Gayan Soyza
Active Member
I’m planning to design a charger for NI-MH rechargeable batteries due to unavailability of NI-CD batteries. I know it’s not easy to build a charger for NI-MH Bcuz it must be treated well than other types. Some how I must take the risk of this project.
Batteries I’m going to use/charge – (AA) NI-MH 1.2V, 2550mAh, standard charge 16Hrs at 260 mA. I’m going to charge two batteries in series.
As far as I know about rechargeable Nickel based batteries NI-CD & NI-MH are treated almost using the same principles like feeding constant current & voltage……but taken into mind the charge rate for NI-CD is 0.1C & for the NI-MH trickle charge rate is below NI-CD 0.05C-0.1C. Also considering when to stop the charge.
Before building the circuit I decided two methods for NI-MH charges. Listed below.
Method1
Using LM317T as a current source in series with a current limiting resistor applying to the batteries & turn off the supply power within a calculated time.
According to my battery spec, it will be 255 mA charging for 14Hrs & turn off the supply power.
But for half charged battery will it be a problem? They will charge quickly or overcharge?
What will be the result if I change the C rate about 0.090C.I heard that NI-MH must rapid charge rather than slow charge.
Method2
Using a comparator IC to detect the battery voltage if it is come to a certain level the output driver will cut off the supply or adding a PIC chip to this stage deciding whether to do a very small trickle charge or an occasional pulse charge or a Timer cutoff condition.
These are the two methods I can do at home .for detecting temperature, pressure, voltage drop per cell in mV would be consider later. And also I cannot find any battery charge controller IC’s in my place.
So I need some pickup from you guys. Any comments on these methods, what’s the best way? What are the missing points?
Hoping a reply soon.
Thanks
Batteries I’m going to use/charge – (AA) NI-MH 1.2V, 2550mAh, standard charge 16Hrs at 260 mA. I’m going to charge two batteries in series.
As far as I know about rechargeable Nickel based batteries NI-CD & NI-MH are treated almost using the same principles like feeding constant current & voltage……but taken into mind the charge rate for NI-CD is 0.1C & for the NI-MH trickle charge rate is below NI-CD 0.05C-0.1C. Also considering when to stop the charge.
Before building the circuit I decided two methods for NI-MH charges. Listed below.
Method1
Using LM317T as a current source in series with a current limiting resistor applying to the batteries & turn off the supply power within a calculated time.
According to my battery spec, it will be 255 mA charging for 14Hrs & turn off the supply power.
But for half charged battery will it be a problem? They will charge quickly or overcharge?
What will be the result if I change the C rate about 0.090C.I heard that NI-MH must rapid charge rather than slow charge.
Method2
Using a comparator IC to detect the battery voltage if it is come to a certain level the output driver will cut off the supply or adding a PIC chip to this stage deciding whether to do a very small trickle charge or an occasional pulse charge or a Timer cutoff condition.
These are the two methods I can do at home .for detecting temperature, pressure, voltage drop per cell in mV would be consider later. And also I cannot find any battery charge controller IC’s in my place.
So I need some pickup from you guys. Any comments on these methods, what’s the best way? What are the missing points?
Hoping a reply soon.
Thanks