Bus bar wire gauge

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Mar 26, 2020
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7
I ordered a ton of modem batteries from battery hookup, and I'm finally seeing the light at the end of the tunnel with getting them all tested for their capacity.

I'm planning on building two 14s80p batteries (I may combine each pack so they act like 14s160p) - regardless, I'm trying to calculate the bus bar size.

I have a PIP3048 inverter, so I'm hoping to draw a max of 3000w from the pack.

My calculation for the amps needed are as follows:
PIP 3048 3000w
Efficiency 92%
Each bank lowest voltage 3v = 42v for the entire battery

Total watts (factoring in the efficiency of the inverter if it is outputting 3000w)
3000*((1-.93)+1) = 3240w

3240w/ 42v = 77 amps

From wire charts I've seen a safe gauge of wire for 77 amps of power would be about 4-3ga

Do my bus bars need to be that thick? Or do I attach the heavy gauge wire to the top most positive/negative side of the battery? I was thinking of using 6ga solid copper wire, and spinning that on a drill to make it twisted - will that be enough?

Thanks in advance!
 

Korishan

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Jan 7, 2017
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That's why a lot of ppl use 10-12 awg and triple strand it to make the bussbar. 12awg is good for 20A, and 3 together is 60A. Bursts of 70A would be fine. Strand 3x 10awg for 30A each and you can get 90A capacity w/o issues.

To answer the question directly, yes, yes you do need it that thick if you intend to pull 80+% of rated inverter capacity. One of the methods some people do is a tapered bussbar. They start off with say 3x 10awg, then 1/3 down the pack drop off to 2x strands, then 2/3 down the pack drop to 1x strand. This allows to save on copper and weight, and time to work with it (harder to solder to 3x strands than 1x)

From pack to pack, you'll probably want to use 2 awg welding wire. Not only can it handle the high amps for sustained periods, but it also is very flexible. Makes wiring up packs together a lot easier.
 
Joined
Mar 26, 2020
Messages
7
Very useful stuff, thank you!

Ok so my suspicion is correct that I need to get the wire gauge correct here. If I use a 2 AWG welding wire it is OK crimping/soldering that to a smaller wire from the bus bar?
I was going to use one of the methods I saw on YouTube by HBPowerwall where I will lay the packs next to each other, crimp / solder cable lugs to the end of the bus bars, then bolt them together. But there are going to be places where I need to span a greater distance than next to each other so I think I should use the welding wire there, great tip!

Great idea of buying it already twisted!

What are peoples thoughts on using aluminum for the bus bar, at a higher gauge? Looks like I can buy 4 AWG aluminum wire for almost a third the price of the 6 AWG copper wire: https://www.wireandcableyourway.com/4-awg-rose-aac-bare-aluminum.html
 

OffGridInTheCity

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Dec 15, 2018
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1,264
I find that 2AWG lugs -https://www.amazon.com/gp/product/B073CKHD9C/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
will allow you to combine 2 x6AWG (of twisted copperwire above) .. and crimp nicely.

image_lyhqsc.jpg


Several of us use a crimper like this- works great with 2AWG lugs above -https://www.amazon.com/gp/product/B00KS4R3PI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 It will 'barely' do up to 4/0 wire lugs (onto 4/0 AWG welding wire) :)
 

JCUK

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Nov 1, 2018
Messages
4
I have a question regarding bus bar material.
A neighbour is cladding their house in zinc. They have large off cuts and Im wondering if I can use this as bus bar rather than using striped and twisted household wire, or smashed down copper pipe.
The zinc thickness is a couple of mm.
Any ideas or recommendations?
 

OffGridInTheCity

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Dec 15, 2018
Messages
1,264
JCUK said:
I have a question regarding bus bar material.
A neighbour is cladding their house in zinc. They have large off cuts and Im wondering if I can use this as bus bar rather than using striped and twisted household wire, or smashed down copper pipe.
The zinc thickness is a couple of mm.
Any ideas or recommendations?
Don't have any idea about thickness/shape vs amps... but I would also ask (thinking out loud) will you be able to solder or spot-weld to it? - e.g. you've got to be able to connect thecells to 'zinc' buss electrically - and you don't want it to be difficult :).
 

gauss163

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Jun 28, 2020
Messages
284
BarkersRandomProjects said:
What are peoples thoughts on using aluminum for the bus bar, at a higher gauge? Looks like I can buy 4 AWG aluminum wire for almost a third the price of the 6 AWG copper wire: https://www.wireandcableyourway.com/4-awg-rose-aac-bare-aluminum.html

A problem with aluminum (vs. copper) busbars is it has a much lower melting point: 660C (1220F) vs. 1084C (1983F). If a thermal event causes an aluminum busbar to melt it mayflow into areas that maycause (further) shorts - increasing the chance of thermal runawaychain-reactions.

For example, this is what occurred in a 2012 fire in a 500KW, 1.5 MWh Lithium-ion Battery Energy Storage System (BESS) designed and built by Electrovaya (EV) and installed for Arizona Public Services Company (APS) at an Elden substation in Flagstaff, Arizona. In a root cause analysis document PPI = Performance Improvement International wrote:

PPI said:
As the fire spread from Cell #3 to its surroundings, the heat rose and the aluminum buss due to its relative low melting point (as compared to copper) started to partially melt and flow, causing ground shorts upon contacting the BESS structure. The melting of the buss above the burning cells made contact with the structural frame. This caused ground faults sending high buss currents into neighboring fully charged cells within the cabinets and the neighboring cabinets which accelerated the fire spread between cabinets. If the buss bars were placed at the bottom of the cabinet, this fire may have been limited to Cabinet 7.
 
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