RAW Cell Busbar Ampacity

[ChrisG]

Completed a build of two 48v packs made up with 105ah EVE cells. The battery busbars that came with the batteries are 12mm wide by 2mm thick copper. According to the calculator in the link below, the copper bus bars that came with the batteries can only carry just over 28amps. Means this 48v pack is limited to 1.3kw. Is this accurate? I've pulled more than 1.3kw out of each pack and didn't notice any heating but wasn't for a long duration. Feel like I'm missing a component in the math here or maybe this calculator is wrong.

Link to busbar ampacity calc: https://www.allumiax.com/bus-bar-size-calculator

Edit:
This calculator shows that 2mm thick x 12mm wide (1/16" by ~1/2") can do 100 amps.
Link: https://stormpowercomponents.com/te...es/copper-alloy-c11000-busbar-ampacity-chart/

Very confused.

 

[RCinFLA]

Since EVE105 cell are about 36.5 mm wide, I presume the length of bus bar is about 37 mm between terminal bolts.

2mm x 12 mm x 37 mm pure copper bus bar will be about 0.02 milliohms.
Resistivity of 99.99% pure copper (rho) is 0.017 micro ohm-meter.
R_dc = rho x length/area.

Busbars should be nickel plated to prevent copper to aluminum cell terminal intermetallic interaction which will eat at aluminum surface of cell terminal. The nickel plating will raise the busbar resistance about 20%, so busbar yields about 0.024 milliohms.

Each cell terminal compression connection will have about 0.05 milliohms of compression contact resistance. You will have four times the resistance in battery terminals compression connection than busbar itself. This assumes you have a good clean terminal connection to cell terminals. At least clean connecting surfaces with alcohol and dry off. Keep dirty, oily, and salty fingers off of contact surfaces.

Total terminal to terminal resistance will be 0.05 + 0.024 + 0.05 = 0.124 milliohms.

At 50 amps of current there will be 50A x 0.124 milliohms = 0.0062 volt drop, terminal to terminal.

Heating will be 50A^2 x 0.124 milliohms = 0.31 watts per busbar/terminal.

You will not notice any heating at a third of a watt of heating.

Busbar is fine, as long as they are truly copper core and nickel plated.

 

[ChrisG]

Since EVE105 cell are about 36.5 mm wide, I presume the length of bus bar is about 37 mm between terminal bolts.

2mm x 12 mm x 37 mm pure copper bus bar will be about 0.02 milliohms.

Busbars should be nickel plated to prevent copper to aluminum cell terminal intermetallic interaction which will eat at aluminum surface of cell terminal. The nickel plating will raise the busbar resistance about 20%, so busbar yields about 0.024 milliohms.

Each cell terminal compression connection will have about 0.05 milliohms of compression contact resistance. You will have four times the resistance in battery terminals compression connection than busbar itself. This assumes you have a good clean terminal connection to cell terminals. At least clean connecting surfaces with alcohol and dry off. Keep dirty, oily, and salty fingers off of contact surfaces.

Total terminal to terminal resistance will be 0.05 + 0.024 + 0.05 = 0.124 milliohms.

At 50 amps of current there will be 50A x 0.124 milliohms = 0.0062 volt drop, terminal to terminal.

Heating will be 50A^2 x 0.124 milliohms = 0.31 watts per busbar/terminal.

You will not notice any heating at a third of a watt of heating.

Busbar is fine, as long as they are truly copper core and nickel plated.

@RCinFLA they are plated copper and thank you you for the information and calculations above. The first calculation link in my post is what worried me and must be incorrect. Also seems the cross section of the bus bar is equal to about 4awg which according to other sources can do about 86 amps which is what I hit at peak with no noticeable warm areas. I am going to leave pack as is. I made sure surfaces were clean and level. One Busbar had an ‘edge’ on the terminal hole. Just used a deburring tool to clean that up so it layed flat on battery terminal.

 

[RCinFLA]

If you feel heating of bus bars it will likely be due to poor cell terminal connection. Getting a good cell terminal connection is not as easy as it appears. Cleanliness, flatness, and surface area pressure is important.

A strong (thick) top side flat washer helps to distribute pressure on terminal evenly without bus bar 'puckering' at the center relieving pressure at edges of connection interface surface.

It is the cell terminal surface to bus bar bottom surface contact area that matters. Bolt is for pressure, not to conduct current. Stainless steel hardware prevents corrosion.