Do any BMS's balance at 4.1V instead of 4.2V?

I've got a laptop pack that I repurposed that came with lithuim prismatics 3s 3700mah, They have been around the block a few times now around 5 years old I used them in my scooters as an aux batt for lights etc and powered my 5 metres led push bike for blackpool ride the lights.

When i used the pack last august all was healthy each cell had around 40 milliohm, held a full charge and all cells charged at the same rate and balanced nice and evenly and fairly quick to. The pack was left at 3.4v fairly balanced and in a cool climate for the last 9 months, Now I tryed to charge it and only the centre cell is ok both outer cells Ir has doubled and their charging rate is all over the place they had peaked at 4.2v when the centre cell was still sitting at 3.84v so a none intelligent charger would have pushed that sucker clean into overdrive needless to say im using just the one cell left now in a bluetooth speaker the rest are history.
 
They served a good life had some ups and downs proberly over 500 of them, Its strange because I've heard of dentrites forming during charge and discharge but I've had a few batts fall on their arse while being stored in decent conditions, my ps4 controller less than a year old holds 20 mins charge.
 
fechter said:
The quality of the cells makes a big difference.
Click to expand...

exactly, and also how the pack has been made (connection of the groups).
equal curent flow through all cells is very important, and it also means equal cell temperature.
 
madin88 said:
fechter said:
The quality of the cells makes a big difference.
Click to expand...

exactly, and also how the pack has been made (connection of the groups).
equal curent flow through all cells is very important, and it also means equal cell temperature.
Click to expand...


Could you elaborate on that? You mean already in the design of a battery make sure each cell has equal length bus bar? Is that at single cell level, or the P group or S group?
 
Anything that makes current flow unevenly with in the pack is going to age the cells in a differential way.

Be it manufacturing tolerances or non pack symmetry making cells work harder than others.
 
Crap, I am doing a scooter conversion and landed on an odd shaped "L" for the battery for max capacity. But I guess it is to be done over again to get more optimal current flow. Hm guess it is back to cardboard boxes, carpet knife and scotch tape to try to find a better way to have all connections equal.
 
JoeFR said:
I bought this Smart 24S BMS. It has PC management ( USB ) and bluetooth management via android app.

I hope it work OK I have to test it in my E-bike pack.
Click to expand...

Please let us know how that works out. Sometimes deciphering the instructions is the hardest part.
 
See how low the high volt protect will go. Try 2.75 volts hvc.
I have a couple of these in 14s. Have not had time to test, if someone wanted to try one.
 
It would be helpful, in addition to the corrections and suggestions if posters listed any available BMS. I mean any available to the DIY builder. Here's one from another thread. https://www.energusps.com/shop/product/tiny-bms-s516-30a-16?category=4

Does anyone know how to parse specifications to determine HOW a particular BMS does balance the pack?

Also, using the Satiator is there a best practice for charging a pack at 80-90% ? Regardless of the BMS?

T
 
tomjasz said:
It would be helpful, in addition to the corrections and suggestions if posters listed any available BMS. I mean any available to the DIY builder. Here's one from another thread. https://www.energusps.com/shop/product/tiny-bms-s516-30a-16?category=4

Does anyone know how to parse specifications to determine HOW a particular BMS does balance the pack?

Also, using the Satiator is there a best practice for charging a pack at 80-90% ? Regardless of the BMS?

T
Click to expand...

From the link that BMS uses resistance to balance the cells "Cell balancing: 150 mA, dissipative"

Using the Satiator, you can simply set the cutoff in the software to whatever level you please. I have mine set to 85%. The Satiator uses the whole pack voltage to determine the cutoff voltage, so it's really independent of any BMS you have installed.

-Jim
 
As was implied (I believe) in one of SMs articles, there really isn't much incentive for battery manufacturers to advertise the fact that NOT fully charging a given cell could significantly increase its lifetime. IF, however, a car company offers an 8 year warranty on their vehicle's battery pack, you can bet they're going to make damn sure that battery isn't going to crap the sleeping bag BEFORE that warranty runs out.

Basically what I'm getting at is that manufacturers aren't supplying the market with cheap BMSs that balance at 4.1 volts simply because not enough people are asking for them. We see a cell can be charged safely to 4.2V and think "good then, that's what I want to charge it to," and so that's exactly what we end up getting and if that means buying a whole new battery sooner rather than later then so be it. It's not hurting Samsung/Panasonic/etc. at all..

Some time ago a certain member was advertising an adjustable balance board (PCB only) in the for sale section that used little trim pots to set the balance charge of a given parallel group of cells. It was quite brilliant, I thought, though for whatever reason he seemed to have no interest in marketing them as a finished product. A pity for those of us with poor soldering skills. I guess we'll just have to find other ways to get by.
 
I've got a crappy Chinese 35a bms that'll cutoff the charge at around 4.18v per cell. Ends up just under 54v total. I think it's an issue with my charger not dropping down the current as it gets closer and closer to the full cell voltage but it works. Kinda annoying I can't top off the voltage but it's plenty of range for me and I guess it'll help save the life of the cells....
 
i believe this is programmable https://www.aliexpress.com/item/20S-50A-2017-new-Li-ion-smart-bms-pcm-with-android-Bluetooth-app-UART-correspondence-bms/32809939362.html
 
http://chargery.com/ bms-24 300amp standard.

Expensive but very informative remote display.

I use them in gem cars and golf carts.

You can also set the balance function in the cheap bt bms.

But its so nice to watch amps, volts, and kwh. While driving.
 
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