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Old 10-04-2021, 02:08   #1
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Bus Bar Size Determination

OK So building the Lithium Bank in 4P4S 16 x 3.2v 280Ah



For the Parallel I am using Anodised Aluminum which is 4mm x 16mm x 90mm -



Now for the series connection I would like to know if I can use this same size with a single bus bar connecting each Parallel to Series.



In total at a maximum I could have up to 200 Amps flowing out into the inverter.


So how do I figure out if its OK for the Parallel and OK for the serial connections?


Hope that makes sense
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Old 10-04-2021, 02:55   #2
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Re: Bus Bar Size Determination

Anodising on aluminium has poor conductivity. That is normally one of the advantages. At least remove the anodising around each of the connections.

Copper bar is readily available and would be a better choice.
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Old 10-04-2021, 03:07   #3
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Re: Bus Bar Size Determination

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Originally Posted by noelex 77 View Post
Anodising on aluminium has poor conductivity. That is normally one of the advantages. At least remove the anodising around each of the connections.

Copper bar is readily available and would be a better choice.

That's what you get for talking to your 12V Shop specialist that build their own systems!


So if I go copper I take it 16 x 4 will give me up to 255Amp rating or am I reading the following site incorrectly?


https://www.australwright.com.au/tec...busbar-rating/
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Old 10-04-2021, 03:09   #4
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Re: Bus Bar Size Determination

One more question - Is it best to go with straight copper or tin coated?
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Old 10-04-2021, 03:32   #5
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Re: Bus Bar Size Determination

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One more question - Is it best to go with straight copper or tin coated?
IMO, tin coated. The tin is so thin as not to make any difference resistance wise yet protects the copper from future corrosion.
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Old 10-04-2021, 03:44   #6
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Re: Bus Bar Size Determination

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Originally Posted by UFO View Post
... So if I go copper I take it 16mm x 4mm will give me up to 255Amp rating or am I reading the following site incorrectly?
https://www.australwright.com.au/tec...busbar-rating/
You are reading the chart correctly, for Copper busbar.
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Old 10-04-2021, 03:48   #7
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Re: Bus Bar Size Determination

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You are reading the chart correctly, for Copper busbar.

Thanks
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Old 10-04-2021, 07:12   #8
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Re: Bus Bar Size Determination

16 x 4 gives you a cross sectional area of 64mm2.

The closest battery cable is 50mm2. This is sometimes listed as having a current carrying capicity as high as 345A, but a more realistic number is around 175A (this depends on the insulation rating, whether the wire is bundled and whether it leads through an engine space etc).

The busbar does not have any insulation to melt like a wire, but using wire tables gives you a good indication. The busbar needs to be secured to a backing board, possibly a cover and will have wires (with insulation) attached. These will heat up along with the busbar itself

So 16 x 4 will be OK for 200A, but it is going to become reasonably warm. It also does not leave you any room for expansion if you decide you need a higher current device at a later stage. Raw copper bar is not expensive and it is available in a multitude of sizes so personally unless there is compelling reason to keep it small as possible I would go a little larger, say 20x5 or even 30x5 especially if the feed wires are larger than 64mm2 and there is any chance of attaching something like a large inverter at a later stage. It would be a shame to limit future options, or have to replace a busbar.

Tinned copper is better, but is harder to get in custom sizes. Raw copper is commonly used for busbars on boats and is perfectly fine.
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Old 10-04-2021, 09:52   #9
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Re: Bus Bar Size Determination

In. 4p4s the series jumpers are 1/4 current. (So 50a if drawing 200). The parallel will vary based on how the load wires come off and each could be different. between 1/4 and 3/4 current.
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Old 10-04-2021, 10:57   #10
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Re: Bus Bar Size Determination

Are there good online calculators for this?
I am used to seeing ones for printed circuit boards like https://www.4pcb.com/trace-width-calculator.html, that allow a person to input many variables (thickness, width, length, ambient temp, temp rise, insulated or not), but I understand that they extrapolate after a certain number of amps or copper thickness that are well below 'bussbar' range.
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Old 10-04-2021, 11:40   #11
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Re: Bus Bar Size Determination

Should you use raw copper, you can DIY tin it after fabrication.
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Old 10-04-2021, 12:13   #12
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Re: Bus Bar Size Determination

I use 30 x 15 plain copper bar it's more than enough and it's easy to get. I always have a couple of spares with me.
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Old 10-04-2021, 13:07   #13
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Re: Bus Bar Size Determination

Silver flashed copper is even more corrosion resistant than tin. Online metals.com had it for a while and it was cheaper than tinned. The silver flashing is very thin.

I would suggest that you heatshrink over the buss bars with cutouts where needed. Dropping a tool on an uninsulated buss bars would be very bad.
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Old 10-04-2021, 17:54   #14
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Re: Bus Bar Size Determination

Quote:
Originally Posted by noelex 77 View Post
16 x 4 gives you a cross sectional area of 64mm2.

The closest battery cable is 50mm2. This is sometimes listed as having a current carrying capicity as high as 345A, but a more realistic number is around 175A (this depends on the insulation rating, whether the wire is bundled and whether it leads through an engine space etc).

The busbar does not have any insulation to melt like a wire, but using wire tables gives you a good indication. The busbar needs to be secured to a backing board, possibly a cover and will have wires (with insulation) attached. These will heat up along with the busbar itself

So 16 x 4 will be OK for 200A, but it is going to become reasonably warm. It also does not leave you any room for expansion if you decide you need a higher current device at a later stage. Raw copper bar is not expensive and it is available in a multitude of sizes so personally unless there is compelling reason to keep it small as possible I would go a little larger, say 20x5 or even 30x5 especially if the feed wires are larger than 64mm2 and there is any chance of attaching something like a large inverter at a later stage. It would be a shame to limit future options, or have to replace a busbar.

Tinned copper is better, but is harder to get in custom sizes. Raw copper is commonly used for busbars on boats and is perfectly fine.

Duly noted - I will upsize
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Old 10-04-2021, 17:54   #15
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Re: Bus Bar Size Determination

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Originally Posted by smac999 View Post
In. 4p4s the series jumpers are 1/4 current. (So 50a if drawing 200). The parallel will vary based on how the load wires come off and each could be different. between 1/4 and 3/4 current.

Thanks for that
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