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12 hours ago, esaj said:

Yes, I understood the problem there, but is this common to all wheels, or just for IPS?

My knowledge about batteries of other EUCs(apart from IPS and Gotway) is quite limited therefore I cannot give an definite answer to this question. What I can say is that I experience many cases of severe unbalancing of IPS EUCs including 3 times on my own T260(which is my first EUC). However, severe unbalancing never happened to my three Gotway EUCs probably they use quality cells, or I've paid more attention to the charging, or they use smaller balancing resistors(120 Ohms).


12 hours ago, esaj said:

The balancing procedure can proceed as follow:

  1. Initially, the balancer is turned off after the battery charger is connected.
  2. When any battery cell reaches 3.65V, the BMS will turn on the balancing circuit in this channel, and the discharge resistor in this channel will slightly drain the cell.
  3. When any cell reaches 3.9V, the BMS will turn off the charge current by the power transistor in the charge line.
  4. At that time, all the cells whose voltages are higher than 3.65V will be still being drained by the discharge resistors in their channels. This way, all the high cells will be discharged to 3.65V.
  5. When the highest cell drops to around 3.7V, the BMS will connect the charger again.
  6. Note that, at this time, there are cells that are still below 3.65V.
  7. Return to 2.

This turn-on and turn-off repeat cycle may or may not happen, depending on the type of BMS used. That may well be the case for Gotway EUCs where they use descret componets(but I didn't test it, the problem-free of my gotway batteries seems to support this). However for IPS EUCs, once the cut out happened, it may not turn on again because they use smart ICs(MAX14921) for BMS, and the unbalanced situation cannot be recovered by prolonged charge.

Chart below is one of the case(cell voltage distribution) for a T260 where cell 16 is over charged and triggered the charge protection while cell 14 is way out.

Even for simple BMS such as link below, the overcharge release voltage is 4.15V, lower than the balancing release voltage(4.18V), that means the overcharge may not be released as a result of bleeding current, thus the turn-on will reluctant to occurs, at least we have to wait for a very long time so that the voltage drop from 4.18V to 4.15V because of very small leakage current.

Furthermore, the voltage difference for Li-ion battery from the balancing start(4.18V or 4.20V) to over-charge protection voltage(4.25V) is small(0.05V to 0.07V), the time for low voltage cells to catch up is limited for each turn-off and turn-on cycle, if the cycle does exist. While in the case of LiFePo4 batteries, the difference is many times larger(3.9V-3.65V=0.25V).

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