Designing a constant current power source for NiMH battery charger

[wisepie]

I need to design a constant current power source for my NiMH battery charger. Any ideas are welcomed.

 

[IanP]

Re: Constant current ckt

Very simple constant current source can be build up using the LM317 ..
Here are some details:
http://users.pandora.be/davshomepage/current-source.htm

Regards,
IanP

 

[Meridian]

Re: Constant current ckt

I need to design a constant current power source for my NiMH battery charger. Any ideas are welcomed.

You didn't specify the number of cells. Anyways, the link shown by IanP is excellent!

Keep ohms law in mind (in case of worries ). By constant current charging the *initial* input voltage required to maintain a certain current level can be much larger then the battery voltage.
Meaning, the initial input voltage for a 1.5/500mA NiMH battery (as an example) can go as high as 4volts. So make sure to have enough juice available for the charger to take as much as its needs to keep a constant current charge.

To give you another example. My 12V/8Ah lead-acid battery I use for my radio control is always constant-current charged. 1/10th of 8A is 800mA, but the initial voltage can go as high as 30Vdc depending on the level of discharge.
As the battery charges, the voltage will drop close to 0V when the battery is full.

Close monitoring with this kind of charging is required!