2019. What is your source? "unquenchable fireball", with lfp at 4.2v !!??

Sorry no idea what statements you are questioning.

The fact that LFP can be set alight is obvious and well known, and once started yes very difficult to put out, dumping a huge pile of sand on top is best.

I said nothing about 4.2V specifically in that context, going that high for LFP is stupid for other reasons. As for a source for that, see your mfg, their max charge voltage as listed in the data sheets specify absolute maximum / minimum limits of acceptable ranges, they are not recommendations intended for normal functioning, operating conditions for day-to-day cycling.

As I stated, if longevity isn't a concern, do what you like.

 

[john61ct]

I use a cc/cv power source for charging. In order to charge my cells I set the OCV and the current limit of the power supply then hit start. Because of resistance I have to set the OCV at 5v in order for the cells to charge at 3.65v.

What you are doing is setting the voltage (and thus the current) so high as to skip the Bulk / CC stage completely and go straight to CV.

Yes that is faster, and in some cases sure we knowingly sacrifice longevity in order to charge as quickly as possible, for example going over 0.3-4C charge rate*

> I usually charge at .25c

That is great, even in cooler temps. When the cells are warm you can go faster without reducing life cycles.

The more usual, gentler strategy, is to set the voltage to your maximum CV setpoint (IMO no higher than 3.50V, at low current below 0.2C 3.45V is better) and

let the circuit voltage rise over time with SoC

you can in fact just terminate charging when CV is first reached, at a lower rate you are within a few percent of "working Full" anyway.

No fancy current-based termination algorithm is required, just a simple HVC cutoff.

But if you "want" a little time spent at Absorb / CV stage, no problem, just be sure to terminate the cycle before current trails any lower than say 0.1-2C

Obviously if your rate is already lower than that it becomes harder to avoid overcharging*

* I define overcharging as anything significantly reducing life cycles off the back end, not necessarily causing immediately detectable overt "damage"

 

[vreppeto]

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[vreppeto]

This is all news to me. The date on the article is July 2019. What is your source? "unquenchable fireball", with lfp at 4.2v !!??

Sorry no idea what statements you are questioning.

The fact that LFP can be set alight is obvious and well known, and once started yes very difficult to put out, dumping a huge pile of sand on top is best.

I said nothing about 4.2V specifically in that context, going that high for LFP is stupid for other reasons. As for a source for that, see your mfg, their max charge voltage as listed in the data sheets specify absolute maximum / minimum limits of acceptable ranges, they are not recommendations intended for normal functioning, operating conditions for day-to-day cycling.

As I stated, if longevity isn't a concern, do what you like.

Not very convincing. https://www.youtube.com/watch?v=Qzt9RZ0FQyM

 

[vreppeto]

Did you find this site yet? https://jkbms.com
or this one? http://www.enjpower.com/

 

[john61ct]

https://www.youtube.com/watch?v=Qzt9RZ0FQyM

Of course LFP is 1000x less likely to pose a fire risk, they are not perturbed by **many** events that cause other chemistries to explode.

Of course that does not mean excessive overcharging of LFP will not do the same.

Is that really the position you're taking? That LFP cannot burn if the charging regulation circuitry fails?

 

[vreppeto]

https://www.youtube.com/watch?v=Qzt9RZ0FQyM

Of course LFP is 1000x less likely to pose a fire risk, they are not perturbed by **many** events that cause other chemistries to explode.

Of course that does not mean excessive overcharging of LFP will not do the same.

Is that really the position you're taking? That LFP cannot burn if the charging regulation circuitry fails?

I know it seems okay to you to high jack someone else's thread for such an argument but it's not. If you want to argue about it start another thread. I imagine if you mention my name I will be notified. If you do then anyone who cares to join in the milieu is welcome. If you choose to do so you should copy this thread from the the post I made, your response and all the following remarks that are relevant ... or not.