Scooter 1S Spannung nur bis 40,5V, Fragen dazu.

[Patrick14389]

Moin zusammen,
Irgendwo hatte ich mal gelesen das die Scooter nur bis 40,5V aufgeladen werden.
Ist da evtl. Das BMS schuld?

Nicht das die Akkus "schlecht" sind.
Wenn dem so ist dann ist, dann schont das ja deutlich den Akku, da der Akku ja schon ca. 10% weniger aufgeladen wird.
Da ich doch was das Laden angeht, etwas auf meinen Akku achte, finde ich das ganz gut.

Was meint ihr?

 

[AlyMan]

Sie werden bis 41,5 V geladen Ninebot/Xiaomis
Und Yup, das dient dazu um die Batterien zu schonen da ist nicht das "BMS" dran schuld sondern die Ladegeräte schalten bei 41,5 ab

 

[Nobuo]

It happens with all 2020 Xiaomi Mi scooters series (Essential, 1S, Pro2)

Their new BMS firmware comes configured to cutoff charge port when voltage is around 40.8V to then stabilize to 40.4V resting voltage, equal to real 84% of capacity although BMS indicates 100%.

It is slightly more complicated, it doesn't cut the charge by voltage but by reported capacity mAh by BMS.

eg:

Pro2 cut-off charge when BMS report exactly 12160mAh, and then it stabilize to around 11800mAh.

The reason it does not keep at 12160mAh is that the coulomb meter is not precise (or at least it is not the mAh report) so when charging voltage stabilize to resting voltage just when charge cutoff trigger (at around 40.8V with original charger) at 40.4V, so the mAh counter does.

The reason for a large voltage difference between charging voltage just before stop and resting voltage after 5 minutes, is that the charge never enters in CV stage, when charge port cut-off hit at around 40.8V, charger is still in CC stage at 1.7 A, so the voltage rise is huge yet.

When a charger can enter in CV mode, current falls slowly to almost zero, so cells are indeed charged up to the end voltage.

So if you have understood a little how this works, here is a trick to charge a 5% more than possible with the original charger.

Just lower the maximum charge voltage from 42V to around 41.8V. In that case you are forcing a natural CV stage at 41.8V, so when the charge port will cutoff at 40.8V (12160mAh in Pro2), it really will be charged upon that voltage, so then the capacity will stabilize much higher. around 12130mAh in Pro 2 by my testing.

* A very easy 10 cents MOD to the original charger to lower its maximum voltage of around 42V to around 40.8V, is adding in the positive lead a couple of 10A silicone diodes in series. Each one drops the voltage for around 0.6V at low currents (what we need) so both makes a very close end voltage of 40.8V

 

[Speeed]

Nobuo

I don`t have a Xiaomi scooter. Why ist Xiaomi doing this? How are the cells balanced, if the cutoff voltage is 4.04 to 4.08 V per cell? This would only work, if they are using an active balancer. Otherwise there is no way, a single bank would ever hit the 4.2V for "normal" passive balancing/bleeding.

I think, the whole thing is more complex...

 

[Nobuo]

The reason is probably just to improve battery life-cycling, for each 0.1V per series less charge end voltage, the maximum cycle life is doubled. Charging up to around 4.04V per cell should improve life-cycling around a 160% vs charging up to 4.2V

As most simple BMSs work, they only start balancing at around 4.18V, because they usually have each balancing channel independent from the overall series voltage. So they simplify the balancing, doing a top balancing for each series at charge termination voltage ~ 4.2V. Another reason is that it also reduce capacity balancing loss, vs balancing at lower voltages.

A "smarter" BMS indeed could also bleed balance at any voltage per series, as their work principle is usually just activate a FET + bleeding resistor circuit per series. And that's how Xiaomi's scooters BMSs work.

Mi Scooters BMSs are based on BQ76920 IC, they can configure at which voltages or states their bleeding resistors activate (only 5mA though), so they can balance virtually at any voltage level, they probably will do when the BMS report 100% charge (in the case of 2020 scooters, from 80% to 85% real SoC).

 

[Speeed]

Thanks, now I understand how the Mi scooter charging process is working. The bq76930 Datasheet is really interesting.

Not the usual cheap Chinese stuff.