On Wed, 25 Aug 2010 00:03:09 -0400, Morgans wrote:

"Martin Gregorie" wrote

The only place I've been happy to use untimed chargers is with low
capacity NiCds. My favoured approach there is to use a "1% charge
rate", i.e. charge at 0.01C, and leave the battery permanently on
charge unless I'm flying the model its installed in. NiCds are
frequently used as low- maintenance emergency batteries and these are
invariably left on charge at the 1% rate for years at a time so they
like this treatment. Its really convenient: put the model box back on
its rack after a contest or trimming session, open the lid, connect the
charger and forget about it until next time you go flying.

My strategy for RC NiCads is to charge them with peak charger after
flying, then hook them onto a power strip with all of the other factory
chargers or equivalent which is powered by a 7 day charger. I set it to
come on for 2 hours, once per week.

I found a really simple circuit for building a fixed constant current
circuit plus 'current flowing' LED indicator from an LM358 dual opamp, an
output transistor, a reference Zener and about 4 resistors. I have a
small plastic box containing a row of these, one per model, and simply
run it off a big old 24v mains supply box I built years ago. The circuit
is in the SAMS 'IC OP-AMP Cookbook' but I don't know if thats still in
print.

This works very well indeed for 4 and 5 cell 50 mAh NiCd batteries. They
get fed 900 uA because the dethermaliser timers they drive are always on
(no switch, charging socket in the timer faceplate) and these draw 80-300
uA unless they're releasing the tailplane, when they pull 500mA for 15 mS.

I have one or two higher rate versions sculling round too for other jobs,
such as charging a connection-free 1/2A starter I built, which contains a
set of six NiCd C cells.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |