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.
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
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
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.
Cut the shrink wrap so that it
overhangs the pack about 1/2 inch
SERVO 09.2007 29