It’s completely offtopic man 
I could say the same thing about your message but HEy My topic I say its not off.
thanks @kug3lis you’ve made my day 
On topic… leaving cells at 4.2V at top charge without a charger connected degrades the battery. Period!
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Something like this:
Oh really? Tesla recommends charging to 90% they, they clearly know nothing about batteries.
That’s just an example of all the bullshit you’re spreading, i think you should take your own recommendation and go read some more.
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Im not on anyone’s side but he did cover the tesla point in an earlier post
Yes, everyone tells tips and tricks about charging battery but everyone allows you to charge battery to 100% same as your phone same as your laptop all of them charge to 4.2V So I don’t know what kind of “bullshit” I spread 
If it is so good why they don’t enforce it
P.S. To not get on point about end voltage but general used batteries charge to 4.2V Some newer phones uses newer chemistry which even charges to 4.3 and etc I said it as example.
Not everyone 10char
Goodnight guys, @moderators You can close and hide this topic if ya like or if someone else would like that.
And Smartphone batteries are known to last forever 
.
And Industry tries to make money. Everything that lasts forever doesn’t create money in the industries wallets.
And of course not many would buy a battery with charger that has 20% less capacity because they only charge to 4.0V.
@Kug3lis Didn’t you read the stuff you posted yourself? Especially the last table.
But finally we shouldn’t really care. Even 300 cycles with a 30km range battery (e.g 10S4P) will give us something like 7500 km (capacity becomes lower with each cycle). And that is under worst conditions.
Simple rule (or advice, tip, recommendation, hint) should be to not keep it fully charged when you store the board.
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Ish…
There is no such thing as a pure cc charger. They all have a voltage limit. As you stated, a 42V 2A charger is in fact a cc/cv charger. It will charge 2A at any voltage under 42V. It cannot charger to a voltage above 42V. As the voltage of the battery approaches 42V, the current pushed through it will decline per the following… DV = Vc - Vb = I * Ri Vc = Charger output voltage Vb = no load Vbatt I = charging current Ri = Battery Internal resistance
The difference between a power supply and a charger is the defined constant current provided by a charger and an end of charge current. A power supply may be rated for 10A but does not actually regulate to 10A, it may simply have a fuse that will blow at 10A.
For power supplies, they define a max load and it’s your job to stay under it. For a charger, they define max power output, regardless of your power needs. This is obviously not true for all supplies but is generally true for cheap ones.
Enough on that tangent…
In order for this to be true, the charger needs to be capable of charging at a higher voltage as dictated by the equation above. There is no escaping physics I’m afraid.
Ish… Most BMSs can only turn on/off charging. So if you were charging at 2A, and the BMS saw a cell reach 4.2V. It would turn off charging for all cells altogether while it enables the discharge resistor for the specific cell. The way it works is that above a specific voltage for each cell, the balancing resistor will get enabled, this could be anywhere between 3.9V-4.1V and is unrelated to the overall charging function. The resistor can only dissipate so much power, lets say 150mA. So if your battery is charging at 2A and balancing is enabled for 1 cell, then that specific cell is charging at 1.85A while the others are charging at 2A. This goes great with CC/CV chargers as the overall current approaches zero and then the balance resistor can take all if not even discharge an over charged cell.
Now, the second part of the BMS is turning on/off charge/discharge. In my experience, a good BMS will be able to take the input of all cells as a group as well as all cells individually and decide to turn charging on/off based on that. If a single cell reaches 4.2V, while the others are at 4V, charging should stop until some balance threshold is achieved.
For example in my BMS, that threshold is 100mV/50mV. All cells need to be within 100mV regardless of the voltage for charging to be enabled and within 50mV of each other if a cell is above 4.1V. This is not normal from a cheap BMS, I spec’ed out my own and got it from Texas Instruments but most good BMSs will have a threshold of like 150mV.
Other than that, the BMS will have a turn off and turn on voltage threshold for charging. Eg, if cell is above 4.2V, turn off. Turn on if cell is below 4.05V. This means that your cells will not be charging for eternity. This goes hand in hand with the low current limit on CC/CV chargers. CC/CV chargers will stop charging if they cannot charge faster than 0.xxA. Mine is 0.1A. So there is some redundancy. If my charger is faulty and never stops charging then the BMS will tell it to stop unless the battery actually needs charging. Same thing if my Bms is faulty, then the Charger should stop itself if charging too slow. You would need two failures for it to even become a problem. That is a main theme with power systems, be redundant in your protection in different places. Some may think it’s stupid until their shit’s on fire.
I’m not sure I’m following the logic here. If you need more explanation beyond what is above. Let me know.
Errr. No. Depends on the BMS but most good BMS do monitor individual voltages. I’ve tested this on several of them. So you’re definitely wrong on this one.
You are correct. He is wrong. Simple. He is just being rude and condescending. I would ignore.
This… LOL. Seems he knows how to copy/paste but didn’t pass the reading comprehension test.
@Ackmaniac, a little secret though… Those tables are inflated. A lot. Based on my own research.
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No, for the Moment i am good!
Thank you very much for your time and effort to erase some misleading Information! Nice to have you on board!
Do you have own tables? 
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This. Thanks for the lengthy comment, very spot on.
That being said, depending on the BMS, usually cheap ones don’t balance before a cell reaches a certain voltage. The balancing act also can happen if the charger is not plugged in.
I’ve talked to BesTech and they confirmed their BMS will balance even if charger is not plugged in. However, because the balance only happens when a cell goes above a certain value, it’s not a good idea to only charge to let’s say 80% for many many cycles. While this would increase the battery life (I do top up many times and unplug at 80% because I know I don’t need more), it also means the balancing act, if required, cannot begin because the cells are below the threshold.
As far as I know, it’s best to not charge to 100% unless you need it and you are about to use it… but at the same time, if you kept your battery between 80%-20% for many cycles, it’s good to do a 100% charge every now and then so that the BMS can re-balance the pack if needed.
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Can’t share them shamefully since they are work related.
Do you know at what voltage they start balancing?
It is okay to not balance as long as you’re not abusing the cells. In fact, it is better for the cells not to be balanced every cycle. The reasoning is that when you balance, your cells spend hours near 4.2V which can be detrimental for them while an unbalanced charge can be done within 30mins of the cells hitting 4.2V.
Also balancing isn’t needed that often. I usually go 20-30 cycles between balance charging and my cells will be within 10mV. I do check them after every cycle though. One thing balancing does is that it protects you when a cell goes bad, so if a particular cell goes bad and you don’t balance for another 20-30 cycles, things could get really bad. I don’t know if you saw my post about the battery that was perfectly balanced when charged but definitely had a bad cell within the group. I’ll post a link below…
Yep! Thats the best practice. Also don’t forget to check voltages yourself after every season. Both fully charged and discharged. It can save your butt.
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I think @whitepony would Support this! He is mostly running without bms because you dont really Need one with Quality cells in a well designed board (enough p rows for the application).
When you have several boards and/or work often with cells, it seems to be a good option to use balance charger instead of BMS.
Balance chargers allow to tune the termination voltage and balance cells even at 80%. You can also decide if you want to balance cells of not, you can adjust the input current depending on your needs and time.
Finally they provide several additional features like IR measurment and multiple checks for safe charging.
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This is what I have from Bestech themselves:
3)Once the voltage of a single cell reach 4.20V+/0.025V, the balancing start. After battery pack is fully charged, PCM will detect each cell’s voltage and trim higher voltage down until other cells reach the same voltage level.
And
Once the voltage of a single cell reach balance voltage 4.20V+/0.025V, the balancing start. It no need to leave the charger.
These are simple bms modules so one balancing module inside the bms doesn’t talk to the other, meaning there is no way to start balancing before a cell reaches 4.2v. If you charge a pack and at one point a cell (A) charges faster (or it wasn’t as discharged as the other to begin with) and reaches let’s say 3.8v while another (B) is at 3.7v, the bms wouldn’t know that A cell is higher than the B one. However, as cell A reaches 4.2v, the B one is still at 4.1v. So the charger keeps charging, but the BMS is seeing cell A at 4.2v already and starts discharging it via the resistor, essentially keeping it at 4.2v. At the same time cell B is still charging and at some point it reaches 4.2v as well. Cell A was kept in check and didn’t go beyond 4.2 while cell B was allowed to catch up. When the charging act finishes, both are at 4.2v, so balanced.
As far as I understand it’s a simple process: if any cells reach 4.2v, they are kept there as lower ones catch up. This is why a 100% charge is needed every now and then, otherwise there is nothing to balance them. It’s also why if you build a pack and mismatch voltages across the cells/P groups, the first charge will be tricky: either the bms can hold the higher ones at 4.2v while the others catch up or (if the balancing current is not high enough and the mismatch is too big), it will stop charging because the already high voltage cells cannot be kept at 4.2 due to more current going into them compared to what the resistor can eliminate.
The important thing is that since there is no communication to find out what voltage the other cells have, they can’t be balanced as their voltage goes up. You would reduce the time needed to balance if you start as soon as the battery is being charged: check all voltages across the cells and if you find a difference, slow down the higher ones from the first second the pack started charging and allow the lower ones catch up… but because there is no communication like that in a simple bms, it literally just waits until a cell is at 4.2v and keeps it there until the others are catching up.
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That being said, I checked my 10s4p pack (30Q) and after 400 miles on it, it never was unbalanced. I check when discharged, to see if they drifted during discharge phase, and at the end of a 80% charge, to see if they charge at the same rate. And since they are quality cells, they seem to degrade at similar rates, essentially keeping the balance perfect.
I also check at 100% just to make sure things are ok. I do this every 30 or so cycles.
Oh man, I wish there was some kind of flexible configurable BMS being developed at the moment as an open-source project that would allow you to use any battery configuration between 4-12 cells and give more options on what kind of charger to use, while still allowing you to configure what voltage the cells are charged to and also support an e-switch as an optional module for different discharge currents and support multiple comms buses (USART & CAN) allowing you to for example link it to your CAN enabled motor controller and from there forward battery info to your smartphone for live monitoring, so you can run your battery packs the way you want… Oh and also allow for auto-turn off after configurable time (if using e-switch) and allow to discharge the batteries to programmable storage voltage after certain time…
hint, hint, plug, plug…
I’m working on it
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My main issue with running without a BMS is that you get rid of some VERY VERY important safety features. What happens when a cell goes bad? Even quality cells go bad. What happens when your charger takes a dump on you? What happens when your ESC fucks up?
The BMS is meant to be your last line of protection, running without one is careless imo.
Agreed, balance chargers are better in that you get to see a lot more of what goes on, it still doesn’t completely replace a BMS. Remember that a BMS is also a protection circuit. For me, the end game is have protection circuitry on board and balancing circuitry off board. I’m getting close to this with my personal setup but it’s slow going…
@egzplicit, they have several variations of the same BMS. The one I got from Bestech starts at 4.15V and at some point I had one that started at 4.05V. But yeah, the fact that they don’t communicate voltage spread sucks. Which is why I went custom…
