From what I've read, there appears to be a lot of disagreement as to
whether NiCad's are better off being charged with DC or pulsed.

The external chips, such as the MAXIM ones that I've used are constant
current chargers. The charging current depends on the type of cell - some
can be fast charged, some should be charged at 10% of their rated amp-hour
capacity. For example, an AA size standard NiCad should be charged at 45 mA
for about 14 hours. A fast-charge-capable cell might be able to take 500 mA.

The problem with a NiCad is knowing when it is charged. You can't tell the
state of charge by just measuring the voltage. What the MAXIM chips do is
monitor how the voltage is changing. When a NiCad reaches full charge, the
voltage stops increasing and starts to decrease some. That's the point at
which the chip stops charging.

Monitoring cell temperature is also a good idea - when the cell is charged,
the temp starts to rise.

Charging battery packs (batteries in series) rather than individual cells
is harder, as you can only monitor the behaviour of the pack, while an
individual cell may have a different state of charge, and thus be fully
charged before the others. I think this is why most chargers are still
trickle chargers ( 14 hours), as that is a safe rate for all the cells in a
battery.


At 04:51 PM 1/18/2004 +1100, you wrote:
>I would like to use a couple of spare PIC pins to pulse charge a 3.6v NiCad
>battery (aka ). I assume this can be done by using three PIC pins:
>
>* Pin A: detect if external power is applied (ie stop draining the battery
>and start charging it, if necessary)
>* Pin B: send the PWM pulses to the NiCad to charge it
>* Pin C: read the battery voltage to see if it is charged
>
>Pin A & C are obviously straight forward. Pin B is the bit that's new to
>me. I am not sure how simple/elaborate to make the charging circuit. I
>specifically don't want to use an external NiCad charging chips - I don't
>see the point (nor want to go to the expense) since there is already a PIC
>in the circuit capable of doing the work.
>
>I haven't been able to find any circuits or mentions in the PicList
>FAQ/archives or on the web of this being done? Has anyone done it
>sucessfully? Details?
>
>John
>
>
>_______________________________________________________________________
>John Brown                         Email: john.brown@anu.edu.au
>Mobile: 0429 455 504                 Web: www.netspace.net.au/~jabrown/
>
>I don't want to sound paranoid but I think I'm following myself around.
>Everywhere I go, there I am! Sometimes I think it's going to drive me
>around the bend, but at least I know I'll have company when I get there.
>
>--
>http://www.piclist.com hint: The list server can filter out subtopics
>(like ads or off topics) for you. See http://www.piclist.com/#topics

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics