[smbevma]

Hi:

Originally I thought I could connect these negative "-" wires all in one place but that is not practical. I see posts and busbars on ebay/ Amazon but they are only rated for 48 volts DC, I'm running a 72 volt system.

Does anyone have any suggestions? I've attached an example of what I was thinking of, but it is only rated for 48v. thanks

 

[floydr]

A busbar of 1/8"-1/4"copper the width determined by the amps you are putting though the bus bar. As long as you need it to be. I have used this busbar calculator Busbar Current Calculator Online | Electrical4u to calculate the width needed. 1/8"= 3.175mm. Holes drilled for connections
Later floyd

 

[floydr]

OR a butt joint using copper tubing/butt joint the appropriate size and a hydraulic crimper ≥10 ton
Later floyd

 

[cricketo]

A busbar of 1/8"-1/4"copper the width determined by the amps you are putting though the bus bar. As long as you need it to be. I have used this busbar calculator Busbar Current Calculator Online | Electrical4u to calculate the width needed. 1/8"= 3.175mm. Holes drilled for connections
Later floyd

That calculator is rather strange. Say I'm using 3/4" x 1/8" copper bar in my battery projects. That is 19.05 x 3.175 mm. Per calculator, such bar would have capacity of 72.6A. At the same time, 19.05*3.175=60.5mm2, which is in between 1/0 and 2/0 wire, and say 1/0 wire is typically rated up to 280A or so, which also takes into account the insulation rating.

Maybe I'm missing something, still on the first cup of coffee

 

[remy_martian]

Bus bar calculators assume natural convection air cooling, not merely cross sectional area. So they are nonlinear. But the current does seem low....they must be factoring drilled holes.

 

[cricketo]

Bus bar calculators assume natural convection air cooling, not merely cross sectional area.

But, yes, 72A sounds low

So maybe heat dissipation is taken into account ? Sort of if you want to keep it at ambient temp, don't pump more than X amps. But we don't usually take such consideration into account for the wiring - there we just don't want to melt/light up the insulation.

 

[smbevma]

This will work perfectly. I'll make some on my CNC. Thanks!

 

[remy_martian]

You're in for a treat if you've never machined copper before...

 

[floydr]

I forgot to mention that the calculator is very conservative by a 1/3rd or more.
later floyd

 

[remy_martian]

It seems to be set up for touch temperature, which would be weird as a precaution because with most bus bars you'd get electrocuted before you'd realize you got burned 😂

 

[smbevma]

You're in for a treat if you've never machined copper before...

I'll make them out of 1/4" aluminum

 

[cricketo]

What grade of aluminum ? I haven't checked, but I suspect common machinable grades such as 6061 aren't actually great for electrical applications.

Oh, found a nice table :

https://content.ndtsupply.com/media/Conductivity_Al%20Reference%20Chart.pdf

Looks like 61S can be as low as 65% of the pure aluminum's conductivity.

 

[smbevma]

I'm using 6061 and my electrical engineer friend told me it would be fine. I also have an almost limitless supply of it!

 

[cricketo]

Engineers can be full of shit when their ass isn't on the line On the other hand when they're paid to the the job, shortcuts aren't permissible. Long story short, if you're going to use 6061, at least make the bus bar bigger using that conductivity data to compensate.

 

[floydr]

here the formula they use.
"Copper:
Copper busbar current carrying capacity = 1.2 * Busbar width in mm * Thickness in mm Amps"
which is1.2A mm²
"Aluminium:
Aluminium busbar current carrying capacity = 0.8 * Busbar width in mm * Thickness in mm Amps"
.8A mm²
Later floyd

 

[remy_martian]

^^Many can be pretty ignorant as well.

That 1/4" aluminum is equivalent to 1/16th copper, off the top of my head.

Did your alleged "engineering" buddy also tell you what a pain in the ass it is to make a good electrical connection to aluminum? How it behaves when you pass current through it and another metal it is in contact with?

It's the worst choice you could make for adapting 10 gauge to 2 gauge wire, lol. And it's a horrible cell to cell connector, if that's actually your pic you're showing, unless you really know what you're doing.

 

[remy_martian]

here the formula they use.
"Copper:
Copper busbar current carrying capacity = 1.2 * Busbar width in mm * Thickness in mm Amps"
which is1.2A mm²
"Aluminium:
Aluminium busbar current carrying capacity = 0.8 * Busbar width in mm * Thickness in mm Amps"
.8A mm²
Later floyd

Aluminum busbar is a totally different beast to 6061

 

[smbevma]

^^Many can be pretty ignorant as well.

That 1/4" aluminum is equivalent to 1/16th copper, off the top of my head.

Did your alleged "engineering" buddy also tell you what a pain in the ass it is to make a good electrical connection to aluminum? How it behaves when you pass current through it and another metal it is in contact with?

It's the worst choice you could make for adapting 10 gauge to 2 gauge wire, lol. And it's a horrible cell to cell connector, if that's actually your pic you're showing, unless you really know what you're doing.

You've convinced me to take another look at this. I will let you know what I do.

 

[reiderM]

Get some copper flat bar, pretty cheap online. I like metalsdepot.com, always had a good experience with them. Copper is a pain to work with though for sure.

 

[summetj]

Ring terminals crimped with a hydraulic crimper on each wire, and one big bolt, all wrapped in electrical tape?

But yah, a bus bar with separate bolts for each ring terminal would be better....