Questions about bus bar sizing

[ericfx1984]

So I'm really trying to understand best bar sizing... I've seen a couple different ways to look at it

Some people say that you need to look at what your maximum current of all items put together could possibly add up to

Other people say you need to keep in mind which direction current is traveling

So for instance if I'm hooking four batteries together on a bus bar and each battery can deliver 200 amps... Well altogether that's 800 amps so one would think that I need a bus bar that can hand at least 800 amps

Then we take it a little further...

My loads will be for inverters at 130 amps a piece (according to manufacturer)... That's about 520 amps

In theory the batteries should never deliver more than 520 amps to the four inverters

So would I be safe then with a bus bar rated for say 600 amps since in theory I should never be pulling more than 520 amps? Or I could even pat it at something rated for 7 or 800 amps

Or would it be more important to look at the maximum current that the batteries can deliver (limited by BMS)

 

[ericfx1984]

But then there's another thought... Do I really need to carry the full load of all the inverters or even of all the batteries for that matter?

Let's say that I have a bus bar that is rated for say 300 amps, so, 50mm wide and 5mm thick...

And theory if I placed The battery terminal of battery 1 right across from inverter 1, and battery 2 across from inverter 2 and so on

I should never see more than 130 amps across any section of the bus bar...

I wonder would this cause some problems with current sharing between batteries/inverters?

 

[DIYrich]

From a "safety" standpoint, I would size it for the maximum inverter draw. If you ever have a fire, the Insurance Company can't ding you for having undersized equipment.

By interweaving the batteries and inverter connections, that gives you an additional "safety margin". Size for 520 amps (650 amp bar - 80% rule?), but only use 130 amps across any individual segment during "normal" usage.

Note: Batteries could drop out, and batteries on one side of the bar supply power to inverters in the middle/other side of the bar.

 

[ericfx1984]

From a "safety" standpoint, I would size it for the maximum inverter draw. If you ever have a fire, the Insurance Company can't ding you for having undersized equipment.

By interweaving the batteries and inverter connections, that gives you an additional "safety margin". Size for 520 amps (650 amp bar - 80% rule?), but only use 130 amps across any individual segment during "normal" usage.

Note: Batteries could drop out, and batteries on one side of the bar supply power to inverters in the middle/other side of the bar.

Appreciate it. I think this makes more sense. Thank you so much for helping me confirm what I was thinking... It almost makes me want to overbuild it a little further and have a huge safety margin