Rechargeable battery question

I have a NiCd 9.6V 1600mah battery pack, when i designed trickle charger(160 ma -- 0.1C charge rate) for it i used the 9.6V value... The problem is that the voltage of batt during the chrging raises to 11 V immidiately and after couple of hours it raises to 11.5 V... In turn the current going into it is about half of what it should be. When removed from the charger the voltage of battery pack is 11V. My question is... What is the voltage of the rechargeable battery represent? it clearly isn't the voltage of the battery pack, also how can i predict the actual voltage of the rech. battery during charging.... I dont care about other chemistries
i am dealing with nickel based batts for now.

If you want to keep a nickel cadmium battery topped up without damaging the battery use currents of between 0.05 C and 0.1 C ..
And don't worry about the voltage .. it is dependent on temperature, so be sure to regulate the current in the charger ..

Regards,
IanP

Hello
The nominal voltage of a NiCd cell is 1.2V. So I think that you used 8 cells in series to make a battery pack of 9.6V.
The voltage of any healthy cell may range from 1.1V to 1.65V. So, the overall voltage of battery pack may range from 8.8V (minimum voltage during discharging) to 13.2V (maximum voltage during charging).
You Have to stop the charging if the pack reached the maximum voltage. as exceeding this voltage is very harmful for the cells and it may cause chemical problems.
as you might know each cell has an internal resistance. So the Apparant voltage V can be calculated from the equation :
V=E+I*R
where E is the internal voltage and R is the internal resistance. when I=0 , V=E
you dont have to care about the value of E during charging , as long as your batteries are healthy.
To keep you cells healthy , dont ever over charge them or deeply discharge them ! you have to charge/discharge the whole pack together to keep the cell as identical as possible. DONT work on any cell individually as the mismatching between cells will lead to balancing problems.
I wish this info is benefiting for you. fell free to ask any question
Ahmed Salah

Thanks a lot Ian and ahmed.

In my charger the current going into the battery is too low if the voltage of the pack is higher than assumed during the design process. All i have to do is redesign it using the 14V as the voltage of the rechargeable battery. Another question that i have What if you have a solid battery ( not individual cells 1.2v batteries in series ) say 12V (still talking about nickel based chemistry). Would it be reasonable to divide it by 1.2 and than multiply it by 1.65, and use this value as the maximum voltage of battery? Do they make solid batteries like that?

Good idea about the charger , but you you have to monitor that the voltage of the pack doesnt exceed 13.2V during charging. By the way, what is the model of you batteries ? which manufacturer?
NiCD battery packs are made up of several cells connected in series , basing on 1.2V. So 12V battery pack is made of 10 cells. you can use the same concept in charging the pack as charging 10 cells connected in series.
There is a very good site about NiCd batteries:
https://en.wikipedia.org/wiki/Nickel-cadmium_battery
you can also have a look at Nickel Cadmium Technical Hand Book


It is also very useful to download the datasheet of your own battery pack and look at its charging curves

Regards

Yeah i am using the battery pack i bought in radio shack. 9.6V NiCd 1600mah.
they didn't provide any data sheets. Thanx a lot ahmed.

nominal voltage of rechargeable batteries 1.2V but they can reach 1.45V at full charged so a battery with 8 cells can be 13.8V from 9.6V.
you may try different charging methods, for Ni-Cds best one is constant voltage and constant current charging. you can use a timer or following voltage (and shutting automation) or following temparature (for fast charging).