Busbar calculate dimension

Announcement - Help us fight the BOTS! Please report all spam including stuff in your inbox!

M1kkel

New member
Joined
Nov 16, 2019
Messages
24
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. 🤷‍♂️
 

Attachments

  • 17ED1650-3CEE-4929-9966-C9A46A64955D.jpeg
    17ED1650-3CEE-4929-9966-C9A46A64955D.jpeg
    2.5 MB · Views: 138
  • FC1FF594-CD73-4762-8405-9A698F1FBD0B.jpeg
    FC1FF594-CD73-4762-8405-9A698F1FBD0B.jpeg
    2.3 MB · Views: 130
  • BE2CEACF-8375-4107-9131-AD3D45E89F5B.jpeg
    BE2CEACF-8375-4107-9131-AD3D45E89F5B.jpeg
    2.4 MB · Views: 139
  • image.jpg
    image.jpg
    1.8 MB · Views: 122
  • image.jpg
    image.jpg
    1.6 MB · Views: 145

Korishan

Moderator
Joined
Jan 7, 2017
Messages
6,522
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

Active member
Joined
Dec 15, 2018
Messages
1,708
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

New member
Joined
Nov 16, 2019
Messages
24
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

New member
Joined
Nov 16, 2019
Messages
24
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

Moderator
Joined
Jan 7, 2017
Messages
6,522
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

Active member
Joined
Sep 25, 2018
Messages
1,564
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
1617709430949.png
 
Last edited:

Redpacket

Member
Joined
Feb 28, 2018
Messages
1,289
+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.
 
Last edited:

ajw22

Member
Joined
Nov 16, 2018
Messages
641
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.
1617710741557.png
 

M1kkel

New member
Joined
Nov 16, 2019
Messages
24
+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.

Sorry for the very late reply.
I was calculating for 10KwH peak load in maybe 5-10 minutes. I will lower this calculation, and limit the amount of amperage i draw from my battery. The inverter will top up from grid.
 

M1kkel

New member
Joined
Nov 16, 2019
Messages
24
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.
View attachment 24547
Sorry for the late reply. Thanks for this, you really had a good look. i will do a redesign with tw3isted copperwires, like everyone else. I cant heat this enough up since its 16mm2. I have a 100W soldering iron.
 

M1kkel

New member
Joined
Nov 16, 2019
Messages
24
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.
View attachment 24543View attachment 24544
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
View attachment 24546
Wolf, you really had me lauging here. !! :) This was a funny reply. I really like you tried to extrapolaty my location, but what was your result of the extrapolation then? :)

I live in Denmark, We have heavy rains sometimes. My bunker is build upon a really heavy clay bottom. So thats quite wet, therefore i have build it like it should be in a professional setup.

Im not a mason, im a freaking IT guy :D
We was gonna build a highly insulated shed for the batteries, but the wife and me didnt think it would compliment the house, no matter where we build it on our land. So i told her, "DUCK it, i will build a bunker". Jesus what a project. !!

I will post pictures soon, i have had a corten steel hatch mounted, with gas shock absorbers, as well as a ladder down the hole.

i LOVE tuborg, and ofcourse thats "Made in Denmark"

I see you are absolutely correct about the soldering skills. I therefore purchased a bigger 100Watt soldering iron, but thats not enough to heat up the threaded copper wires. So i have actually decided to build the busbars from twisted copper wires, and i will lower the current to max 100Amp.

I have build the new busbars from 3x4mm2 solid copperwires, 2 strings down the battery on + and - side. I should be able to draw 131 amp max with 24mm2 total.4x3 + 4x3 = 24 mm2. I have used: https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator

However im unsure if me twisting 3 wires equals the same as 1 25mm2 wire.
 

Wolf

Active member
Joined
Sep 25, 2018
Messages
1,564
I really like you tried to extrapolaty my location, but what was your result of the extrapolation then? :)
Denmark aye.
"
I'm assuming condensation, humidity, the water table, flooding, rain, and the occasional dike breach
My assumption was " Netherlands/Holland " so I was wrong but close. But I do understand nationality so forgive me for calling it close. Although even closer "Germany and Austria" but don't call me a German I am an Austrian not a German and don't you forget it. :p
IT you say funny that's what I do. Well in my case Automotive repair is my second fortay when the big EMP hits and wipes all the electronics off of the face of the earth. you will certainly have a good career in foundation and bunker building.🤣


Now to wires and cabling.
Well 4mm2 wire will carry 20A so X3 =60A X2 =120A.
So yes twisting 3 4mm2 solid wires will give you the cross section of a 24mm2 cable.
I personally don't believe that you will be drawing 120A continuously from you battery. Probably ½ that.
Now from pack to pack and to the Inverter you will want to size your cabling according to distance and the highest potential current draw.

I will post pictures soon, i have had a corten steel hatch mounted, with gas shock absorbers, as well as a ladder down the hole.
Patiently waiting on pictures.
Wolf
 

M1kkel

New member
Joined
Nov 16, 2019
Messages
24
Denmark aye.
"

My assumption was " Netherlands/Holland " so I was wrong but close. But I do understand nationality so forgive me for calling it close. Although even closer "Germany and Austria" but don't call me a German I am an Austrian not a German and don't you forget it. :p
IT you say funny that's what I do. Well in my case Automotive repair is my second fortay when the big EMP hits and wipes all the electronics off of the face of the earth. you will certainly have a good career in foundation and bunker building.🤣


Now to wires and cabling.
Well 4mm2 wire will carry 20A so X3 =60A X2 =120A.
So yes twisting 3 4mm2 solid wires will give you the cross section of a 24mm2 cable.
I personally don't believe that you will be drawing 120A continuously from you battery. Probably ½ that.
Now from pack to pack and to the Inverter you will want to size your cabling according to distance and the highest potential current draw.


Patiently waiting on pictures.
Wolf
Denmark is correct 😀

powerwall is up and running, will post a story when I have the time. 🙈
 
Top