Servo - October 2008

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, solder quickly!

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 harsh environments 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

Lead Attachment

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