DIY busbars, pros and cons (noob warning)

[Messier11]

Hi guys, I see that copper connection bars at 4 meters are pretty cheap. I can get 4m at 30x10mm rated for 800 As for like 250$.

Is there any downside in making your own bus bars from a bar like that and even replacing some of the cabling to the inverter with them? Just cutting them with an angle grinder and using a Pilar drill machine. Are the ones you get designed to be battery busbar polished in anyway?

Another thing I was wondering about is, if connection is so important, why are straight holes made in busbars and not a threaded hole? At least with a little thicker busbar (especially if it’s 10mm) the difference in the connection area between a threaded bolt going through a slightly too big hole in the busbar vs a screwed into a threaded hole through the busbar wouldn’t be insignificant. Or what is your thought on that?

I am also having a bit of a hard time estimating the impact of increased resistance. Resistance is proportional to length, right. But a bigger busbar — decreases — resistance right? Saw on some YT how someone got a thicker busbar and said something like, “oh the bigger busbars will have more resistance but I think it’s irrelevant” (OGG). But the opposite is through right, a thicker busbar should reduce resistance unless I am misunderstanding something (perfectly possible)?

Lastly, copper should be fairly easy to weld with gas. A welded connection shouldn’t be any worse from a connectivity POV right? I am thinking of running a copper plate right to the inverter form the battery.

Lastly 2, I’ve also been wondering if it’s possible to paint the copper bar with some kind of rubber coating/dielectric coating to make it more secure. Do anyone of you guys have experience using coatings on busbars/copper bars?

 

[TEV]

1. replacing some of the cabling to the inverter with them?

2. it’s possible to paint the copper bar with some kind of rubber coating/dielectric coating to make it more secure.

1. I see a problem if the two devices that you're connecting are not mechanically secured to each other, and vibrating/moving and putting strain on the connections points.

2. Why not just use heat shrink tubing?

 

[Messier11]

1. I see a problem if the two devices that you're connecting are not mechanically secured to each other, and vibrating/moving and putting strain on the connections points.

2. Why not just use heat shrink tubing?

Thanks, on 2, yeah that must be much better.

 

[HRTKD]

There isn't a whole lot of welding of copper going on. I found just a few videos a few weeks back on welding copper. But I was looking at TIG only. Filler rod is just a standard "rod" of wire pulled out of a Romex cable.

I am drilling the smallest hole possible in my copper bus bars and then using a suitably sized ring terminal to fit. So far, the smallest hole is ~1/4" (really something like 17/64, I believe). The counter argument to small holes/fasteners is that the larger fastener allows for more torque which could ensure a better connection.

I started a thread on making custom bus bars:

Custom Bus Bars From Copper Flat Bar

The first iteration of my system used all 2/0 cabling between the big components such as between the battery and the shunt and fuse. I'm in the process of rearranging my system to make way for an inverter/charger upgrade. In doing so, I decided to ditch the 2/0 cable where I could and use...

diysolarforum.com

 

[Messier11]

There isn't a whole lot of welding of copper going on. I found just a few videos a few weeks back on welding copper. But I was looking at TIG only. Filler rod is just a standard "rod" of wire pulled out of a Romex cable.

I am drilling the smallest hole possible in my copper bus bars and then using a suitably sized ring terminal to fit. So far, the smallest hole is ~1/4" (really something like 17/64, I believe). The counter argument to small holes/fasteners is that the larger fastener allows for more torque which could ensure a better connection.

I started a thread on making custom bus bars:

Custom Bus Bars From Copper Flat Bar

The first iteration of my system used all 2/0 cabling between the big components such as between the battery and the shunt and fuse. I'm in the process of rearranging my system to make way for an inverter/charger upgrade. In doing so, I decided to ditch the 2/0 cable where I could and use...

diysolarforum.com

Thanks!!!

My nephew is a welder so I can piggy-back on him. I know that we weld copper pipes from district heating a lot in Sweden since the water when pressured even can go north of 100 c. Don’t take my word for it, but with the right equipment I think it’s pretty easy. The melating temperature for iron is 50% higher than for copper, hence it’s more like soldering after pre-heating with like a gas warmer than traditional welding.

 

[toms]

Don’t thread the hole in the bar, the bolt needs to turn in the bar independently to the cell thread to get a clamping force.

Heatshrink over a busbar is a waste of time in my opinion - unless you also cover the terminals. I just cover the entire battery with perspex.

I’ve had no trouble with homemade copper busbars, i polished / cleaned / no-alox coated the terminal to busbar surface.

 

[TEV]

Heatshrink over a busbar is a waste of time in my opinion - unless you also cover the terminals. I just cover the entire battery with perspex.

" ... and even replacing some of the cabling to the inverter with them....."

 

[Messier11]

Don’t thread the hole in the bar, the bolt needs to turn in the bar independently to the cell thread to get a clamping force.

Heatshrink over a busbar is a waste of time in my opinion - unless you also cover the terminals. I just cover the entire battery with perspex.

I’ve had no trouble with homemade copper busbars, i polished / cleaned / no-alox coated the terminal to busbar surface.

There is definitely an enhanced risk that you don’t get enough clamping force if there is a threaded hole in the busbars — but it isn’t a must. At least not if you have some leeway regarding how hard the bolt is screwed into the hole of the cell. Right?

 

[HRTKD]

Copper is a bit more than twice as hard as aluminum. However, I would not choose to tap threads into copper and instead would simply use a bolt and nut with an appropriate method to ensure the nut does not come loose (lock washer, serrated nut, thread locker, etc).

 

[timselectric]

Current flows from the terminal to the lug or buss bar, through the surface mating point. Not through the bolt. The greater the surface contact the better the connection. Smallest hole possible to allow hardware strong enough to accomplish a solid connection.

 

[Hedges]

Don’t thread the hole in the bar, the bolt needs to turn in the bar independently to the cell thread to get a clamping force.

There is definitely an enhanced risk that you don’t get enough clamping force if there is a threaded hole in the busbars — but it isn’t a must. At least not if you have some leeway regarding how hard the bolt is screwed into the hole of the cell. Right?

That's assuming OP is referring to a busbar between threaded cells (e.g. LiFePO4 battery)
But this is posted under "Wire/Connectors/Junction Boxes" and I took him to mean a busbar connecting battery, inverter, scc. etc.

As a general purpose busbar, threaded could work.
I bought a busbar from an eBay vendor, who had drilled a bar and attached insulated standoffs. His bolt spacing wasn't ideal for my cable lugs, and holes weren't the diameter I wanted, so I made modifications. I could have built from scratch.

What I did was put bolt through a drilled hole, and connected cables top and bottom. I had one string of batteries connected to middle hole, and four inverters connected top & bottom to two bolts, one on either side.

Current flows from the terminal to the lug or buss bar, through the surface mating point. Not through the bolt. The greater the surface contact the better the connection. Smallest hole possible to allow hardware strong enough to accomplish a solid connection.

I am of the belief that contact only occurs and current flows only at a number of tiny spots actually pressed together, and nothing is flat enough to actually make contact over the whole surface. I've found articles on bolted busbars describing this. Specified torques are relatively low and result in 1000 lbs of force or so.

While we might think of making contact patch as large as cross section of a conductor with sufficient ampacity, I don't think that is so important. Copper can carry much higher current density; it is just a heating issue. Heat can escape contact in 3 dimensions, vs. just 2 dimensions for a long conductor.

I think what is most important is for the connection to be torqued properly, and for nothing to rotate the connection later which would cause it to loosen.


Welding copper would depend on quality of field construction. I don't see the need for most configurations, just straight, bent, or cut bars. If welded, I think that should be done in the shop and tested under high current (margin above the application) and tested for heating and voltage drop.

 

[timselectric]

Heat, is the enemy of electrical connections.

 

[Zil]

When "cold welding" ie; crimping lugs to copper wire works so very well, why do a procedure that is difficult, expensive and maybe not as good?

 

[timselectric]

Buss bar utilizes less failure points. And carries current more efficiently. Great for short distances and tight working space. Flexible buss bars, takes it to the next level.

 

[noenegdod]

There is definitely an enhanced risk that you don’t get enough clamping force if there is a threaded hole in the busbars — but it isn’t a must. At least not if you have some leeway regarding how hard the bolt is screwed into the hole of the cell. Right?

No. You have a threaded hole and a threaded busbar, you can screw the bolt or threaded rod into the busbar and into the hole in the terminal but the only way to get the busbar closer to the terminal is to turn the busbar in relation to the terminal. Go ahead and waste your time trying it but it does not work.

 

[HRTKD]

No. You have a threaded hole and a threaded busbar, you can screw the bolt or threaded rod into the busbar and into the hole in the terminal but the only way to get the busbar closer to the terminal is to turn the busbar in relation to the terminal. Go ahead and waste your time trying it but it does not work.

And don't hit the other terminal on the cell with the bus bar as you're rotating it. That could be interesting. LOL!

 

[Messier11]

No. You have a threaded hole and a threaded busbar, you can screw the bolt or threaded rod into the busbar and into the hole in the terminal but the only way to get the busbar closer to the terminal is to turn the busbar in relation to the terminal. Go ahead and waste your time trying it but it does not work.

As I am learning more I’ve seen how people thighten these things with meters and so forth, if that is the precision level it won’t work (or at least take a lot of tinkering to get there).

But if you can adjust the bolt screwed into the cell half a millimeter either way, and there is no precise limit how hard to screw it on, it’s not really even hard to get it right and thighly against the terminal.

Metal is flexible, the threads of both the bolt and holes can move slightly. 1mm alone is 360’ on an M6 (unless I am mistaken). The threads alone easily flex at least 15’ (1/24 of 1mm).

BUT, with that said, I am not saying that it’s a good idea. Just that it’s perhaps not quite as bad of an idea as you are suggesting.

And if you can raise the bolt +\- 0.5mm without it having an impact, it’s not even an issue because that gives you a flexibility of 360’. But it could still just be to over complicate things.

 

[Zil]

You are right there. It is not a good idea to have threaded holes in the buss bar. Beside the fact they could never be tightened properly.

 

[noenegdod]

BUT, with that said, I am not saying that it’s a good idea. Just that it’s perhaps not quite as bad of an idea as you are suggesting.

It is an idea that may somehow work in your mind but anyone with a practical understanding knows without question that it is not a solution. I am not saying you are stupid. Just the idea. It is a horrible, unworkable idea and absolutely no one should follow the suggestion. Go try it so you can gain the practical understanding and try to save the next messier11 from wasting theirs or others time.

 

[Messier11]

You are right there. It is not a good idea to have threaded holes in the buss bar. Beside the fact they could never be tightened properly.

It is an idea that may somehow work in your mind but anyone with a practical understanding knows without question that it is not a solution. I am not saying you are stupid. Just the idea. It is a horrible, unworkable idea and absolutely no one should follow the suggestion. Go try it so you can gain the practical understanding and try to save the next messier11 from wasting theirs or others time.

I am a total noob regarding electronics but not mechanics and working with metal, basically lived in a garage from when I was 14 to 20. I have worked on cars, boats and snowmobiles all my life. I think that the problem is that you don’t quite understand how metallics work if you think it would be totally impossible.

Unnecessary work requiring some tinkering? Sure I buy that (I don’t really know any specifics about how the connectivity works, what impact it would have). But take my word for it, very far from impossible to get them fastened in the right direction.

Like these threads you tap into a bar, a copper bar on top of everything which is very soft, if you over thighten it to get to the right position, unscrew it, and then screw it on again the threads will be rearranged and require much less torque to get back to the right position. It’s metal, it’s soft. If you can make microscopic adjustment to the bolt, you are there. You can just massage it. If it’s 180’ wrong the first time, turn it up side right and it’s exactly right instead. Let’s say it shall be screwed on with 30nm, and it takes 60 to get right, it’s copper threads, screw it off, and back on again and you are maybe at 45nm, over thighten it a bit more, screw off and on again and voila you get it right at perhaps 28nm.

BUT, I will take your word for that it’s not worth the hassle.