FIGURE 4 FIGURE 6
pack’s final shape and allow to dry.
Bus Bar Installation
Now that we have our pack
shape, we are ready to solder on
the bus bars to form a series path
from one cell to the next (see Figure
4). Solder flux can help here. Care
must be taken to avoid applying
heat for too long or else the cell(s)
may be damaged. The battery will
act as a heatsink drawing heat out
of the iron once the solder starts to
flow, so use an iron with a large tip.
The key is to get the solder flowing
and remove the iron as quickly as
possible. Lay the bus bar across the
terminals and secure it as required
to prevent movement. Again,
routing through tight FIGURE 5
spots. Wire usually
comes jacketed in PVC
or silicone. PVC is
tougher and resists
cuts and abrasions
better while silicone
withstands heat and
better. To install the
leads, strip approx
0.25” of insulation back
and unwind the exposed strands.
Flatten the exposed strands out to
form a V-shape as this will increase
the surface area allowing for a
stronger solder connection.
Pre-tinning the wire is a good idea.
Solder leads using the same method
as the bus bars.
Stranded Wire Basics and
With the bus bars installed,
solder the (+) and (-) leads. Consult
an American Wire Gauge (AWG)
table for the correct size wire based
on your system current. Choose
black for negative (-) and red for
positive (+) connections. (Note that
these images show white for
positive which is not recommended.
At the time of assembly, we ran out
of red so the white was later made
red with a large sharpie!)
Wire types vary but generally
speaking the more strands, the
more flexible the wire. Deans Wet
Noodle™ and Astroflight™ wire are
favorites among robot builders.
Flexible wire can be important if
Shrink Wrapping the Pack
Once the leads are attached,
the pack is ready to be shrink-wrapped. Before this is
accomplished, secondary insulation
such as thin sheets of
Teflon (see Figure 5)
or high temperature
fiberglass tape may
be added for extra
insulation, if desired.
Shrink wrap has a
neat ability in that it
shrinks radially but not
axially. Cut a piece of
heat shrink just long
enough that it can be
folded to cover the
ends of the pack. Cut
two holes for the leads
to pass through. Slide the pack
inside and leads through the holes.
Using the heat gun, carefully begin
passing the heat over the wrap.
Don’t allow the heat to remain in
one area too long or you may melt a
hole in the wrap (Figure 6). Once the
wrap is finished shrinking, you can
reheat the ends to soften them and
carefully fold them over the ends of
the pack with a small block of wood
or a plastic spatula. Crimp on your
desired connectors and your pack is
fit for combat! SV
SERVO 10.2008 29