
STARLET Battery Recharging                     Date: 06-05-1987 20:18:58
By LOU GENCO

The NEC Starlet has a tendency to drain its C-cells rapidly, even when
turned OFF.  Several suggestions were given here to help reduce power
drain.  These suggestions require disconnecting one of the C-cells (with
the little red ribbon in the battery compartment), turning OFF the
backup battery, or some combination of the above.  The problem is more
apparent with NiCads than with other battery types because of their
lower amp-hr capacity.

I thought there might be a way to construct an internal recharging
circuit for the NiCads, but they require around 6 VDC, and the Starlet
AC adapter supplies 9 VDC.  Also, loading the AC adapter with both a
recharging task and the normal "working" load might cause eventual
failure.  Finally, I didn't want to mess up the nice wiring job NEC did
inside the Starlet.

I eventually constructed an inexpensive portable external recharger that
recharges my GE NiCads at 110 ma, 1.25 v/cell.  If you want to try it,
you will need the following parts (available at Radio Shack): Two double
C-cell battery holders; One 1N914 (or equivalent) diode; One coaxial
connector (a jack to fit the power supply plug); A 1/2 watt resistor
(about 300 ohms); A LED (optional)

Glue the C-cell holders back-to-back.  Trim the power leads, and solder
a red wire from one holder to a black wire (wire the two holders in
series).  Connect the remaining black (-) and red (+) wires as in the
following schematic:


    + |------------------|<--------|<-------/\/\/\/------------->
      |                  D1        LED (and/or) R1    To sleeve
     _|_
      _
     ___
      _
     ___  Battery holder
      _
     ___
      _                                               To post
  -   |---------------------------------------------------------->
=

The current limiting resistor (R1) should be chosen to allow 80-100 ma
charging current to the GE NiCads.  Empirical determination with a
milliameter or VOM is fine.  I replaced the resistor with a LED that
dropped the current sufficiently, and allowed a positive visual signal
when the batteries were charging.  (I had the LED in my junk box, and
don't know the specs).

I then encased the wires, diode and connector in potting compound
(leaving the LED peeking out), and affixed the whole thing to the top of
the C-cell holder.  The unit is very light and small, fits in my travel
case, and appears to work well.  Unfortunately, one must remove the
C-cells from the Starlet to recharge them; and simultaneous battery
recharging and Starlet usage is not possible.

So far, the set-up has worked, and hasn't blown either my batteries or
my AC converter; however, the usual disclaimers apply...  I am not
responsible for damages to your equipment if you try this thing.

I think the same circuit could be put on a piece of perfboard and
connected internally to the Starlet's power-in jack, so there might be a
more portable option ...  but I didn't want to overload the power
supply.  I'd appreciate any notes from adventuresome folks who try the
internal version.  Trickle-charging the NiCads while working on the
Starlet would be a nice feature!

Lou Genco
