16S bank layout and bus bar sizing questions

SparkyJJO

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I have 32 cells I'm putting into 16s packs, each with its own BMS. My setup is going to be stationary, although if I need to move things around I want it "relatively" easy to move (not that 160 pound battery bank is ever going to be "easy").

1) Layout.
Having 16 cells in a row would be more messy from a wiring standpoint (wires from opposite ends, longer runs), plus it seems like it would be more awkward to move if I did ever need to. So two parallel rows of 8 cells seems better suited. However, Is there any concern with the one bus bar that links the two rows together being longer than the rest?

1648051016789.png

2) Bus bars.
The bus bars that were provided with the cells are totally wimpy. Max current draw by the inverter would be just under 200A, and this should be split between the two battery packs. Realistically, I won't be pulling near that for any sustained period (for one thing, the batteries would run down awfully fast), but I want to design for worst case scenario. So worst case, if one pack was offline, and I started pulling 200A from one pack, I don't want to overheat the bus bars. What size bar would I be looking at? 1/8" x 3/4"? Or should I go up to 1" wide?

3) Bus bar material.
Pretty clear I would use copper. I was assuming tinned copper (can get from onlinemetals.com). But I have seen people use untinned copper bus bars. Seems like that would be an issue, but is it a non-issue if using noalox? Is that why some have not used tinned copper?
 

HRTKD

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Linking the two rows is no different than linking any other cell in the pack. That's from an amperage standpoint. The length of the bus bar between the two rows is likely going to be different than all the other bus bars. YMMV, check the actual dimensions.

Raw copper against aluminum terminals would lead to galvanic corrosion. A layer of conductive anti-corrosion paste would help. Tinned copper would also help. You could make the bus bars out of aluminum. However, aluminum isn't as good of a conductor as copper. The aluminum would need to be about twice the cross section of copper to handle the same amperage. I have aluminum bar stock that, if I ever get around to it, I'll use to replace the bus bars that came with my cells.

I recommend going with 1" wide flat bar. The reason is that it presents a wider base for a cable lug to sit on if the cable was installed perpendicular to the bus bar. A 3/4" bus bar would have some of the cable lug hanging over the edge.
 
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labeeman

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I have 32 cells I'm putting into 16s packs, each with its own BMS. My setup is going to be stationary, although if I need to move things around I want it "relatively" easy to move (not that 160 pound battery bank is ever going to be "easy").

1) Layout.
Having 16 cells in a row would be more messy from a wiring standpoint (wires from opposite ends, longer runs), plus it seems like it would be more awkward to move if I did ever need to. So two parallel rows of 8 cells seems better suited. However, Is there any concern with the one bus bar that links the two rows together being longer than the rest?

View attachment 88390

2) Bus bars.
The bus bars that were provided with the cells are totally wimpy. Max current draw by the inverter would be just under 200A, and this should be split between the two battery packs. Realistically, I won't be pulling near that for any sustained period (for one thing, the batteries would run down awfully fast), but I want to design for worst case scenario. So worst case, if one pack was offline, and I started pulling 200A from one pack, I don't want to overheat the bus bars. What size bar would I be looking at? 1/8" x 3/4"? Or should I go up to 1" wide?

3) Bus bar material.
Pretty clear I would use copper. I was assuming tinned copper (can get from onlinemetals.com). But I have seen people use untinned copper bus bars. Seems like that would be an issue, but is it a non-issue if using noalox? Is that why some have not used tinned copper?

I have never liked that setup as it puts the + and the - ends of the battery too close for my comfort too easy to drop a piece of metal to short the battery and batteries do not have fuzes built-in.
 

SparkyJJO

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Linking the two rows is no different than linking any other cell in the pack. That's from an amperage standpoint. The length of the bus bar between the two rows is likely going to be different than all the other bus bars. YMMV, check the actual dimensions.

Raw copper against aluminum terminals would lead to galvanic corrosion. A layer of conductive anti-corrosion paste would help. Tinned copper would also help. You could make the bus bars out of aluminum. However, aluminum isn't as good of a conductor as copper. The aluminum would need about twice the cross section of copper to handle the same amperage. I have aluminum bar stock that, if I ever get around to it, I'll use to replace the bus bars that came with my cells.

I recommend going with 1" wide flat bar. The reason is that it presents a wider base for a cable lug to sit on if the cable was installed perpendicular to the bus bar. A 3/4" bus bar would have some of the cable lug hanging over the edge.

I know it isn't much different, my concern was the different length - I wouldn't think it would make a difference, but then, I see all these things about equal length wires between things and how it affects cell balance, I didn't want to make something weird happen. Thanks for the input on the width of the bar, I'll go with tinned 1" wide bar.


I have never liked that setup as it puts the + and the - ends of the battery too close for my comfort too easy to drop a piece of metal to short the battery and batteries do not have fuzes built-in.

Valid point. I could easily put an insulator between the cell rows to prevent a short. The final product would also have a lid to prevent stuff from falling in.
 

houseofancients

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Linking the two rows is no different than linking any other cell in the pack. That's from an amperage standpoint. The length of the bus bar between the two rows is likely going to be different than all the other bus bars. YMMV, check the actual dimensions.

Raw copper against aluminum terminals would lead to galvanic corrosion. A layer of conductive anti-corrosion paste would help. Tinned copper would also help. You could make the bus bars out of aluminum. However, aluminum isn't as good of a conductor as copper. The aluminum would need to be about twice the cross section of copper to handle the same amperage. I have aluminum bar stock that, if I ever get around to it, I'll use to replace the bus bars that came with my cells.

I recommend going with 1" wide flat bar. The reason is that it presents a wider base for a cable lug to sit on if the cable was installed perpendicular to the bus bar. A 3/4" bus bar would have some of the cable lug hanging over the edge.
which is why i use 6062 aluminium for my bus bars and no-ox.
it needs to be a bit thicker, but will do just fine
 

SparkyJJO

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It looks like I can get aluminum that is 2x as thick for almost half the cost of the copper. Hm...
 

joanna_lannie

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It looks like I can get aluminum that is 2x as thick for almost half the cost of the copper. Hm...
For maximum performance, use copper busbars, but if you don't have special needs, brass or aluminum are also good, as you said, you can save money.
 

SparkyJJO

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I know copper is the best, typically, but since the cell terminals are already aluminum, introducing copper does introduce the opportunity for corrosion. Yes, that can be relatively easily mitigated, but it is still a factor. Then throw in that copper costs a huge bundle, if a 1/4 inch thick aluminum bus bar can handle 200A without issue (no excessive heat etc) then 1) it brings costs down and 2) removes a mixed metal situation. According to a quick internet search, 1/4" x 1" can do 300A DC on THIS CHART - I just don't know at what temperature rise. But again, I'm not going to be pulling 200A continuous from one back for any length of time, so as long as it is rated for a worst case scenario, then under normal usage it shouldn't get warm at all.

I automatically shy away from aluminum by default, partly because of the whole oxidation issue. Yes, I have noalox but it is always in the back of my mind "what if I didn't apply it fast enough, or get the contact point clean enough first?" But, I'm kinda stuck with it on the cell terminals, so...
 
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houseofancients

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I know copper is the best, typically, but since the cell terminals are already aluminum, introducing copper does introduce the opportunity for corrosion. Yes, that can be relatively easily mitigated, but it is still a factor. Then throw in that copper costs a huge bundle, if a 1/4 inch thick aluminum bus bar can handle 200A without issue (no excessive heat etc) then 1) it brings costs down and 2) removes a mixed metal situation. According to a quick internet search, 1/4" x 1" can do 300A DC on THIS CHART - I just don't know at what temperature rise. But again, I'm not going to be pulling 200A continuous from one back for any length of time, so as long as it is rated for a worst case scenario, then under normal usage it shouldn't get warm at all.

I automatically shy away from aluminum by default, partly because of the whole oxidation issue. Yes, I have noalox but it is always in the back of my mind "what if I didn't apply it fast enough, or get the contact point clean enough first?" But, I'm kinda stuck with it on the cell terminals, so...
andy at the off grid garage uses aluminium exclusively.
 

SparkyJJO

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I don't see him using noalox - any idea why not?

I just discovered I can get 96 inches of 1" x 1/4" 6063 aluminum from Home Depot shipped to my door for $27 + tax. I can get 144 inches for $24.50 from Midwest Steel, but shipping is a very high $30 for some reason. Doing a little digging it seems that 6063 aluminum may edge out 6061 on conductivity.
 
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houseofancients

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I don't see him using noalox - any idea why not?

I just discovered I can get 96 inches of 1" x 1/4" 6063 aluminum from Home Depot shipped to my door for $27 + tax. I can get 144 inches for $24.50 from Midwest Steel, but shipping is a very high $30 for some reason. Doing a little digging it seems that 6063 aluminum may edge out 6061 on conductivity.
he is in later video's , as with everything , time is a great teacher

 

HRTKD

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I don't see him using noalox - any idea why not?

I just discovered I can get 96 inches of 1" x 1/4" 6063 aluminum from Home Depot shipped to my door for $27 + tax. I can get 144 inches for $24.50 from Midwest Steel, but shipping is a very high $30 for some reason. Doing a little digging it seems that 6063 aluminum may edge out 6061 on conductivity.

Aluminum to aluminum contact would not have the galvanic corrosion like copper to aluminum would. However, a bus bar to terminal connection isn't air tight. A light layer of conductive anti-corrosion paste would help in that case.

Those prices for aluminum are really cheap!

For @joanna_lannie, this is the chart I often refer to for conductivity.
1648132584686.png
 

SparkyJJO

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I ordered the $27 bar from HD. I just now remembered DUH, I have two banks, I need more than that :rolleyes: So I'm ordering a second one. Yay for free shipping so it didn't cost me any extra after that.

I've considered adding a separate bolt/screw for the balance leads, vs using the m6 ring terminals directly. Then it seems like extra work for what seems to be no gain. Any suggestions either way?
 

HRTKD

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My plan for the aluminum bus bars is to drill and tap a new hole for attaching the balance lead. That way the balance lead ring terminal could be whatever size I wanted and it didn't go on the same bolt/stud/whatever that held the bus bar to the cell terminal.
 

SparkyJJO

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Looks like I lucked out. Those bars from Home Depot are now out of stock, can't be ordered. Will they get more? Maybe, but at what price... Either way, both bars shipped, one is supposed to be here today, and the other April 5 (not sure why that one is so late).

I'm still kicking the separate connection for the balance leads idea around. It would require additional hardware that I don't have - I have a tap but I'm pretty sure it is way too big for this application (used to recut threads for the U joint hold-down bolts on a rear differential years ago).
 

Steve_S

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A few things to ponder...
Busbar resistance does add up and makes a difference during balancing (not readily seen).
Below are common busbars sent by suppliers and what their resistance is from edge to edge.
* The 100mm longer busbar is that which is commonly used for the "bridge" between rows.
* BMS Sense leads should always be on the (+) post if not attached directly to busbar (screwed to the middle of the bar) (note 1)
! Edges, ridges & burs can & do cause problems, the contact surface MUST be perfectly smooth and the Torque should be between 4-5 PSI.
(Note:1) Usually, M4 Screws are tapped into the middle of busbars, Self-Tapping drill bits for this are available and cheap too.

Supplied BusBar Resistance Test.jpg
 
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