How to tap this?

[bluedog225]

Good morning,

I’ve got eight 48 V lithium iron phosphate 100 amp hour batteries to be wired in parallel. Sample image below.

What’s the optimum place to tap into this bank? I’d like the individual batteries to share the load as equally as possible.

They will be connected with 4/0 wire and will feed an inverter.

Taking power off each end of the bank works but I don’t think it’s optimal.

Any thoughts welcome.

Thanks

 

[pembol]

This is the resource you need:

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

From section 3.3:

 

[Shiftless]

Does anybody else think like me that option 2 would be the way to go?
I don’t think you would really need four-aught wire for the individual battery connections… just use that for carrying the load after the splice over to the inverter.

 

[bluedog225]

This is the resource you need:

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

From section 3.3:

Yes. Thanks. That’s a good resource. I have some issues with their documentation in general. And maybe the use of “length” and ”thickness” in these examples.

A couple are a little difficult to put into practice in my situation.

The third one may be the way to go. Though I’m a little hesitant to try this with 8 absent a clearer understanding.

 

[txvwnut]

It's kind of dealers choice as any internal resistance in the conductor will dictate how current is drawn from one battery to the next plus each battery may discharge a little different rate.

 

[pembol]

To me, the 2nd option is likely the easiest. You can use slightly smaller wires from battery to junction - and is you ever need to remove or isolate a single battery, it is easy. You can also use premade cables of the same length, which could save some time/money.

 

[Shiftless]

any internal resistance in the conductor will dictate how current is drawn from one battery to the next

The resistance of the wire is constant over its length. Length of wire easy to control.

 

[Shiftless]

To me, the 2nd option is likely the easiest. You can use slightly smaller wires from battery to junction - and is you ever need to remove or isolate a single battery, it is easy. You can also use premade cables of the same length, which could save some time/money.

Looks like we now have 2 votes for that option.

(Wow! … those batteries are $1000 each )

 

[bluedog225]

[edited]

I’ve just finished making all my 4/0 cables for between each battery. And under the current plan, all cables will be 4/0.

Going from the ends can work. That’s the baseline case.

If I were to midpoint tap, I guess it would be at the “X” below? That would be pretty straightforward.

I just don’t want to screw this up.

 

[bluedog225]

Looks like we now have 2 votes for that option.

(Wow! … those batteries are $1000 each )

In terms of hardware, what does the #2 junction look like? I don’t think I want bolted together lugs.

 

[bluedog225]

Unfortunately, the started at about $1900 then came down to about $1200. Then got discontinued. Good hardware and individually replaceable bolted cells. And drop in replacement BMS. But not enough people were willing to pay the premium.

Now larger batteries available cheaper. But these should run my place for a good decade or longer.

 

[Shiftless]

In terms of hardware, what does the #2 junction look like? I don’t think I want bolted together lugs.

Yeah, that’s an issue with #2. The junction is a big chunk and not easy to do in an elegant manner.

But you will end up with a battery storage array more than equivalent to 2 Tesla Powerwalls.