Charge NiMH battery while still in circuit

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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

 

[martin griffith]

On 21 Jun 2006 11:45:36 -0700, in sci.electronics.design

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

 

[Nico Coesel]

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.

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.

 

[Nico Coesel]

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.

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.

 

[Luhan]

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.

Charging NiMH optimally can be very complex. I find it simpler to
simply charge to a 'cutoff voltage'. This gets about 80-90% charge.

http://members.cox.net/berniekm/unichg.html

Good luck,
Luhan

 

[ehsjr]

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

"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

 

[YD]

Charging NiMH optimally can be very complex. I find it simpler to
simply charge to a 'cutoff voltage'. This gets about 80-90% charge.

http://members.cox.net/berniekm/unichg.html

Good luck,
Luhan

Is that fuse really glowing? Looks a bit scary.

- YD.