Amount of cells? many or few

[flippy]

My definition of "stand alone" is that ... https://pt.aliexpress.com/item/4000529723243.html ... doesn't provide true "active charge" like that of a dc balance charger or analogy of a traditional 12v dc voltage regulator, alternator, etc (car BMS).

i am sorry, but you are not making any sense.

To say the aliexpress is an "active charge" BMS is a little misleading as it's more of a voltage equalizer ... more so than an "active Charger" between the p-groups. Similar comparison is the following equalizer analogy ...

its not misleading in the slightest. its just the standard chinglish auto translator. you have to re-convert into your head back into normal english yourself.

An analogy would be several small inter-connected fish pools in need of maintenance that slowly leak at different rates. The pools that leak the least will provide water to the pools leaking more thus hopefully maintaining all the pools at the same level ... wouldn't consider that an "active charge" compared to the pools being periodically "charged" by a spring to prevent them from all going empty.

that bms can be programmed to continously balance the pack if you wanted to. but you should not. you only balance during the end of the charging process and continue until fully balanced. that is also why you need high balacing current in the battery that is being made here.

... https://pt.aliexpress.com/item/4000529723243.html ... is certainly a welcome improvement over traditional discharge BMSs that for the most part are pathetic being more of a BPS at best than a BMS. That Ali BMS is an active leveling equalizer. By active i take that to mean that this Ali Smart BMS is constantly active :thumb: meaning it doesn't wait until the charged battery pack is close to FULL before balancing the p-groups via resistance discharge drain.

2 things to rectify in this:

1: "active leveling equalizer" is not a thing.
2: its not smart or "active", its programmable.

please dont see my comments are agressive, i am just to the point. i only want everyone to use the same terms so everyone talks about the same thing and does not confuse anyone else.

 

[MK2R]

Okay i am just going to get this concept as i understand it, correct me if i am wrong please, i want to learn.

If i have a string with 30cells, 3 of them selfdischarge, it will draw energy from all the other 27cells and bring all of them gradually to a lower voltage. but it should not affect the next paralell string, and therefor it creates an imbalance since they do not discharge in respect to each other.

And when you charge the pack without any sort of balance the bms will tell you when 1 string reaches target voltage and then cut off, even if the other strings haven't reached the same voltage.

The daly bms i have is supposed to do some balance at 4.18V, but just at 35mA. so even if it does top end balance, it will take a lot of time.

This kind of bms you are suggesting will give me the possibility to pick either a 13S or a 14S (or well, many different config). and then i need to plug it in somehow and program it, and there i could set different voltages of when the active balance process will occur? and if i understand it correctly since i can set a rather wide voltage range it could be used on either li-ion or lifepo4 cells


Ok a lot of interesting things, a lot to learn, but this is fun. i am so happy i turned to this forum, i have learned quiet a lot on top of my basic physics knowledge (over 10 years ago thou). Thanks so far to all of you! =)

 

[flippy]

you are correct.

the linked bms has presets for most chemistries so you would be 90% there just hitting the preset button.

generally it will start at 3,9V or so with a peak fo 2A of balacing current (dumping the high cells into the low cells) and will continue until the pack is balaced even if the charger is done.

 

[MK2R]

you are correct.

the linked bms has presets for most chemistries so you would be 90% there just hitting the preset button.

generally it will start at 3,9V or so with a peak fo 2A of balacing current (dumping the high cells into the low cells) and will continue until the pack is balaced even if the charger is done.

Okay! looks like i am at least starting to understand something.
Question: most bms system i see out there have a limit when it comes to charging. this bms have not even any spec for the charging process.
When you charge the pack with this bms when 1 string reaches (let's take your example voltage) 3.9V, the bms starts to dump voltage from that pack into the other strings meanwhile the charging process is ongoing at a peak of 2A. i immagine that the charging of the battery pack as a whole will never know what string is at what voltage, it will just see the pack as one unit that needs to be charged to whatever voltage (let's say 13S then it wants to charge it to 54.6V). so meanwhile that top most string is also being charging, it will both be charged and discharged (dumping voltage to the other strings) at the same time.

Is this correct understanding or will it shut off charging while it is discharging into the other string(s)?

 

[flippy]

The bms not care about. Charging. That is controlled by the charger, not the bms. The bms only intervenes if something goes wrong/out of spec.

If a group goes beyond 4.2v it will cut charging until its dropped to whatever voltage you have set. Usually 4.1v

 

[MK2R]

The bms not care about. Charging. That is controlled by the charger, not the bms. The bms only intervenes if something goes wrong/out of spec.

If a group goes beyond 4.2v it will cut charging until its dropped to whatever voltage you have set. Usually 4.1v

Okay, but charging a imbalanced pack without any kind of balancing at the top would be dangerous right, let's say a pack with 2 cells no bms at all ?. easy example of a simple 2S pack. one cell is 3V and the other one is 4V. 7V together and the charger is set at 8,4V, it wouldn't care that one cell is reaching 4,2V right? it would keep charging it becuase the other cell might only be at 3.3V (so just a total pack of 7.5V). or am i getting this wrong? :S

anyways. i am interested in that aliexpress active balance bms. Is that unit itself a recommendation, or is it just that type of bms that is recommended? sounds pretty smart to be able to pick many different type of series config and also be able to use it for both li-ion and lifepo4.

 

[flippy]

If a cell would get above 4.2v the bms cares and stops the charging. It does not limit current, it just hard stops incoming power and only allows outgoing power.

And yes. The bms i linked is rhe one you need. Just make sure you get the model with 2A balance current.

 

[MK2R]

If a cell would get above 4.2v the bms cares and stops the charging. It does not limit current, it just hard stops incoming power and only allows outgoing power.

And yes. The bms i linked is rhe one you need. Just make sure you get the model with 2A balance current.

thanks flippy!

Ok then i will actually order one of those bms units, 2A balance and they do connect to the phone via BT i assume, at least that is what it looked like when i looked up some reviews on youtube of that bms. I know it will take time for it to arrive, but since i got so many cells to test maybe it will arrive when i am done testing

 

[eMark]

1: "active leveling equalizer" is not a thing.
2: its not smart or "active", its programmable.

active leveling or equalizing of the p-group voltages at 2A is the same result as "active 2A balancing" of the p-groups of that Ali BT [Smart] BMS.

"Smart BMS" is often used in ES threads as is the recent "Smart Charger" thread ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=111412 ... "Selecting a Smart Charger".

Here are a few ES threads referencing a "smart" BMS ...

https://endless-sphere.com/forums/viewtopic.php?t=100323
https://endless-sphere.com/forums/viewtopic.php?t=105488
https://endless-sphere.com/forums/viewtopic.php?t=102860
https://endless-sphere.com/forums/viewtopic.php?t=102860

Smart BMS is marketing lingo, but it caught on as there are so many cheap (dumb) BMSs.
Smart programmable BMSs are not cheap or dumb (Smart BMS, Balance charger) ...
https://forum.esk8.news/t/monitoring-individual-cell-voltages-smart-bms-balance-charger/11023

even Aliexpress is guilty ... https://pt.aliexpress.com/item/32849172235.html ...
"Bluetooth smart bms with 100a constant current, suitable for 10s 36v 11s 12s 13s 48 lithium ion battery v 14s 15s with software"

please dont see my comments are agressive, i am just to the point. i only want everyone to use the same terms so everyone talks about the same thing and does not confuse anyone else.

So your point is well-taken that a so-called "smart" BT BMS is only as "smart" as the programmer. Don't mistake my similes as illogical or inaccurate, but rather as a fair comparison :thumb: ...

Simile: a figure of speech involving the comparison of one thing with another thing of a different kind, used to make a description more emphatic or vivid (e.g., the active balancing of interconnected pools of water, as is an active BT BMS ... OR ... a smart BT BMS, is only as smart as its programmer).

... but since i got so many cells to test maybe it will arrive when i am done testing

One way to test used cells is to make up some parallel groups of 25 (or 50) cells and let the voltages equalize (self-balance) for at least a day and record the p-group voltage. Then disassemble and check the individual cell voltages after a few hours and after a couple days to see how many cells are still at the same voltage as the recorded parallel group.

 

[fatty]

"Smart BMS" is often used in ES threads as is the recent "Smart Charger" thread ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=111412 ... "Selecting a Smart Charger".

The new poster in that thread mis-used "Smart".

 

[MK2R]

instead of starting a new thread i'll post a somewhat related, or maybe not related? question.

I know you can use a battery while it i being charged, like you use your phone etc.
But...
Heat? what happens in regards to heat? I am currently gathering information about solar-power into battery banks and from what i understand if you have a 2kwh battery with a theoretical 200w charging supply and you use an application meanwhile it is being charged of 400w you'll use 200w from the solar (charging source) and 200w from the battery.

but what happens to heat? will the battery be stressed the same way as it was supplying 200w, or will the battery develop the same heat as if it was supplying 400w?

or is the heat development of heat in that situation so little that it wouldn't matter and therefor no1 really talks about it

 

[flippy]

no, the power from the solar will not enter the battery so it will not get hot.

 

[MK2R]

no, the power from the solar will not enter the battery so it will not get hot.

Okay, is there any intelligent way that the system "knows" to not put the electricity into the batteries in this condition, or does it just follow the principle of using the way of least resistance (batteries have more resistance than the cable to the device using the power, so it goes to the device instead of the battery).

Or is this only possible to achive with some kind of a smart device like mttp unit etc

 

[flippy]

no, the power from the solar will not enter the battery so it will not get hot.

Okay, is there any intelligent way that the system "knows" to not put the electricity into the batteries in this condition, or does it just follow the principle of using the way of least resistance (batteries have more resistance than the cable to the device using the power, so it goes to the device instead of the battery).

Or is this only possible to achive with some kind of a smart device like mttp unit etc

its simple physics. energy flows to the lowest resistance point first. the battery has a higher resistnce so it does not go in there.
no intelligience required.

 

[MK2R]

no, the power from the solar will not enter the battery so it will not get hot.

Okay, is there any intelligent way that the system "knows" to not put the electricity into the batteries in this condition, or does it just follow the principle of using the way of least resistance (batteries have more resistance than the cable to the device using the power, so it goes to the device instead of the battery).

Or is this only possible to achive with some kind of a smart device like mttp unit etc

its simple physics. energy flows to the lowest resistance point first. the battery has a higher resistnce so it does not go in there.
no intelligience required.

Okay, i think i simply worry too much :lol:
today i got my charger. or well, not dedicated charger but a cc/cv unit with some digital display and bt connection. 0-80V and 0-5.1A (so at 80V 5,1A 408watt). i am going to supply it with a 60V 400w psu. and since i am not going to output those 408w, but instead like max 300w i assume it will be more than enough with a 400w psu.

does it matter if i charge my batteies with 0.5C or 0.2C. will a lower amp have any benefits? or is it just a con of more time to charge it?

 

[flippy]

the slower you charge the longer the battery lives.

 

[MK2R]

the slower you charge the longer the battery lives.

Is there any reddicilous slow speed that might be harmful? for example you charge a 500ah battery with just 1A current (so it would take 500 hours to fully charge it.

just as an example, why i am curious is that i have read somewhere (don't remember where) that u shouldn't charge your battery too long, but it might have been connected to a capacity testing, not sure thou, so i rather ask so i don't make wrong assumptions

 

[markz]

Sometimes its actually better to charge at 0.1A and have it take days on end to fully charge (if not weeks) but then practicality of life kicks in. So if you do not need to use the battery then it doesnt matter. If your vehicle or golf cart's battery has been drained, then its best to slow charge to try and save that battery, but if its an old battery then why not just spend $100+ on a new battery, but if your car is in for repairs then why not try to save old battery. Completely drained batteries need to be slow charged, the slower the better and safer, especially when it comes to lipo's, and any lithium battery. Drained to 0V or drained well below minimum voltage.

 

[flippy]

Is there any reddicilous slow speed that might be harmful? for example you charge a 500ah battery with just 1A current (so it would take 500 hours to fully charge it.
just as an example, why i am curious is that i have read somewhere (don't remember where) that u shouldn't charge your battery too long, but it might have been connected to a capacity testing, not sure thou, so i rather ask so i don't make wrong assumptions

can you fill a bucket too slow?

in short: no.

 

[MK2R]

Okay, then i shouldn't worry when i try my charger out (for example i put the settings 4.2V and 0.2A to test charge one of my FST cells and see what happens).

 

[flippy]

just charge as fast as you actually -need- to, not how fast you -can- charge.

 

[markz]

Be careful not to set it and forget it, the charger might keep charging your battery well beyond 4.20V before you check in on it and realize whats happened. A good quality charger is nice to have in that regard, the iChargers are good, but you pay for what you get unlike a cheap $20 Hobbyking RC charger.

 

[flippy]

Be careful not to set it and forget it, the charger might keep charging your battery well beyond 4.20V before you check in on it and realize whats happened.

stop saying that. if you set the voltage it will never get higher. period. end of story.

 

[MK2R]

Before i connect this to my cc/cv unit i wonder, is this correct? I just copied what was on the picture and i checked that the ground cable is the correct one. Does blue/brown order even matter?

https://www.allaboutcircuits.com/textbook/reference/chpt-2/wiring-color-codes-infographic/
Since i am in EU, as i understand it brown is "Live", blue is "Neutral" and the green one is ground


Just checked it: everything works just fine, just need to find a safe way to test-charge a lithium cell. will get cellholder with cords in a bit so i might have to wait until that thou.

 

[MK2R]

Well i am not going to lie, this site actually got me kinda interested in making my own EV bike, i mean i already have a sportbike (a suzuki gsxr 750 k8), and i have 2 more chassis for 125cc 2stroke bikes and one of those chassis have a totally screwed engine so maybe a donor bike for an ev project.

This is a question related to the actuall topic, "amount of cells".

I am looking at brand new cells, both 18650 and 21700/20700 cells. some cells are rated at 18-30A and some are rated to 7-ish A.

scenario:
desired max output 3kw
cell type 1 (sanyo 18650 1200mah 18A output): 61cells = 263mAh, 1098A output (~4kw)
cell type 2 (LG 21700 4850mah 7.3A output) : 150cells = 2619mAh, 1095A output (~4kw)

obviously the amount of cells needed to get the same output means that the LG cells will last 10 times as long. but the price difference is a lot in the different scenarios.

if you scale up the sanyo to the same amount of storage, the sanyo are still cheaper but they get abundant.

600 sanyo: 2592mAh (10800A output, ~39kw) 43g each (25,8kg pack)
150 LG : 2619mAh (1095A output, ~4kw) 68g each (10,2kg pack)

so if we just look at amount of cells in the 2 scenarios
1: comparing same nominal output
2: comparing same capacity
What would matter the most in this case? would the 600 sanyo be performing better at 3kw than the 150 lg at 3kw? same mah rating but a huge difference in maximal output current.

how would 61 sanyo at 3kw vs 150 lg at 3kw perform? each pack would have the same max nominal output perform similar at a short time (until the sanyo run out of juice...) or would the big difference in capacity matter a lot in this case even if they are rated to perform a similar output?

Many questions i know, but it's been some thoughts that's been bugging me all night now