Servo - September 2007

FIGURE 10

make the pack physically larger and because I need these to fit into a smaller area, I won’t be using them.

First, glue the cells together in the arrangement that you need. I will be making 24 volt packs in the standard 4 x 5 ( 20 cells total) configuration. Here the cells are glued side by side with the polarity of the cells opposite of the adjacent cells.

Once you have all the cells glued together in a flat configuration, let the glue set before proceeding.

Glue four rows of five cells together into a block, again mindful of keeping the polarity of all cells opposite of adjacent cells. I use rubber bands to hold the packs together until the glue sets.

Create a small puddle of solder in the center of each cell. Make sure to let them cool afterwards! (Continuing to solder on the cell while it is hot can damage them.) The solder puddle should be centered and approximately one quarter the diameter of the cell.

I prefer using flexible braid instead of bars for pack construction. It tends to hold up better to hard impacts, and is easier to solder than solid bars. You can find braided grounding cable from many online surplus places for reasonable prices.

FIGURE 11

Here, I have cut the braid into pieces for connectors. About 1.25 inches or so are good for the sub C sized cells — they need to be long enough to go from the center of one cell to the center of the next cell. As with the cells, tin the connecting braid with solder.

Lay the braid across the cells you want to connect, and heat the solder so that the puddle on the cell completely melts into the braid. Be careful not to hold the gun or iron on the cell for too long, as you can damage the cell. This is why a high wattage gun is essential: massive heat transfer lets you perform this step quickly.

The completed solder joint should look like one entirely melted puddle on each end of the braid. Notice in the photographs the pattern of connectors for the bottom of a standard 24V pack.

You can also see the top view of the same pack. Be mindful of the pattern of connectors during construction. You will need to connect all cells in series for the pack. Note the two cells on the left with no connector. This will be where the wire leads are soldered on.

Gauge your wire leads appropriately for the discharge amperage of the packs. I am using 10 gauge

FIGURE 12

FIGURE 13

FIGURE 14

silicone jacketed wire for these.

The shrink wrap that is used on the outside of the pack is easy to puncture, and some protection from abrasion on the connectors is a good idea. You can use thin foam padding (many commercial packs are made this way) or, in my case, I have found that 10 mil pipe tape (found at Home Depot) works well and is inexpensive.