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Bus bar wire gauge
#1
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 PIP 3048 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!
hbpowerwall likes this post
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#2
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.
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#3
Agree with @Korishan - I use this:
(6 AWG Soft Drawn, Stranded, Bare Copper Wire)  https://www.wireandcableyourway.com/6-aw...-wire.html
to avoid manually twisting wire myself Smile    A 100w iron solders to this nicely.    
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#4
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 people’s 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-aw...minum.html
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#5
I find that 2AWG lugs - https://www.amazon.com/gp/product/B073CK...UTF8&psc=1
will allow you to combine 2 x 6AWG (of twisted copper wire above) ..   and crimp nicely. 


Several of us use a crimper like this - works great with 2AWG lugs above - https://www.amazon.com/gp/product/B00KS4...UTF8&psc=1              It will 'barely' do up to 4/0 wire lugs (onto 4/0 AWG welding wire)  Smile
Barkers Random Projects likes this post
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#6
I have a question regarding bus bar material.
A neighbour is cladding their house in zinc. They have large off cuts and I’m 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?
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#7
(08-03-2020, 09:31 PM)JCUK Wrote: I have a question regarding bus bar material.
A neighbour is cladding their house in zinc. They have large off cuts and I’m 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 the cells to 'zinc' buss electrically - and you don't want it to be difficult Smile.
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#8
Thanks everyone I bought that 6ga copper wire from www.wireandcableyourway.com some 2 ga welding wire, that hydrologic crimper, and an assortment of lugs. I have some large heat shrink, hope it fits!
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