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OffGridForGood: What is the maximum current you expect your battery bank to supply? What is the length of the individual 1AWG cables? It would be good to apply a fairly large load for 15 minutes, measure the individual battery currents and post those values here. Then disconnect the load and...

Are all these batteries LiFePo4 chemistry? What is the internal resistance of the 100 Ah batteries? What is the internal resistance of the cells making up the DIY 280 Ah batteries; these are made up of 16 cells I assume. The ideal situation would be to have the 280 Ah batteries deliver 2.8...

You have 4 100ah cells in parallel so you could discharge as much as 800 amps and still be within the max average discharge rate for the individual cells! As I mentioned one needs to watch out for overheating the busbars. You have the right idea about where to connect the BMS leads. As far as...

Here's how you could implement the half-way connection from post #4: The orange connections would be made by short cables. It would probably work best if the busbars were all one piece with 4 holes connecting the 4 terminals of one 4P string. Drilling a fifth hole would give the place to...

If you stack the two busbars you'll have a cross sectional area of 111 mm^2, which will have a resistance of .16 microohms/mm. It looks like the distance between terminals will be 36 mm, so your resistance between terminals will be about 5.8 microohms. The clamping resistance will probably be...

I'm not the only EE on the forum. Why don't you post your questions in the General Discussion forum and then everyone can benefit from the question/answer dialog resulting?

Have a look at posts #36, #37, #38, and #39. No matter how beefy the busbars, the clamping resistance remains a factor. Would your beefy busbars be copper or aluminum? What is the manufacturer's spec for the IR of your cells?

Post #4 in this long thread shows the best way to achieve (theoretical) perfect balance when busbars are being used with a parallel string of 4 batteries.. You just drill a couple of holes at the halfway point in the appropriate busbars and make the load connections there.

The links labeled "3R" must have 3 times the resistance of the links labeled "R". Stacking 3 busbars will not multiply the resistance of that connection by 3; rather, the resistance of the 3 stacked busbars will be divided by 3. To do it as I described, you would have to stack 3 busbars...

This post: https://diysolarforum.com/threads/calculation-of-parallel-string-battery-currents.37937/page-3#post-488325 discusses what can be done to improve a 5 battery parallel string. I can't answer your questions about where to get bus bars, but there are many posts on these topics. Do a...

For the "Posts" configuration, yes, the goal is to have the same cable resistance from each battery to the load points; also you need the batteries to be nominally identical. But for the diagonal connection of 4 batteries in parallel, as in this image, the cable resistance from each battery...

A couple of interesting articles about measuring DCIR and ACIR by a Keysight engineer: https://www.electronicdesign.com/technologies/test-measurement/article/21128843/keysight-technologies-measuring-dcir-of-lithiumion-cells...

So, TommyinMiami, have you decided what hookup you're going to use?

OK. I have analyzed the 3 battery parallel string in another thread: https://diysolarforum.com/threads/calculation-of-parallel-string-battery-currents.37937/post-481671 To analyze your proposed connection of 4 batteries, I'll start with the 3 battery parallel string configuration. I assume...

What is the manufacturer's specification for the internal resistance of the batteries? The link cables between the batteries look like 4/0 cable, but the cables running off to your load don't look that big; are they also 4/0?

If each 4 battery series string is considered to be a single 48 volt battery, then it can be wired as I described here: https://diysolarforum.com/threads/calculation-of-parallel-string-battery-currents.37937/post-487633 All you would have to do to achieve (theoretically) perfect balance is to...

I've been asked by @chrisski and @MisterSandals to show the details of the circuit analysis math being used in another thread https://diysolarforum.com/threads/calculation-of-parallel-string-battery-currents.37937/ The method I've used is familiar to EE's as nodal analysis, formulated using...

The very first paragraph in my post #1 says: "Readers should understand that the results I'm going to post are theoretical values obtained with mathematical circuit analysis. In the real world things will be different since battery IR is quite variable due to temperature, age, SOC, etc...

Finally, here are some results for a parallel string of 6 batteries. I probably won't go beyond this number of batteries. I'm using a value of 1 milliohm for the battery IR, and .025 milliohm for the link resistances which I think is more representative of what one gets with heavy busbars...

I'm going to deal with this in another thread. There are some additional factors I haven't been addressing in this thread.

Are all the batteries the same, or do you have a group of 3 of one kind and another group of 2 of a different kind?

My calculations in this thread have shown that just where the load connection is made to the busbars can have an effect on balance, but if the busbars are very thick the effect will be quite small. I suppose that there might be a particular connection of load to your busbars, with which you...

I've done some calculations on a 5 battery parallel string and here are my results. I'm using a value of 1 milliohm for the battery IR, and .1 milliohm for the link resistances which I think is more representative of what one gets with busbars rather than cable links. The load current is 100...

Could you indicate on my drawing where the load is connected? Is it connected in the middle or at one of the ends of the busbar?

Your diagram shows only one wire connecting to the red busbar where I've shown a blue dot. Surely you have 4 wires connected to 4 studs on the busbar I've shown as 4 big black dots; is that correct? Could you also show where your load cable is connected to the red busbar?

I haven't found a perfect balance connection for 5 or more batteries in parallel, but the method does give improvements for those cases. I'll post some of my findings about those higher number strings before too long.

Have a look at post #26 (also see post #4). The right hand part of the image shows 4 batteries connected to a common busbar with equal length cables. Whether or not it gives a balanced charge/discharge depends on how the load is connected to the busbars. If the load is connected as shown by...

Have a look here: https://diysolarforum.com/threads/calculation-of-parallel-string-battery-currents.37937/post-487633

I've done some further research and I found another way to achieve perfect balance for parallel battery strings of 3 and 4 batteries. In post #14 I showed a method to achieve perfect balance that is most practical in a setup with busbars because the method requires making the load connection...

Have you measured the currents of the individual batteries under load? It's possible to work the problem backwards and calculate what the battery parameters such as IR must be to give the measured currents.

That's better than 4/0 gauge cable! A 72mm link of that would have a resistance of .001 milliohm; that's 1 microohm! In such a case I suspect that the clamping resistance will dominate the overall link resistance. If I set the link resistance to .081 milliohms battery IR to .50 milliohms and...

I have to use actual resistance values to make calculations, so if I attribute .06 milliohms to the clamping resistance, doubling because there are 2 of them, that's .12 milliohms. Add .05 milliohms for the bar resistance, I get .17 milliohms for the total link resistance. If the battery...

What would be the typical IR for the batteries, and the resistance of the busbars between two adjacent batteries?

Here's a document put out by Hioki about their BT4560: https://www.hioki.com/download/32951 It talks about Cole-Cole plots and shows an example of one on page 2 of the document. The red line which is the Cole-Cole plot crosses the horizontal axis on the left at 1 kHz and that point corresponds...

Perhaps you're asking about sensitivity to a failure of all the battery IR's to track. Let me run an example. Set the battery IR's to 1 milliohm, typical for a somewhat high IR of modern LFP batteries, set the link resistance to 1 milliohm, higher than what a good busbar setup would give you...