Any issue connecting 4AWG cable to bus like this?

[TomC4306]

Maybe just replace the Phillips screws with an appropriate hex head machine bolt with washer and lock washer.

Might make torqueing easier.

I love the hardware drawers at Home Depot and Lowe's.

 

[AlaskanNoob]

You think one battery getting less amps makes a difference in balancing?

What happens when you pull a large load? Will it matter that one battery is providing 30% more power under load?

I spent a lot of time making sure my battery cables were the exact same length. At 50% inverter load, I was within 3% output for each of my two batteries; at 10% inverter load, it changed to 8%.

I think that if you have batteries connected together in parallel, that you want the cables from each of them to the bus bar to have the same resistance so that they're both getting the same amps. The BMS can adjust, but it's best practice to ensure both are getting the same amps.

When you pull a large load, it should be split evenly among the batteries. So one battery should not be providing 30% more power under load.

I also think that modern BMS can account for these differences, so it likely won't make a difference.

In my case, with each battery individually wired into the bus bar (8 individual batteries), it wouldn't matter.

That's my understanding anyway. With zero experience, no education, and less than optimum research skills.

 

[AlaskanNoob]

Maybe just replace the Phillips screws with an appropriate hex head machine bolt with washer and lock washer.

Might make torqueing easier.

I love the hardware drawers at Home Depot and Lowe's.

I wonder what Sunshine_Eggo would think of your suggestion?

 

[sunshine_eggo]

I wonder what Sunshine_Ego would think of your suggestion?

LOL... I see what you did there. Cute.

Look up the torque spec on #8 and #10 threads.

Then look up the torque spec on the stud size for your lugs.

There's your answer.

 

[AlaskanNoob]

LOL... I see what you did there. Cute.

Look up the torque spec on #8 and #10 threads.

Then look up the torque spec on the stud size for your lugs.

There's your answer.

From what I can find after ten minutes of wading through the Internet, is that #10 fasteners (maybe that's not threads) have torque ratings as such:



And Blue Sea specs say 18 inch pounds for the #10.

As to the torque requirements for a 25-8 lug, or for the stud, I can't find anything. Haven't found it in Blue Seas documentation. I'm sure it's on the Internet somewhere but I've exhausted my fifteen minutes of trying to look through verbiage to find it.

 

[AlaskanNoob]

I don't understand why would have to do that? Not only could you use the bolts that your fuses are connected to already you can at least double up on each bolt (you flip one lug upside down and add other lug right side up). That's why those bolts are so long to begin with so that you can double and triple stack lugs on them.

So if the bus bar is toward the bottom in these photos, which one(s) of these are acceptable (I used a larger cable for the question rather than the 4AWG)?

A:


B:


C:


D:


Hopefully having some bend like in D would be okay because that lower bus bar is blocked by the upper bus bar.

 

[wheelman55]

The goal is for the lugs to lay flat against the busbar.

 

[400bird]

A, but with both wires hanging down, stacked right on top of each other.

I'd rather drill out and use larger bolts in place of some of the screws.

 

[AlaskanNoob]

A, but with both wires hanging down, stacked right on top of each other.

I'd rather drill out and use larger bolts in place of some of the screws.

Maybe it will not be so pronounced with 4AWG, but I would expect there to be a gap between the two lugs given the shape of them. They won't lay flat on top of each other I don't think, but I'll check it out tomorrow.

 

[AlaskanNoob]

The goal is for the lugs to lay flat against the busbar.

One lug will be flat against the busbar, and the other lug won't touch the busbar doing it this way. I'm guessing you mean one lug laying flat against the busbar and the other lug laying flat against that first lug? Which I think means the cables have to not be on top of each other (and best would be to do it like rhino said, with cable opposite direction).

As in picture A.

 

[400bird]

Maybe it will not be so pronounced with 4AWG, but I would expect there to be a gap between the two lugs given the shape of them. They won't lay flat on top of each other I don't think, but I'll check it out tomorrow.

Like this, but with a bus bar and bolt not pliers and a random chunk of copper.

 

[AlaskanNoob]

Like this, but with a bus bar and bolt not pliers and a random chunk of copper.

View attachment 166038

Ah, that makes sense. I bet that would work with the 4AWG nicely. Thanks!

 

[Tomthumb62]

Maybe it will not be so pronounced with 4AWG, but I would expect there to be a gap between the two lugs given the shape of them. They won't lay flat on top of each other I don't think, but I'll check it out tomorrow.View attachment 166037

You offset them. Or place the “bottom” of each lug facing the other and the “top” of the first lug on the bus bar. But doing it the second way sometimes requires you crimp your lugs such that it will work without needing to try try twist the cable.

Edit: @400bird beat me to it!

 

[400bird]

If you do double stacked lugs, just remember you're putting double the current through the bottom lug. Make sure all the connections are perfect and torqued properly.

What is your expected current from each battery at max load?

 

[AlaskanNoob]

That looks like it will work with the 4AWG. Of course I'm going to be putting bigger lugs on it here soon, but I would imagine it won't change much.

 

[AlaskanNoob]

If you do double stacked lugs, just remember you're putting double the current through the bottom lug. Make sure all the connections are perfect and torqued properly.

What is your expected current from each battery at max load?

Each battery can charge or discharge 100A. So potentially 200A going through the bottom lug.

 

[400bird]

Each battery can charge or discharge 100A. So potentially 200A going through the bottom lug.

But can your inverter pull 800 amps? I suspect you're more in the 300 amp total sort of ball park, so less than 100 amps on the bottom lug.

 

[AlaskanNoob]

But can your inverter pull 800 amps? I suspect you're more in the 300 amp total sort of ball park, so less than 100 amps on the bottom lug.

You're correct, it's 250A continuous and 520A peak power that it can pull. Thankfully, because I haven't seen any ampacity rating for the lugs but 4AWG is only about 100A so I'm guessing the lugs aren't twice that (but I have no idea).

So with 8 batteries, each should be pulling at most 31A continuous.

The MPPT can supply 200A and that will double when I put the second MPPT up. But that's 50A per battery, so that should work too.

 

[Hedges]

Can you explain this? I would think that if 200A need to travel, traveling a longer distance will allow the heat to be spread over a bigger piece of bus bar, if the big wires are attached at the far ends from each other. Battery on one end and inverter on the other. If they’re right next to each other, that heat is going to get absorbed into a much smaller piece of bus bar.

I think the idea is that the more metal it has to travel through is more resistance thus more heat.

Bingo.

Longer busbar is a zero-sum game for heating. But more voltage drop.

If you had 4 batteries and 4 inverters, worst setup would be:
Battery, Battery, Battery, Battery, Inverter, Inverter, Inverter, Inverter,

100% of current through busbar cross section.

Best setup might be:
Battery, Inverter, Battery, Inverter, Battery, Inverter, Battery, Inverter
or:
Battery, Inverter, Inverter, Battery, Battery, Inverter, Inverter, Battery,

25% of current goes through cross section

I think I'd double stack the batteries only. So one battery might get less amps due to the longer travel of the power, but since I'm wiring each battery into the bus individually and not wiring them together, I don't think it matters for balance reasons.

Instead of stacking battery cables, how about stacking one inverter with one battery cable?
[Battery/Inverter], [Battery/Inverter], [Battery/Inverter], [Battery/Inverter]

0% of current goes through cross section of busbar (except for imbalanced draw.)


My setup has one battery string and 4 inverters.
[Inverter/Inverter], Battery, [Inverter/Inverter]

Those cables are stacked one on top, one on bottom of busbar.

DIY Bus Bar

Im looking to make my own DIY Bus Bar that can pull 1000amps as buying one is expensive. Im looking to use it to connect a large battery banks. Can this be dune with supplies from hardware stores? Anyone know a good way to make on and what parts to use? The only one I can buy is this...

diysolarforum.com

Of course cable resistance dominates.

 

[AlaskanNoob]

So I was able to cut my positive cables by 18 inches, and my negative cables by 11 inches. Little shorter anyway. Will get the correct lugs on them tomorrow for the terminal studs.

Sure do appreciate all the feedback.

 

[wheelman55]

I line picture “D”. Any configuration where the lugs are flat to busbar and each other.

Depending on how flexible the wires are, you might want to do a dry fit and mark both wire and lug so when they get crimped the lugs will lay flat together against the busbar.

If you have 4 wires/lugs make sure to do a unique mark on each of the 4 sets. This could be a series of lines, a “V”, an upside down “V”, letters and marks…whatever.

This way the lugs will end up where they should be when you go to connect.

 

[wheelman55]

So I was able to cut my positive cables by 18 inches, and my negative cables by 11 inches. Little shorter anyway. Will get the correct lugs on them tomorrow for the terminal studs.

Sure do appreciate all the feedback.

NOOB. I believe that the wires should all be the same length, both positive and negative.

Did you cut them already?

 

[AlaskanNoob]

NOOB. I believe that the wires should all be the same length, both positive and negative.

Did you cut them already?

I did. But *I think* you want the batteries to have the same length positive cables, and the same length negative cables, but positive cables don't have to be the same length as the negative cables.

Of course now that I've cut them all, it would be right about time to learn that I'm wrong. That would be par for the course.

 

[Quattrohead]

Answers are given to your questions but you don't like them, sometimes reality is not convenient.

What is not clear to me is they say "smaller gauge wire" and I get that. But that isn't specific. What gauge wire? Smaller than what? If it's so clear, they should list the gauge wire that is appropriate or not.

If you cannot figure this out either mechanically or electronically, you should not be doing this project.

 

[wheelman55]

I did. But *I think* you want the batteries to have the same length positive cables, and the same length negative cables, but positive length <> negative length.

Of course now that I've cut them all, it would be right about time to learn that I'm wrong. That would be par for the course.

NOOB. Check with an expert. I’ve always been told to make both positive and negative the same length. But do check.