My first post here.
Just got my hands on AliExpress purchased active (capacitive) balancer board. They claim 5A current but it’s probably with max differences between the cells. In 0.1 V disbalance the current will be minimal.
I know there are two camps of BMS and external balancing charger adverts. So asking those who use no bms in their packs.
What if (just as a back up) to use that active balancer as a main charger/balancer with charging circuit applied only to one cell, and the board will be distributing the current to other cells. Surely charging time will be greater (way greater) but if overnight charging who cares.
The whole idea is to use 4.2 cc/cv power supply. Or even any lithium charger that is smaller in cell count that the whole pack. In the last case it even will speed up the process as the bigger chunk of the package is being charged. I’m not a EE so would love to hear reasonable criticism.
https://a.aliexpress.com/_mLGrpaz
That should work in principle
However you are missing a way to switch off charging if one cell for whatever reason gets hot or overcharged, a BMS (internal or external) would do that for you
https://de.aliexpress.com/item/1005004334186734.html
You can very cheap get a DC/DC step up with cv-cc
That can be used to convert a 5 or 12v source into a cc/cv battery charger. Pair that with an external BMS and you have voltage and temperature protection, balancing, all for 10-20 Euro
I use those balancers, it is great in combination of safe charging spot and CC/CV charging. I would still suggest to check the cells before charging them, and not charge to 4.2v per cell until you are sure the pack is balanced to avoid overcharge.
They can move huge amount of imbalance quickly and accurately, but if you need that much your pack is toast anyway
Agree with all the above.
Btw has anyone researched on nature of bms failures?
I had isdt charger with blown one ballast resistor or a bypass transistor so it would not balance that cell but it knew something wrong cuz it is constantly monitors each cell. I wonder what would happen if similar story happened with dumb bms. Would it continue overcharging the cell.
The dumb bms also measures voltages. It can apply balance resistor with transistor, but independent of that, if voltage of a cell gets out of range it will open the in/output. So similar to isdt it will sense balancing is not working and shut off in that case
Dumb and smart BMS is mostly the same hardware, smart just has a Bluetooth module added to read out the values
In comparison this behavior is not the case with a balancer like you shared, as this has no way to switch off the charging current.
Of course no system is 100% fail proof, but not using a BMS is begging for battery fire while charging.
That active balancer has no power input so it cannot charge any cell higher then any cell is already charged.
it just tosses the charge around
Yes, exactly
That’s why it also can’t disable the charger, that’s what I was trying to say
With a BMS you have a shut-off device in line with the power supply in case something is wrong