Module Busbars - EMS Sigma Clad 60

Our busbars are made from EMS Sigma Clad 60 material. There is a center core of copper (60% of the material) then stainless steel and nickel layers on the outside.

Material Details

The inner copper layers allow for the high conductivity and low temperature rise when the current flow is lateral, across the material, which the nickel and stainless steel layers increase the resistivity of the material when current is flowing vertically, as is the case with a spot welding procedure. This increase in resistance for vertical conduction allows the material to heat up when large currents are passed through it. If a large enough current is passed through it, the material will melt and successfully create a welded joint to other surfaces. In our case, these 'other surfaces' will be the 18650 cells and the nickel strips.

Use

INSERT PICTURE OF LOCATION ON MODULE AND PLAIN PARTS

These busbars will carry the large currents that will be going through our battery pack. We are designing for these busbars to carry up to 100A without significant temperature rise (ideally under 10 to 15 degrees C). Being electrically and thus thermally connected to the battery cells, the busbars act as a small heat sink to carry heat away from the material, but more importantly, they conduct heat through themselves. We have added a thermal pad on the bottom of the module to conduct the heat from the busbars (and thus the cells) away from the modules into the catamaran of the car where it is dispersed thanks to the high planar thermal conductivity of carbon fiber.

The tabs with holes will connect the modules in series, with the help of M4 nuts and bolts, washers, disc springs, as well as electrically insulating sleeve washers. These tabs must be bent up so that when two opposing modules are in place, their adjacent tabs can be bolted together.

On the other end of the busbars, we have voltage taps. These provide a voltage measurement of the module that is out of the path of current flow. Our AFEs measure the voltage of the cells at these points. Because they are not in the path of current flow, there is no voltage drop across them thanks to Ohm's law (V = IR), so we are measuring the voltage at the cell more accurately. On the bottom busbar, the voltage tap is found in the middle. In this position, it is in the path of current flow, and thus we do measure the effect of a small voltage drop as well. However, the wiring is simplified as we then do not have wires crossing all over the modules.

The next revision of the modules will have 2 wires coming off of such tabs in order to enable online internal resistance measurements of the cells. 

Amount Required

show calculations

Roughly 30 square feet.

Source for Material

Direct from EMS through EMS's university program

Manufacturing

Water jet cutting (not laser due to potential dangers of reflection) - most of the laser cutters that we talked with did not want to cut it because of this, but a few of the manufacturers in the US that EMS have previously worked with would laser cut it for us, though the quotes received from them were on the order of $1500-$3000 - way out of our price range.

Once we get the water jet parts back, we will need to bend the voltage taps (by hand) and bend the series connection tabs using a jig to achieve a precise radius - the jig will need to bend the material further than the end angle to account for bend relaxation.