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This post provides a wealth of information about battery balancing an Onyx RCR and CTY2, including any PEV (eBike, eBoard, eScooter, and EUC). With this information, battery balancing can be verified, since not all Battery Management Systems (BMS) provide auto battery balancing with or without a balance-compatible charger.
In any personal electric vehicle, you have a battery pack consisting of multiple individual batteries on average ranging from 160 (72v) individual batteries to 200 (72v) individual batteries. These individual batteries are almost always Lithium-ion 18650 or 21700 NMC (Lithium Nickel Manganese Cobalt Oxide) type batteries. Each one of these batteries will operate fully charged at 4.2 volts and discharge to 3.0 volts.
It is normal and expected for individual battery cells in a battery pack to slightly drift apart in voltage from each other, which is refered to as "cell drifting" as in an unbalanced state. There is no preventative measure for cell drifting, which is taken care of by the BMS. Cell drifting happens because of loads placed on the battery by time, peaks, constants, temperatures, and regenerative braking. When many or a few individual battery cells are at a slightly different voltages, that is commonly meassured to as "cell delta". Cell delta reading are generally values from a helathy 0.005 volts to 0.040 volts, as in the lower the cell delta value, the better.
The battery management system (BMS) located inside the wrapped battery pack manages battery balancing. In the balancing function, it balances the charge voltage of the battery cells to be as close as possible to each other in voltage with a value of 0.005 volts being excellent.
Not all battery management systems (BMS) operate the same when it comes to battery balancing. Some will require that a balance-compatible charger be plugged in for a duration of time to activate the battery management system "balance function". Other battery management systems (BMS) do not require a balance-compatioble charger or any charger to be plugged in for the "balance function" to operate, instead they continuously balance the battery automatically.
Newer battery management systems are capable of displaying their real-time reading through an iOS or Android app via Bluetooth, independant of the bike. These newer battery management systems also display battery series voltage levels and the battery delta voltage value.
In passive battery balancing, energy is drawn from the most charged cell and dissipated as heat, usually through resistors. In active battery balancing, energy is drawn from the most charged cell and transferred to the least charged cells, usually through capacitor-based, inductor-based, or DC-DC converters.
Not all battery management systems (BMS) are capable of balancing the battery and can only manage the charge current limit, discharge current limit, and internal impedance. An inexpensive, non-destructive, and easy way to verify if a battery management system (BMS) is capable of balancing a battery is with an outlet meter and time.
Not all battery management systems (BMS) are capable of balancing the battery and can only manage the charge current limit, discharge current limit, and internal impedance. An inexpensive, non-destructive, and easy way to verify if a battery management system (BMS) is capable of balancing a battery is with an outlet meter and time.
Test a battery management system (BMS) that is charger dependant (balance compatible charger) for the "balance function", by plugging the charger into the “outlet meter” and having the meter set to display watts. Check the meter 3 hours after the battery has been fully charged to 100%. It should display 2.9 watts and above with every few seconds fluctuating higher to 3.2 watts or above. If it does, then that means the battery management system (BMS) is capable of balancing the battery. If the outlet meter reads 0.5 watts after three hours from the battery being fully charged, then that means the battery management system (BMS) is incapable of balancing the battery.
All batteries take extra time to charge from 97% to 100%. This is called “constant voltage charging (trickle charging)” and is not the same as battery balancing. A 72-volt battery in a 20 series and 8 parallel arraignments with a charger ranging from 2 to 8 amps will take roughly 95 minutes to charge from 97% to 100%.
Most battery management systems (BMS) are the kind that requires the charger to be plugged into power on the battery management systems itself so it can balance the battery. The other kind of battery management systems that can power themselves from the battery is more expensive, which is why they are not common.
Different battery voltages and how long it takes to balance them.
Using the outlet meter readings, it can be determined at what state the battery is at regardless of it being 100 volts, 72 volts, 52 volts or 48 volts because they all share one common thing, and that’s either a 18650 or 21700 battery.
Regardless of how many amps a charger is capable of outputting ranging from 2 amps to 12 amps, it has to follow the same rules of trickle charging, constant voltage charging, and battery balancing.
If the battery management system (BMS) is capable of balancing the battery, then the gains are performance, longevity, and the absence of numerous voltage-related issues like premature cutoffs. A battery management system (BMS) that can’t balance the battery will result in a PEV whose range and performance will diminish more quickly.