Idea on charging voltage and current of 15 1.2 NiMh 3000mAh batteries

[hafrse]

Hello,

I purchased a battery charger PCB https://www.aliexpress.com/item/1005001770435239.html?spm=a2g0s.9042311.0.0.dcd44c4dDx8wCa that supports battery packs 6-24V with adjustable charging current. I have 15 1.2v 3000mAh (china) AA batteries, total 18V. What is the recoimmended max and min charging current and voltage ?
Thanks

George

 

[KlausST]

Hi,

apparently you did not do an internet search on your own.

I guess this, because every single document that talks about charging batteries should mention that this mainly depends on battery chemistry.

I recommend to read through batteryuniversity.com for some good, reliable informations.

But chemistry is not the only thing. Even if you have batteries of of same chemistry and same size (like "AA") it does not mean that they all have identical charging parameters.
Let´s say "AA" type NiMH. Different types, different brands. One may be designed for long life, the other for low or high temperature, the other for high current pulses .... all result in different optimal charging current and charging modes.

And "charging current" is not the only thing.
There are different charging modes and how to detect that a battery is full. Some do this by monitoring the voltage, others do this by monitoring battery temperature, some both.

And then there is the charging time.
a battery may be used in an emergency light. Continously connected to the charging unit, much time to charge the battery. Thus you may use a rather low charging current.
On the other hand you may have a battery powered drilling machine. You want to use it as long as possible and you want to charge it as fast as possible. --> rather high charging current.

And then there is the problem with charging batteries connected in series. So all see the same charging current. But one cell surely is weaker than the other, maybe older, maybe has a different charging level. So ideally all need different charging time. Some battery chemistry can stand " a bit of overcharging" some others react in reduced lifetime, some others tend to explode.
Thus some batteries need a so called charge balancer.

Conclusion:
It charging current depends on
* chemistry
* brand and type
* charigng time
* charging mode
* expected lifetime
* temperature

The best way is to use: all identical batteries, same age from a reliable manufacturer, who provides a good datasheet with charging informations.

If you don´t get charging informations, you need to go your own safe way. Low charging current, rather low "charging end voltage". Safety first: you have to avoid overheating and explosion.

Klaus

--- Updated Dec 11, 2021 ---

Added:

Sorry, now I see you mentioned "NiMH" chemistry in the headline. I just searched the text for this information.

Klaus

 

[hafrse]

Thanks for the informationm, this is what the charger board manufacturer says.

• Fully charged without self-stop function Please control the time according to battery capacity and charging current. (For example: 1000mA battery selects 200mA current charging time is about 6 hours full charge)
• The power supply of the charging board should be greater than the charging battery voltage of 5V or more.
• Delctable charging current 50mA, 100mA, 200mA, 300mA

The power supply to the charging board is 24V , I measured the charging viltage at 24 supply and it was also about 24V, so that is 6V above 18V of the 15 cells in serial.
May be I should use 50mA @24V charging voltage to be safe and stop charging depending on the capacity of the batteries and the charging current
The board is using LM2596S device.
George