• Put everything on one face of the board before you
try to solder the parts. Just get them on top of the
pads and oriented close to correctly; you can fine-tune as you solder. The wet flux will hold things in
place until you are ready to start soldering.
• I hold the tweezers in my left hand in such a way
that the little finger of my hand is resting on the
work surface. I then move the components around
by moving my arm, not my fingers. (This is how
artists who work on master dies for coins do it.)
• The method for SMT soldering I’ve found
recommended on several websites — “Put some
solder on the pad, hold the component in place, then
melt the solder” — works okay, but I prefer the
following. I just put a tiny dab of solder on the end
of my iron, hold the component in place with the
tweezers, and touch the iron to the joint between
the component and the pad. Surface tension does
the rest. Use a very fine lead free solder; .020” size
works for me.
• Don’t worry about having a little extra solder on the
component, and don’t worry about the part being
perfectly lined up. Hold the iron on the part for
about a half second, then pull it off and give it a
second to cool before letting go with the tweezers.
Solder one pad on all components, then go back and
finish that side of the board.
Check your work under high
magnification (at least 10X),
flip the board over, and
repeat.
• You will need to pull the
battery connectors off the
old board that comes with
your sacrificial charger. I’ve
found that the best way to
do this is to simply load up
some solder wick with flux
and get all the solder to wick-out. Then, gently bend up
the tabs that hold the clip in
place and then heat the leg
again while gently pulling on
the part.
• You will need a new power
supply to run your fast
charger; the one that comes
with the Versapak chargers
doesn’t put out enough
voltage (or current). Anything
that puts out approximately
12V at 1A should work. I
found a deal on some scratch
and dent linear supplies, but
a switching supply would
work okay as well. Most of
the 12V wall wart supplies I
have tested put out more than 12V,
but you should be okay with a few
extra volts. I wouldn’t go much
higher than around 16V.
• Once everything has been
assembled and you place the new
and improved board into the
Versapak charger/holder (Figure 4),
you can plug in the power supply.
The LEDs should flicker briefly then go out. This is an
unintentional feature, but it lets you know you have
hooked up the power and everything is working. So,
I didn’t try to fix it. When you plug a battery in, you
will get an orange light (red for fast charge plus
green for trickle charge equals orange) showing that
the charger is working and attempting to charge the
batteries. When the batteries are almost fully
charged, you will see the light switch from orange to
green and then back to orange periodically. This is
the smart charger chip shutting off the fast charge
circuit in order to get an accurate reading on the
battery voltage. Given enough time, the LEDs will
stay green, indicating that the batteries have been
charged and the charger has changed to trickle
charge only mode.
Enjoy! SV
SERVO 09.2010 51