Having acquired some copper bar from a scrap yard, I set out to make bus bars. While I could have purchased pre-build bus bars within a prebuilt metal electrical enclosure the cost at this time wass too expensive. In stead of hundreds of dollars only twenty dollars were spent. The original copper bar was 1″ x 1/4″ x 48″ and was cut down to four 12″ pieces. I then drilled 8 holes sized for attaching the battery cables, one hole for 4/0 lugs of the main line, and 2 more holes for attaching the bars to the wall. The four bars were doubled up one on top of the other to make each positive and a negative bus bar.
I then used some of the scrap galvanized steel (1/8″ x 1″ x 3′) laying around the garage to make holders for the bars. Using a bench vise I bent each of four holders and then cut them from the stock piece. All together I made five of them: two for each bar, and one for the main cut-off switch.
Why use bus bars?
The decision was made to use bus bars because it made it very easy for additional batteries to be added. It also meant that if one battery failed the other strings of batteries would not be affected (a dead cell could otherwise completely disrupt the circuit and result in the no output from the batteries until the dead cell was found and removed). Also, if all 12 batteries were wired in series-parallel without bus bars and a cell failed, that cell would then act as a resistor, which could result in a build up of heat that could melt parts of the battery or boil off the electrolyte. By using bus bars, if a cell failed, only one good battery would be acting on the bad cell, instead of the entire battery bank – resulting in much less heat and a much lower risk of damage to adjacent batteries.
Another reason we chose to use bus bars was to extend the life of our batteries. Because the cells will age differently from one another over time each battery will begin to take a charge slightly differently from it’s neighbor. Bus bars allow each set of two batteries to receive roughly the same charge current because each set has a direct line to the charger – the current does not have to pass through several batteries, encountering varying degrees of resistance along the way, to reach the battery that would otherwise be in the middle of the string.