Copper Bus-bar

[n1866878]

Hey there,

We're making a 13s14p battery composed of a 6s14p pack and a 7s14p pack. After doing some rough calculations, we think that we need two copper bus-bars capable of carrying a peak of 150A current in each with a nominal of 50A each at all times. It's for an electric go-kart.

We're looking at something like this to use:
https://www.ebay.co.uk/itm/Copper-Flat-Bar-3-8-1-2-5-8-3-4-2-X-1-8-AND-25mm-30mm-X-3mm/272902420518?var=572085049958&hash=item3f8a407826%3Am%3AmxoY_Ck-bixiFDhRIf8Zl5Q

My question is - Q1: Do you have any advice on what size we should be getting? and Q2: Can we just use a standard drill to drill 8mm diameter holes into these in order to make the + and - terminals for the cables? (my cable lugs have 8mm holes on them)

 

[spinningmagnets]

Common wire has a round cross-section, but when engineering, the current carrying capability is measured in the area of squared millimeters.

For instance, the common 12-ga wire is around 2.05mm in diameter.

the area is the radius times the radius, then times 3.14. (1.025 X 1.025 = 1.05...times 3.14 =) 3.3mm squared

Once you calculate the cross-sectional area of the copper bar, you can use the included chart link to see what size wire the bar is equal to. Then, you can easily find charts that show the current-carrying capability of that bar.

https://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html

 

[teklektik]

This sounds like two batteries with stud terminals (?). If so, I would not use solid busbars because of issues of vibration and minute relative motion in the batteries. Strain on the battery terminals and/or loose connections will almost certainly result. It's a vibrating, flexing, twisting vehicle after all....

Use stranded cable with properly crimped copper ring connectors.

Look at a standard wire chart for chassis wiring ampacity and figure out what gauge will do based on current and the length of the run.

 

[n1866878]

This sounds like two batteries with stud terminals (?). If so, I would not use solid busbars because of issues of vibration and minute relative motion in the batteries. Strain on the battery terminals and/or loose connections will almost certainly result. It's a vibrating, flexing, twisting vehicle after all....

Use stranded cable with properly crimped copper ring connectors.

Look at a standard wire chart for chassis wiring ampacity and figure out what gauge will do based on current and the length of the run.

I don't quite get you. The two packs are being made out of around 184 cells which will individually be spot welding to nickel strips. Our plan was to drill holes in the copper bus-bars and then attach lugs like this

onto the end of the wires (by a hydraulic crimper) and then use a 6mm screw going through the lug and screwing into the 6mm holes we make on the copper bus-bars.

EDIT: wait, are you suggesting that we don't use a solid copper bus-bar but instead use un-insulated copper wires?

Are you sure we can't just use bus-bars? This project isn't meant to be a full-time vehicle. We have a maximum drive time of about 20-30min. And after that, we need to remove the entire battery to recharge it so basically, we would be re-screwing it in every time we need to recharge.

 

[n1866878]

Common wire has a round cross-section, but when engineering, the current carrying capability is measured in the area of squared millimeters.

For instance, the common 12-ga wire is around 2.05mm in diameter.

the area is the radius times the radius, then times 3.14. (1.025 X 1.025 = 1.05...times 3.14 =) 3.3mm squared

Once you calculate the cross-sectional area of the copper bar, you can use the included chart link to see what size wire the bar is equal to. Then, you can easily find charts that show the current-carrying capability of that bar.

https://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html

SpotWeldCopper2.png

Fantastic! Just wondering, once I get the area in squared mm for my copper bar, do I look for wire-current charts with single stranded copper or multi strands? Single stranded right? Since the copper bar is just one big strand really?

 

[spinningmagnets]

There's a thing called skin effect, and it's one of the reasons high current wire is usually a bundle of fine strands. There's very little air between the strands, so look at the amp carrying ability of both stranded and solid, see how much of a difference there is.

I always try to go extra fat on wires, so I've never really calculated the exact size of wire needed. Because of that, I don't know which charts are the most accurate...

 

[999zip999]

Look at R/C type 12ga 10ga or 8ga 1,000 strain wire high current and flexible.