A novel and practical method for equalizing charging of nickel-hydrogen battery packs

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A novel and practical method for equalizing charging of nickel-hydrogen battery packs [Copy link]

It is extremely complicated and even impossible to balance the current of hydrogen-nickel battery packs by voltage detection, and its reliability is also extremely complicated.

However, hydrogen-nickel batteries have a feature that other batteries do not have. When fully charged or nearly fully charged, if a current lower than 0.1C is used for charging, the batteries that are not fully charged will continue to charge, and the fully charged batteries will become heat and dissipate. In this way, the capacity of the batteries that are not fully charged increases, and the heat generated by the fully charged batteries consumes the charged power. This method can achieve the balance of the series battery pack.
This method also has some prerequisites.

For example, after the battery has undergone multiple cycle life tests, the capacity will decrease. In this way, 0.1C should no longer be selected according to the nominal value. For example, if the battery capacity margin is selected according to 0.7 times the nominal value, should it be selected according to 0.07C of the nominal value?

There are requirements for heat balance and heat dissipation design.

The charging time below 0.1C should be within the allowable range.

I published this method after successfully testing the small current charging and balance recovery test in the hydrogen-nickel battery charger of electric bicycles. Netizens can also verify and communicate as much as possible about the problems found, and improve together!
In the test of nickel-hydrogen batteries, there is an overcharge test, which is: 0.1C charging for 48h, no leakage and discharge to reach the standard capacity. During our test, the battery basically has no heat, that is, the temperature of the battery rises very slowly, generally up to 33℃.
Of course, the electric vehicle battery is closed, the heat is not well dissipated, and it is easy to accumulate. It is recommended to use a current of 0.03C~0.05C to replenish the power, but the time is slightly longer. However, for the long-term use of the battery, there is basically no harm, the heat dissipation is slightly better, and the battery pack basically does not heat up! Now professional nickel-hydrogen electric vehicle chargers have this function.
The following data is still my experience when I was doing research and development. I haven't done it for a long time, so it may not be accurate!
Take the large-capacity nickel-hydrogen battery of electric vehicles as an example:
using 0.3C charging, the surface temperature of the single cell is: about 38℃, and exceeding 42℃ means that there is a problem with the battery! In a closed environment, the temperature of the combined battery generally rises to 43℃. If it exceeds 48℃, the battery pack will be overcharged. Such a current is relatively large. If the current is smaller, the corresponding temperature will be lower.

When using 0Δ charging or dT controlled charging, the battery has been slightly overcharged. Generally, the battery has a voltage drop when it is charged to 1.03~1.06 times the standard capacity. Strictly speaking, the battery is not fully charged at this time, and it has reached about 92.5% of the power. Using 0.05C to supplement the power, 2~3H is enough!
As an electric bicycle hydrogen nickel battery charger, it should be considered that the longest charging time is no more than 8 hours.
Another consideration is to prevent the growth of crystal dendrites. The current of large current charging should not be lower than 0.4C. In this way, the early high current charging is sufficient for 2~3 hours, and the later supplementary small current charging time is considered to be no more than 5 hours. If the nominal capacity of 0.07C is used, the power that can be charged in 5 hours is 0.35C. If the positive tolerance of the battery capacity is taken into account, it is also possible to consider increasing the time for timing termination charging. Among them, according to the small current (0.07C) for 5 hours.