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200 amp rated bus bars... can i double up on the included stock bbs?

Steve Dally

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So I'm reconfiguring my battery to build it up as a 2p4s 560ah total... I will have loads of up to nearly 200 amps (I'm using the Radio B tech 4s 200 amp BMS), but I'm just now realizing/suspecting that the standard bus bars that come with the battery cells (ninthcit 280 ah, in my case) are not up to the task. Can I double up on the bus bars, using two of them for each of the connections, or do I need to get bars properly sized for my application? I suspect the answer to this is that I need to upgrade to a properly sized bus bar, so my next question is where do I find them? I have seen some DIY videos, using 1/8" 110 copper bar, but I don't have a drill press, making the slotted holes a little difficult... any insight here?
Thanks in advance
 
You would actually have more surface area stacking 2 bus bars than one single thicker bar (same logic like wire with many smaller stranded wires in it vs a solid core wire, electrons flow along the outside of the conductor), I would think stacking two would even be a benefit for current over a single bar (my personal opinion). You would need longer studs too...

You could either buy prefab bus bars off AliExpress or eBay or something, or you could buy solid copper strip stock and cut/drill your own. In a mobile application I'd prefer flexible bus bars, and making sure cells are bound good together so they can't vibrate and wiggle, weakening the stud bosses.
 
You would actually have more surface area stacking 2 bus bars than one single thicker bar (same logic like wire with many smaller stranded wires in it vs a solid core wire, electrons flow along the outside of the conductor), I would think stacking two would even be a benefit for current over a single bar (my personal opinion). You would need longer studs too...

You could either buy prefab bus bars off AliExpress or eBay or something, or you could buy solid copper strip stock and cut/drill your own. In a mobile application I'd prefer flexible bus bars, and making sure cells are bound good together so they can't vibrate and wiggle, weakening the stud bosses.
Flexible? As in jumpers built of cable and Lugs? Seems like the 'spring action' of the cables would put constant stress on the studs... I'm maybe not visualizing it correctly, but short jumpers of thick cable seem like a stiff spring, unless I could find ultra pliable cable... Is that the thinking?
 
Well, cables and lugs is one way to get flexible... But my bus bars are solid 'looking' (like wide and flat), but there is some kind of weird hinge in it (I can't see exactly how it works, because it has the black shrink-wrap covering the middle section), but it is bendable, like with pivoting ability. The last kind I've seen are the flat woven mesh material like braided, with lugs on the ends...

I'll see if I can get a pic of mine...
 
Here is a couple pics of my two different types anyways, both of these types I have bend in the middle...

My 12v pack:
1639890198550.jpeg

My 48v packs:
1639890310918.png

Both of these types have some kind of hinge in the middle section under the black covering, so they can bend. The first type is more of a flexible material, where the second picture it actually has some kind of solid hinge mechanism in it (it can bend to a Z shape even).
 
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Okay, those sound perfect! I'm on the search now! Thanks for the input! Are yours rated for 200 amps do you know?

No idea on the amperage rating. As you can see on the top picture, my 12v incorporates 2 BMS (4s2p) so I am only going to pull about half the current as you per each pack on the bank.

I didn't really prefer the idea of going 2p4s because it's harder to know if one of the cells is having a problem because the other cell can take the brunt and mask the symptoms somewhat.

I preferred the concept of each cell having its own BMS lead on it for more granular monitoring. That's just me though. Plus with 4s2p I don't have to worry about amps so much (like if connections aren't absolutely optimal, say they get a little corroded with time or something)...
 
You would actually have more surface area stacking 2 bus bars than one single thicker bar (same logic like wire with many smaller stranded wires in it vs a solid core wire, electrons flow along the outside of the conductor),
Skin effect is in play only for AC, and standard stranded wire offers no advantage. Only Litz wire can help.
 
You would actually have more surface area stacking 2 bus bars than one single thicker bar (same logic like wire with many smaller stranded wires in it vs a solid core wire, electrons flow along the outside of the conductor), I would think stacking two would even be a benefit for current over a single bar (my personal opinion). You would need longer studs too...

Echoing what @tigerwillow1 said, my understanding is that skin effect applies only to AC, not DC.

The stacking of bus bars does indeed result in higher ampacity than a single bus bar of the same aggregate cross section. Within the link below you can find:
A single 1/4" thick, 2" wide bus bar has a 731 amp rating.
A single 1/2" thick, 2" wide bus bar has a 1088 amp rating.
Two 1/4" thick, 2" wide bus bars stacked has a 1301 amp rating. Note that it is not double the 731 amp rating.


Don't ask me for a definitive answer that explains this. Check out footnote #1 at the bottom of the page that indicates space between the bus bars is necessary for that ampacity rating. If we put two bus bars directly into contact with each other, does that imply an even further reduction in ampacity due to an inability to shed heat? Footnote #2 seems to agree with this idea, but I'm not sure if the second rating applies to direct contact bus bars with no spacing at all.
 
Ok well I guess I was wrong then. I was actually taught that in school, in the electrical class of tech school (for automotive), that stranded wire was used in lower voltage (higher current) application on vehicles because electrons flow on the outside of the copper, and thus more surface area with stranded wire, etc. So I guess they taught me wrong.

My apologies if I was wrong. I honestly thought it was the case. So I guess it's a mystery then why 2 bus bars stacked will have higher ampacity than a single thicker one.

(feeling very confused)

I guess I have to read some more, I'll check out that article and footnotes, thanks... :geek:
 
When you figure it out, let me know.
popcorn.gif
 
HA! Silly me, thinking that there was any such thing as a simple question... ?
So now I'm looking at flexible and braided bus bars (installation is in a 4x4 that sees a lot of serious vibration... jarring would be more accurate). Seems more difficult to calculate amperage rating, given the lack of dimensions. Any suggested suppliers, who might advertise amp rating and sell small quantities?
 
Ok well I guess I was wrong then. I was actually taught that in school, in the electrical class of tech school (for automotive), that stranded wire was used in lower voltage (higher current) application on vehicles because electrons flow on the outside of the copper, and thus more surface area with stranded wire, etc. So I guess they taught me wrong.

My apologies if I was wrong. I honestly thought it was the case. So I guess it's a mystery then why 2 bus bars stacked will have higher ampacity than a single thicker one.

(feeling very confused)

I guess I have to read some more, I'll check out that article and footnotes, thanks... :geek:
Thank you so much for all the thoughts on this! You've been of tremendous help!
 
Thank you so much for all the thoughts on this! You've been of tremendous help!

Sure no prob...

Now when I Google it, they say that stranded wire is used in automotive application, because it maintains better tensile strength, handles shorter radius bends easily, and handles the repeated flexing and vibration better. So go figure, I guess I gotta learn some more and get my facts straight hehe...

Looking at this site is really confusing to see the plethora of different opinions on how it works:

(including (but not limited to), the theory of skin-effect I had mentioned)

Oh well, I guess it's not that important to know the why here for me, just that there are a lot of varying thoughts on it.
 
HA! Silly me, thinking that there was any such thing as a simple question... ?
So now I'm looking at flexible and braided bus bars (installation is in a 4x4 that sees a lot of serious vibration... jarring would be more accurate). Seems more difficult to calculate amperage rating, given the lack of dimensions. Any suggested suppliers, who might advertise amp rating and sell small quantities?

Yeah and the other thing. About clamping (since you are using in a mobile application), see my 12v battery pic above, notice the aluminum plates clamped together using threaded rod (more pics on my dedicated picture thread for it: https://diysolarforum.com/threads/pictures-battery-bank-clamp-assembly.22280/ ), a battery bank clamp of some type is really good for a mobile use application.

I've seen some make clamps using wood boards too, but something to keep the cells tight, keep them from wiggling around in relation to each other, then the flexible bus bars are more like, just for micro-movements.

Main reason I chose aluminum is because I could include the plate on the bottomside of the cells and use the heat pad idea (heat dissipates out across aluminum evenly), for the heating option for when temps hit below freezing (since charging below freezing damages LFP cells)...

I just had cut2sizemetals.com make the plates to the sizes I wanted and shipped them...

For reference, these were my dimensions for all of my banks, the 12v was 4-cell long while the 2x 48v banks were 8-cells long (that list shows all of them)...

The first one is the qty:2 bottomside plates for the two 16-cell (longer) 48v packs of mine, the second is the qty:1 bottomside plate for the 8-cell (shorter) 12v pack seen in above pic, the last one is the qty:6 end plates which are compatible size for all of the banks (use 2 of them per bank/pack, on each end)...
1639940041136.png

Or could potentially use wood as some have done...
 
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I used a flat flexible bar rated at 250amps and ran diagonal, I plan on scanning them with a infrared cam to look for loose connections/hot spots at high amp draw. I clamped my cells with 160lb die springs and because they are being installed in a work truck that travels to remote building sites I am mounting them on vibration dampers.
 

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Thanks, I got the buss bar from Galco.com, it was about $100.00 shipped for 79” if I remember correctly. I just cut and drilled it. I was able to make two 280ah batteries with about 10” left over.
 
The wikipedia article on skin effect is fairly good. After the 1st few paragraphs it gets pretty deep into the weeds of theory. Note that the skin depth in copper at 60 Hz. is ~8.5mm, so with 60 Hz power it's a total non-issue unless you're working for the power company or some huge scientific/industrial installation.
 
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