I'm working on a senior project and i am looking for the best way to charge a NiMH battery while it is still in use in the circuit. Basically when the robot senses a low battery condition it hunts out a docking station and docks. From there I'm a bit unsure on how to supply the charge to the battery and when to stop. Any suggestions would be great. Thanks.
Dean
Look at the data sheet for the MAX712/3 charger. Basically the 712/3 has a low value current sense resistor feeding the battery, and it depends on which side of this resistor you take your load from, as to how the system measures the charge current.
FWIW several people have commented that the trickle charge is somewhat high on this IC
martin
NiMh batteries are best charged by sensing their temperature while charging. If the temperature rises more than 1 degree C, they are fully charged. Panasonic had some nice documents on how to charge NiMh cells.
NiMh cells may not be the best choice for your robot. They have a nasty habit of dropping their output voltage very quickly when they are empty.
Oops! Forgot something important. This should read: NiMh batteries are best charged by sensing their temperature while charging. If the temperature rises more than 1 degree C PER MINUTE, they are fully charged.
Charging NiMH optimally can be very complex. I find it simpler to simply charge to a 'cutoff voltage'. This gets about 80-90% charge.
Good luck, Luhan
"Best" is undefined. "Best" can include consideration of what charging power is available, physical size, cost etc. In one scenario, you may need to charge very quickly, in another the robot may not be used for a very long time, so a trickle followed by a taper charge may be best.
For an unspecified "best" use a trickle/taper. The "best" part of that is it won't cook your cells. "First, do no damage."
Ed
Is that fuse really glowing? Looks a bit scary.
- YD.
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