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Die nominelle Akku-Kapazität ist eine sehr theoretische Angabe.
Seriöse Hersteller geben die Lade- und Entladeschlussspannung an, und den Entladestrom.
Meist wird mit einem Entladestrom gemessen, der praxisfremd ist, und von 4,2 bis 2,8 Volt entladen.
zB LG INR-MJ1 ist spezifiziert mit 3.350mAh, gemessen mit 3A Strom sind es 2.960mAh und bei 5A Strom nur mehr 2.790mAh.
2.4A for standard m365 and S1, Pro and Pro2 BMS firmware accepts more than 4A, I have not tested yet the very maximum
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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
Thank you very much for your explanation. So what we really need is a modified BMS Firmware to rise the charge cutoff trigger. I guess Xiaomi just lowered the cutoff trigger so that you can drive downhill with a fully charged battery and use the electronic brake without burning the controller (a problem with the M365 Pro).
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
[QUOTE = "Janophibu, post: 7578, member: 1968"]
Thank you very much for your explanation. So what we really need is a modified BMS firmware to rise the charge cutoff trigger. I guess Xiaomi just lowered the cutoff trigger so that you can drive downhill with a fully charged battery and use the electronic brake without burning the controller (a problem with the M365 Pro).
By the way you meant 40.8V?
[/ QUOTE]
Exactly, BMS firmware control when the charge cutoff trigger.
Yes * 40.8V * sorry I made a typo!
That is a very plausible reason, indeed it is just about voltage. As lower is the battery voltage, the lower is the voltage spike by KERS or regenerative brake. But I am not 100% sure the reason.
In any case there are advantages to the average user that use to charge always to 100% and leave it for days, they will increase battery life dramatically as there is a much lower high voltage storage degradation.
[QUOTE = "michi_gecko, post: 4950, member: 66"]
The nominal battery capacity is a very theoretical figure.
Reputable manufacturers indicate the final charge and discharge voltage and the discharge current.
Most measurements are made with a discharge current that is not practical, and discharges from 4.2 to 2.8 volts.
Eg LG INR-MJ1 is specified with 3,350mAh, measured with 3A current it is 2.960mAh and with 5A current only 2.790mAh.
[/ QUOTE]
I shall add my grain of sand for this. It it very correct that when cells are tested and measured at different current levels, capacity reports from the tester are different (higher current, lower mAh), but it is not the real capacity "available" at such continuous current levels on the cell measurement . Believe it or not, the cell discharge capacity is not dependent on discharge amperage or temperature, but voltage is, so energy and power also are. This means that no matter at which current you discharge a cell, if you discharge it upon the same resting voltage, eg: 3V, you will have discharged exactly the same capacity. What it will be different is how the voltage behaved during discharge upon you finish with the cell at the same resting voltage.
As higher is current, higher is voltage drop, and that means that minimum voltage will be reached sooner for a higher capacity remain. So as higher is the current discharge, also it is higher the resting voltage when the charge stops, indicating the real capacity it remains in the cell is also higher. This is not very wrong, because chargers / testers measure available capacity inside 'operative voltage window', it means that when the voltage is too low, it stops the test because that remain energy was not usable because the voltage was too low. If you restart the testing upon having the cell at the same resting voltage, eg: 3V, the capacity measurement will be the same. Just for curiosity, this not happen in all battery technologies, for example in lead acid batteries, as higher is the current, the discharge capacity in INDEED lower.
The 'nominal' or 'rated' capacity is a rounded value that has its minimum specified in 'minimum capacity'. This value is not only not theoretical but very absolute.
My charger is only at 41,7V stock without load. So I added only one Diode and then had 41,4V without load. I charged my scooter and got only 11.624mah instead of 11.800mah stock. So for me this method does not work, lower the charger voltage seems to lower the charged capacity.
My charger is only at 41.7V stock without load. So I added only one diode and then had 41.4V without load. I charged my scooter and got only 11.624mah instead of 11.800mah stock. So for me this method does not work, lower the charger voltage seems to lower the charged capacity.
Diodes voltage drop are dependent on the type of diode and current. For example a 10A10 silicon diode has a voltage drop of around 1V at 2A, but only 0.6V at 100mA. A Schottky Diode can be as low as 0.2V.
Measure voltage with disconnected charger from scooter.
Try to get 40.8V
Very important, report how the difference in resting voltage is, instead of mAh, voltage is an infallible method to calculate SoC (system of charge). Do it after stabilization, around 10 minutes after charge stops (12160mAh)
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