Busbar calculate dimension

M1kkel

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Nov 16, 2019
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Hi there.
Been prototyping a busbar made from 16mm2 strained copper, but the strained copper is difficult to work with.
Now, I was trying to calculate the wire size using stiff copper wire, for example 3x4mm2 twisted.
So how do you calculate it?
what I mean is, I have two wires going down the length of the pack consisting of 3x4mm2 that’s a total of 24mm2, on the positive side and also on the negative side. Total of 48mm2.

using this calculator i will need 50mm2. https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator

however watching many YouTube videos they don’t even use this wire gauge - so maybe I’m miscalculating something.

im calculating a 48volt system, 3% loss, wire length 1 meter, 200 amp and that gives me 50mm2 wire gauge. Can’t get my head around it, is the 200amp for the entire 14 packs? The current will run through all packs, so I assume it’s 200 amp for each..

Help me 😫😫

by the way, see my prototype on strained copper busbar.
I have also attached a picture of the underground bunker that i build for my batteries. The wife thinks I’m an idiot. 🤷‍♂️
 

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Korishan

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Yes, amps runs the entire length of the battery (all packs in the string), not just the packs at the ends.

50mm2 is 1AWG (for us non-metric ppl). That's about the right size. Something to consider, though, is that you won't be running 200A continuous. You'll only peak around there during inverter surges or short times when the charger is engaged.

I think Peter used close to that size when he built his packs. Something to consider, is that you only need that size wire for the interconnects, not the bus bar itself. The bus bar is usually spread out. So if you have 2 runs, you'd only need 2x 25mm2 runs, that connect to a common point that then goes to 50mm2. Or, if you have 3 runs, then they'd be 16mm2. The large wire only is needed between packs.
 

OffGridInTheCity

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Dec 15, 2018
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I think its an amazing bunker... absolutely love the concept and has gotten me thinking!. The remaining large project at my house is an outdoor shed for my wife's gardening equipment. A perfect place for a bunker or at least an under-floor vault? - it would be out of sight... and maybe I can sell it :)
 

M1kkel

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Nov 16, 2019
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18
I think its an amazing bunker... absolutely love the concept and has gotten me thinking!. The remaining large project at my house is an outdoor shed for my wife's gardening equipment. A perfect place for a bunker or at least an under-floor vault? - it would be out of sight... and maybe I can sell it :)
Just do it! I think it’s so cool! 😂
 

M1kkel

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Nov 16, 2019
Messages
18
Yes, amps runs the entire length of the battery (all packs in the string), not just the packs at the ends.

50mm2 is 1AWG (for us non-metric ppl). That's about the right size. Something to consider, though, is that you won't be running 200A continuous. You'll only peak around there during inverter surges or short times when the charger is engaged.

I think Peter used close to that size when he built his packs. Something to consider, is that you only need that size wire for the interconnects, not the bus bar itself. The bus bar is usually spread out. So if you have 2 runs, you'd only need 2x 25mm2 runs, that connect to a common point that then goes to 50mm2. Or, if you have 3 runs, then they'd be 16mm2. The large wire only is needed between packs.
I actually looked at Peters video’s, and thought they looked thin.

So you say 25 amp’s per run, if I have 2 strings on each side, that’s four in total, so only 12,5 per twisted copper wire?
OR is it 50 amp on the positive AND negative side ?
 

Korishan

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I actually looked at Peters video’s, and thought they looked thin.

So you say 25 amp’s per run, if I have 2 strings on each side, that’s four in total, so only 12,5 per twisted copper wire?
OR is it 50 amp on the positive AND negative side ?

The main terminals on the pack, the ones that connect to the other packs, are the full size as they carry the full the load. However, the runners are split across the pack.

In your images you show a pack that has two 2 runners. Each of these need to be only had rated for half of the max. But, when they merge into a single wire to go to the next pack, that single one needs to be the sum of the two.
So for a pack designed with all positive on one side, and negative on the other, you would have a total of 4 runners and 2 leads.

Something you could do is take a single large wire, strip it for the length of the pack, split the bundle in half, and then run 1 half for each runner. This would minimize any extra soldering or need for extra wires.
 

Wolf

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Sep 25, 2018
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I have also attached a picture of the underground bunker that i build for my batteries
I like it.
Well in this instance I may have to agree with your wife.:sneaky:
By the way the the bunker was constructed and the dewalt concrete saw, also various mason tools scattered about, I would assume you are a professional mason and know how to do these things. The thing that convinced me the most was the Tuborg beer as I know of no bricklayer/ mason that doesn't drink beer.:p All masons drink beer but not all beer drinkers are masons.
1617707780699.png1617707908992.png
With all the drinking and venting I'm assuming condensation, humidity, the water table, flooding, rain, and the occasional dike breach( I extrapolated the location from the beer can, tell me I am wrong) has been taken into account. I am sure it has, as the "bunker" looks quite professionally built.
I like it.

Now the soldering skills need to have a revisit. Not enough beer I mean heat on those joints. Definitely need a bigger soldering iron to heat those connections up quickly and get a good solder joint. This is where you would need a battery bunker for as these type of joints would cause heat and possibly a melting scenario with glowing things. Maybe have a plumber show you how to sweat a joint and watch how solder flows at the right heat.
Wolf
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Redpacket

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Feb 28, 2018
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+1 like Korishan said above, you don't total the plus cable & the minus cables sqmm for current calcs.
It's just pick either one & use that sqmm (this is the sum of all the cables on the plus side (or minus)).
You might want to split the "incoming" plus or minus cable total sqmm out more across the surface of the pack like you have with the fat cables but maybe use eg 4 cables & more attachment points but still summing to the one plus (or minus) connector.
200A at nominal 48V system is approx 10kW. Is this going to be your sustained load eg for more that a minute or so?
I'd focus on resistance & safe current ratings at your typical load kW number.
Short term current rating (eg 30secs of overload) still need to be considered to of course.
 
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ajw22

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Nov 16, 2018
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573
Now the soldering skills need to have a revisit. Not enough beer I mean heat on those joints. Definitely need a bigger soldering iron to heat those connections up quickly and get a good solder joint.
Yes, those solder joints definitely look like the weak points, and will heat up for sure. Add to that the missing strips (yellow circles) at the critical areas, creating choke points (red circles). It's just a tiny bit of nickel strip, but I'm sure it'll go a long way to make this pack 200A ready.
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