DIY Bus Bars from copper bar

[GnrlPatton]

I read through this thread: https://diysolarforum.com/threads/custom-bus-bars-from-copper-flat-bar.33832/
But my situation is a little different. I'm going to be building my pack in a 3p4s configuration (I have 12x 304aH cells and am configuring it for 12v). It will be going in my boat, once I build out a case for it of plywood and cement board. The cells I got don't have enough bus bars to connect them in the configuration I'm planning on, which is this:



So, I'm looking at building them myself. I was considering building them from lengths of cable and crimping lugs on, but I'm not sure if I have enough post to do that, plus attach the BMS leads. So I was considering buying flat copper bar, cutting it to length for each of the bars pictured (5 total) and then drilling out for the posts. Reading through the post mentioned above, I'll have to figure a way to get them drilled accurately, which I can do with my drill press I think.

I am planning on building into the case a way to compress the cells so they don't move, but I'm wondering what the thoughts from this group would be on having the solid bars connecting cells? Would having them in a boat, with potential movement, risk the posts with movement (they are welded posts, with about 3/8" available thread)? Am I better off just building the cable based bus bars so there's flexibility, and then trying to find thin enough lugs to be able to work with the available thread?

Thanks for any input,
Kevin

 

[BretS]

I used 1/4" copper bar for mine, and it worked great. Little different configuration than yours, but same idea.

 

[Zil]

You should be fine. You do want the cells to be restrained to prevent movement. ("compressed").
onelinemetals.com has many sizes of 110 copper bar. I use 1/8 thick x 1 inch wide. I tin plate with "Tinners Paste" and a torch.
I am lucky to have a friend with a Tool and Die Shop and I have access to real drill press equipment.

 

[Rocketman]

I also used online metals.com. I got 1/4” x1” tin plated copper bar stock. (I have longer studs and wanted a thicker bar. Here are a couple of pictures from my build.

Good luck

 

[chrisski]

IMO 304 ah cells are too big for a cable connection, especially 3P. THat really depends on your power output on these cells. That thicker wire is just too hard to work within a tiny area, and when I-have worked in a small area, I’m left with a cable that looks like two lugs with a tiny wire between them, and it ends up not flexible at all.

May be good to take a look at the contact area on the 304 ah cells. I have the newer 280 ah Eve cells and the contact area between the stud and the busbar is tiny. I would not want to oversize the drilled holes because of this as pictured in post #4.

 

[captainrivet]

How many amps do you draw in total?
Big inverters and eg electric galley?
The 1/4“ tinned copper bars are good for 300A continuous. I you are running a 3kw inverter plus rest of your boat you are above that.
I doubled them up as I am pulling 500A from 5,9kw inverter, so suggest to better get 20x10 or 25x8 tinned Cooper bars right away.
In a compression jig that’s fine. Drill the holes with 7mm driller for the m6 studs, this gives enough wiggle room for extensions of the cells.
Drilling copper is pita, predrill with a 3mm and take your time. The above busbars have too big holes because they were not drilled properly, only slightly oversize 6,5 or max 7mm holes. You have to really work precise here as the 304 cells have a small contact area too and you need every bit of it.

 

[captainrivet]

I used 1/4" copper bar for mine, and it worked great. Little different configuration than yours, but same idea.


View attachment 87115

These studs are by far too short for the busbars you used. Also sinking in the nuts into the busbar is contraproducrive.
Let me guess you glued in the studs with loctide and later figured out you need thicker busbars…
Also on the rear cells there should be 3 busbars connecting all 3 cells in parallel and not only one, you pull all current over one bar while rest of bank has 3 connections/bars.

 

[Kruncher]

There are some clever cats in this world.

I find these pages to be some of the best use of my free time. Haha.

 

[WindWizard]

I read through this thread: https://diysolarforum.com/threads/custom-bus-bars-from-copper-flat-bar.33832/
But my situation is a little different. I'm going to be building my pack in a 3p4s configuration (I have 12x 304aH cells and am configuring it for 12v). It will be going in my boat, once I build out a case for it of plywood and cement board. The cells I got don't have enough bus bars to connect them in the configuration I'm planning on, which is this:

View attachment 87092

So, I'm looking at building them myself. I was considering building them from lengths of cable and crimping lugs on, but I'm not sure if I have enough post to do that, plus attach the BMS leads. So I was considering buying flat copper bar, cutting it to length for each of the bars pictured (5 total) and then drilling out for the posts. Reading through the post mentioned above, I'll have to figure a way to get them drilled accurately, which I can do with my drill press I think.

I am planning on building into the case a way to compress the cells so they don't move, but I'm wondering what the thoughts from this group would be on having the solid bars connecting cells? Would having them in a boat, with potential movement, risk the posts with movement (they are welded posts, with about 3/8" available thread)? Am I better off just building the cable based bus bars so there's flexibility, and then trying to find thin enough lugs to be able to work with the available thread?

Thanks for any input,
Kevin

I used 1/2 inch copper L pipe which worked wonderful for me. It is very easy to cut with a pipe cutter. It works well at currents of 100 amps. I tried the cable with lugs and it just did not work with the current.

Procedure: Cut the pipe to the proper length. Flatten pipe with a hammer or press. Drill holes in it. Smooth it out with a drill and wire brush so it is shinny. Plate it with a nickel solution. Making the nickel solution is easy and cheap and very quick to plate the copper.

The good thing about it is you can purchase the pipe at any hardware store. The piece of nickel for the plating solution you can purchase online.

It works absolutely wonderful.

 

[GnrlPatton]

Thanks everyone for the replies! It turns out that online metals is local to me (Seattle area), so I was able to get 1/8" x 1" copper bar in the lengths that I needed, so I went ahead and purchased them. I will get the holes drilled out and then work on the nickel plating. That will be interesting with ~17" bars, but we'll see how it goes.

I appreciate all of your inputs!
Kevin

 

[BretS]

These studs are by far too short for the busbars you used. Also sinking in the nuts into the busbar is contraproducrive.
Let me guess you glued in the studs with loctide and later figured out you need thicker busbars…
Also on the rear cells there should be 3 busbars connecting all 3 cells in parallel and not only one, you pull all current over one bar while rest of bank has 3 connections/bars.

The studs are welded in, so no, I didn't "loctide" them in... and since the contact point for conducting is between the bottom of the bar and the terminal, the slight counterbore is not a problem - the nut just holds the busbar down. I sized it so one bar can carry way more than my maximum current, so one bar works fine... My cells are staying perfectly balanced after a year of use, and nothing got even remotely warm during my capacity test pulling high amps for 6.5 hours straight... so I must not be doing everything wrong as you seem to imply...

 

[BretS]

IMO 304 ah cells are too big for a cable connection, especially 3P. THat really depends on your power output on these cells. That thicker wire is just too hard to work within a tiny area, and when I-have worked in a small area, I’m left with a cable that looks like two lugs with a tiny wire between them, and it ends up not flexible at all.

May be good to take a look at the contact area on the 304 ah cells. I have the newer 280 ah Eve cells and the contact area between the stud and the busbar is tiny. I would not want to oversize the drilled holes because of this as pictured in post #4.

You may want to see if Michael Caro on here is still selling the soft washers to increase the contact area. I got some from him and they work great. Top terminal in the pic has it on.

 

[sailingharry]

I realize this is a fairly old thread. But it is very close to my question, and the best I can find on the forum. Rather than starting a new, nearly identical thread, I'll post here.

I'm preparing to do a 3P4S build of 304Ah Eve with the new 2xM6 studs. Bus bars in general, and especially flexible, for these terminals are hard to find, expensive, and not available in configurations for larger paralleling configurations.

Like OP, this is going on a sailboat. I'll be building the pack in a tight box with modest compression, so hopefully no motion anywhere. Most of my connections will involve 6 cells, either with a long bar (6 terminals in a line) or with a short/wide bar (3 terminals down each side). Of course, each terminal is 2 screws, so double the number of holes.

I'll use copper, plated with lead-free solder. Copper will be sized appropriately for the loads (400A fuse on the bank, actual loads rarely over 300A), using the 30C column here https://www.copper.org/applications/electrical/busbar/bus_table1.html (so 1/8x1.5 or 3/16X1 for the long ones, and the wide ones are a complete non issue).

Has anyone had any negative outcome from using solid bus bars? I understand the "theory" about solid bars putting undue stress on the terminals, but what about "in practice?"

 

[Rocketman]

I used 1/4” x 1” tin plated copper from online metals.

1/4" x 1" Copper Full Round Edge 110-H02 Tinned Full Round Edge | Online Metals

Order 0.25" x 1" Copper Full Round Edge 110-H02 Tinned Full Round Edge stock today on our website. Buy online with fast shipping direct to your door.

www.onlinemetals.com

I have eight 272ah cells in 2p4s setup, so my bars span between 2 and 4 cells. It is in my MotorHome. I have not had any issues with my battery.

This is my writeup I did about 3 years ago when setting it all up. (Yep lots of chit-chat in there but a few good pictures too on the second page).

Batrium Watchmon Install

Tonight I finished my battery capacity test on the Fortune 25ah batteries. Success!!! I charged the battery up to 14.4v (3.6v each. Then I turned on anything I could. I had a small 150w 12v inverter - plugged a computer into it. Had a 12v fan and a 12v LED light - with all that stuff I was...

diysolarforum.com

Edit: I just realized one of my photos is above in this thread. The comments about my holes being slightly oversized are true - and that copper is not easy to work with. But this battery has worked very well for me 24/7 over the last 3 years. My typical large load is a Victron 12/3000 inverter running the convention microwave.

 

[RCinFLA]

It is almost impossible for a DIY'er to get truly matched cells. Matching is more than just capacity matching. Very important to have similar overpotential voltage versus cell current. Ohmic series resistance needs to be matched.

There will be significantly different load current sharing between parallel strapped cells unless they are very closely matched in overpotential voltage versus cell current and similar ohmic resistance.

Slight ambient temperature differences between cells will change their overpotential voltage vs current, further degrading their load current sharing. At high total discharge current, the cell taking more of the load sharing current will generate more internal heating further reducing its overpotential voltage vs current causing that cell to take more of the total load current, making it even hotter, ....... positive feedback loop to cell damage.

Most BMS balancers trying to balance a 900 AH cell is an impossible effort.

----------------

Do not use bare copper bus bars on cell aluminum terminals. Copper core bus bars should have a nickel barrier plating to prevent copper from pitting corrosion of aluminum cell terminal surface.

 

[chrisski]

Has anyone had any negative outcome from using solid bus bars? I understand the "theory" about solid bars putting undue stress on the terminals, but what about "in practice?"

Solid busbars have worked fine for me on an RV build, but I'd be hesitant to use them on a boat build. Much more three axis movement with a boa based off what I've experienced in Boston Whalers and rubber boats.

I have solid busbars on an RV build, and its been two and a half years with 30 days of boondocking a year, and a few dozen miles down some rough roads.

If the batteries are properly compressed, then that will minimize the movement for the length of the batteries. The length most people do, the other two axis, the up and side are rarely done. The side axis can be done with a properly sized battery box, but the vertical axis is a bit harder.

Surprisingly, I've never seen a post in her saying "My solid busbars sheered a terminal off on my mobile installation."

 

[kromc5]

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Busbars I have made purchased from them.

 

[sailingharry]

kromc5,

Nice work! A question. You have some pics showing complete systems using the single stud style terminals, and the start of a system using the twin hole style. I can get my cells in either style -- do you have any thoughts on the differences? I note that you only used 1 hole of the twin style.

Also, in the complete system, where you have 4 cells in parallel then series connected to the next 4, you not only connected both sets in parallel, but you series connected each pair of cells (rather than 1 or 2 jumpers to the next set of cells). I'm thinking that solution (but with one or 2 jumpers) as it has more flexibility, or a single plate (say 3" wide by 8" long) with all the holes drilled in it. More rigid (a down side) but much cleaner/simpler.

 

[sailingharry]

Surprisingly, I've never seen a post in her saying "My solid busbars sheered a terminal off on my mobile installation."

This is my suspicion as well. It may be one of those things we realize is theoretically possible, and then make designing it out a "at all costs" kind of thing -- even though it never actually happens.

I'm not terribly worried about them getting out of line vertically. Newton mostly takes care of it. And with nominal axial compression, getting them to move vertically would be nearly impossible.

 

[sailingharry]

It is almost impossible for a DIY'er to get truly matched cells. Matching is more than just capacity matching. Very important to have similar overpotential voltage versus cell current. Ohmic series resistance needs to be matched.

There will be significantly different load current sharing between parallel strapped cells unless they are very closely matched in overpotential voltage versus cell current and similar ohmic resistance.

Slight ambient temperature differences between cells will change their overpotential voltage vs current, further degrading their load current sharing. At high total discharge current, the cell taking more of the load sharing current will generate more internal heating further reducing its overpotential voltage vs current causing that cell to take more of the total load current, making it even hotter, ....... positive feedback loop to cell damage.

Most BMS balancers trying to balance a 900 AH cell is an impossible effort.

----------------

Do not use bare copper bus bars on cell aluminum terminals. Copper core bus bars should have a nickel barrier plating to prevent copper from pitting corrosion of aluminum cell terminal surface.

I think your thoughts are theoretically correct, and in a high-C use, maybe significant. In my case, my load on 3P 300A cells will be 95% 5 to 30A (or .1C if one cell picked up ALL the load), max normal load about 100A for under 20 minutes, and theortical max load of about 200A (toaster AND coffee!) for even less. I do have a potential infrequent use-case in the future, where an air conditioner (not currently present) might draw 50A on a 30% duty cycle overnight. I think that the tail chasing issues, and large cell imbalance, are likely to be minimal. And for most of the time, the essentially non-existent current will allow each parallel set to rebalance.