First build, I have questions and would like to hear any suggestions.

[timselectric]

This attached pic is what led me to believe it was for 48V. Hopefully eggo chimes in. I emailed Victron about it, depending on what they say I'm gonna go ahead and order different ones tomorrow and get them on the way.

I will let the eggo (our Victron Guru) speak to the specific Victron equipment.
That picture shows the batteries wired in series/parallel. (Not a fan)
But, does not show the 9 fuses that should be placed on the parallel jumpers.
Those are 24v balancers wired in an overlapping fashion.
As in...... the first balancer is balancing #1 and #2, with each other. The second balancer is balancing #2 and #3, with each other. And the third balancer is balancing #3 and #4, with each other.

 

[Partimewages]

I did some research a while ago. If you go to Victronenergy.com and get the manual it shows correct wiring for what ever application you need but only up to 48 volts.

 

[JWilliams]

I will let the eggo (our Victron Guru) speak to the specific Victron equipment.
That picture shows the batteries wired in series/parallel. (Not a fan)
But, does not show the 9 fuses that should be placed on the parallel jumpers.
Those are 24v balancers wired in an overlapping fashion.
As in...... the first balancer is balancing #1 and #2, with each other. The second balancer is balancing #2 and #3, with each other. And the third balancer is balancing #3 and #4, with each other.

Thanks Tim that helps. But I won't have a choice but to wire the batteries in series/parallel right? If I have (12) 12V batteries going for a 48V system?

Also Victron responded and it's not really confidence inspiring. Attached.

 

[timselectric]

But I won't have a choice but to wire the batteries in series/parallel right?

My preference would be to put 3 sets of 4 batteries in series. And then parallel their outputs.
This will require balancing on each series set.
I'm not a fan of parallel cells or batteries (pre-built series cell strings), before series connected.
I prefer to series connect cells/batteries, to get the desired voltage. (A "battery")
And then parallel the "batteries" to make a bank.

 

[Hedges]

Something I have to choose between. For one system, 8s2p vs. 2p8s.
FullRiver AGM, page 7, says it is better to cross-tie all batteries in parallel as well as series.

https://fullriverbattery.b-cdn.net/wp-content/uploads/battery-installation-manual-english.pdf

"2.7 - CROSS TYING BATTERIES IN PARALLEL PACKS In order to maintain balance in parallel battery packs, it is best to cross tie the batteries. This method of connection will maximize the performance and life of your battery system. Cross-tying batteries means connecting positive to positives and negatives to negatives of each adjacent battery in the set. See DIAGRAM 5 below for proper cross tying connections. The dotted lines represent the cross tied cables."

 

[timselectric]

Oddly enough, they left out the fusing in the diagrams.
All parallel connections need to be fused. To protect a shorted cell/battery, from the others in parallel dumping all available power into them. (Causing a possible fire)

 

[robbob2112]

Hey @sunshine_eggo - look at this -

I knew I didn't get this idea out of thin air - cross tying batteries

 

[JWilliams]

Something I have to choose between. For one system, 8s2p vs. 2p8s.
FullRiver AGM, page 7, says it is better to cross-tie all batteries in parallel as well as series.

https://fullriverbattery.b-cdn.net/wp-content/uploads/battery-installation-manual-english.pdf

"2.7 - CROSS TYING BATTERIES IN PARALLEL PACKS In order to maintain balance in parallel battery packs, it is best to cross tie the batteries. This method of connection will maximize the performance and life of your battery system. Cross-tying batteries means connecting positive to positives and negatives to negatives of each adjacent battery in the set. See DIAGRAM 5 below for proper cross tying connections. The dotted lines represent the cross tied cables."

Just when I thought I was starting to figure this out.

 

[timselectric]

There are always multiple ways to accomplish a goal.
With different advantages and sacrifices.
You just have to decide which advantages you want. And what sacrifices you can live with.

 

[JWilliams]

Oddly enough, they left out the fusing in the diagrams.
All parallel connections need to be fused. To protect a shorted cell/battery, from the others in parallel dumping all available power into them. (Causing a possible fire)

Do you have any links to a good fusing diagram for me to follow? Or what size/type inline fuses I will need for my particular bank? I also saw where I need to fuse my incoming PV power. I'm just trying to skip the googling and research and go ahead and order all this.

 

[robbob2112]

The major problem with this configuration if you need an active balancer with enough current push to keep the different batteries balanced.

 

[timselectric]

Do you have any links to a good fusing diagram for me to follow? Or what size/type inline fuses I will need for my particular bank? I also saw where I need to fuse my incoming PV power. I'm just trying to skip the googling and research and go ahead and order all this.

No link
But just fuse at the expected balance current, with a little headroom.
You are just trying to stop a current dump across the parallel connection.
For the PV , no fuses are necessary for most situations. (Depends on configuration of array)
But it's always recommended to install a maintenance disconnect. (Which can be a breaker)

 

[JWilliams]

No link
But just fuse at the expected balance current, with a little headroom.
You are just trying to stop a current dump across the parallel connection.
For the PV , no fuses are necessary for most situations. (Depends on configuration of array)
But it's always recommended to install a maintenance disconnect. (Which can be a breaker)

I'm back and forth on this fuse issue. Really the last thing I haven't bought. I keep reading conflicting information on how to choose the correct amp fuse. As @Hedges stated, these are 3000W per battery. So please forgive me if I'm completely off here I'm just assuming... But 3000W÷48V = 62.5A, then if I have 4 paralleled sets of (4 in series) 62.5×4 = 250A. So I could possibly need like a 275-300A fuse? Just 1 on the main line going to the inverter? Or am I supposed to be doing a fuse in-between each paralleled set? And will my 1/0 pure copper cable even safely handle that many amps? (Pic attached) If that is too much I can go just back down to 3 paralleled sets (187.5A).
Also, if I only need 1 on the main line my plan was to just get an inline breaker to take the place of a fuse and battery switch.

 

[JWilliams]

Here is the left off pic.

 

[timselectric]

You need a fuse on the main Positive of each battery string. Sized to protect the conductors.
Then a small fuses on each parallel balancing jumper.

 

[Hedges]

I've been thinking about my 2p8s (or 8s2p) pack.
If anything could disconnect one string (or cell), or it stops supplying current letting the other carry all, then jumpers for one string need to carry 100%.

What I wanted to do was have oversize fuse only for catastrophic shorts at the battery pack, and wires to each inverter protected against overload by breaker built into inverter.

If I'm not going to make every jumper large enough, then 8s2p with fuse or breaker per string is one option.
My batteries came with enough (~2 awg, 35mm) wires to cross-tie this bank. That's 170A at 75C in free air, 190A at 90C.

My inverters are 1x 5kW and 1x 5.75kW. I figure 2 battery strings each with its own 35mm jumpers are sufficient, but if one disconnected it would not be.
However, considering 250 Ah 6V batteries, if one cell or one string is disconnected, 250 Ah x 48V = 12000 Wh.
Discharging at 1C rate that is 1 hour to empty. (Low voltage disconnect would come late if only one cell is 100% DoD, others 50%.)
11kW inverter / 48V * 1.12 ripple factor = 256A, even higher as battery approaches 42V LVD.

That wire is going to get HOT and insulation will be damaged, but I don't think ignition temperature. And no opportunity for shorting to other wires within array.

With battery bank crosstied, 2p8s, I think even if a cell goes open circuit, I still have two parallel jumpers everywhere, so no overload of wires.

Do you have a reason to think with two batteries tied in parallel there is more risk when one cell shorts, compared to cells 2x as large?
For 2V cells, I would think probably not.
For 6V batteries, 3 cells in series, one shorted cell would mean 4V battery in parallel with 6V battery, which would proceed to cook the two other cells, causing outgassing.

 

[timselectric]

The usable current should flow through each string.
The cross tied jumpers, should only be carrying balancing current.
If a battery or cell fails, you want the connection to open. (Fuse blowing)

 

[Hedges]

I don't think failed cell will blow a fuse except (1) hard shorted cell in parallel with good cell, or (2) undersize fuses in cross connections.

If I put a small fuse in cross connect, then a weak cell could cause it to blow, and full current draw would come from the remaining cell, and its series connections. Therefore, series connections would have to be large enough for full current.

A BMS that monitors individual cell voltages (or currents) could implement protection for such issues.

Separate strings (8s2p) with two fuses is one way to avoid the problem.
Question is whether any benefit to cross-tying. Battery balancers would be an alternative.

 

[Hedges]

Here's a 4p16s LiFePO4 pack. Solidly cross-tied.

Very new to solar but started purchasing items, not sure of the final specs of the whole system.

Looking better; when I tested the 4s/5s3p paralleled, the voltage dropped significantly. The victron handles the lower voltage better than the 18kpv mppt.

diysolarforum.com

What we were seeing for early EV packs was small cells (size used in laptops), individually series fused by sheetmetal (tinplate steel?) busbar.

 

[robbob2112]

I've been thinking about my 2p8s (or 8s2p) pack.
If anything could disconnect one string (or cell), or it stops supplying current letting the other carry all, then jumpers for one string need to carry 100%.

What I wanted to do was have oversize fuse only for catastrophic shorts at the battery pack, and wires to each inverter protected against overload by breaker built into inverter.

If I'm not going to make every jumper large enough, then 8s2p with fuse or breaker per string is one option.
My batteries came with enough (~2 awg, 35mm) wires to cross-tie this bank. That's 170A at 75C in free air, 190A at 90C.

My inverters are 1x 5kW and 1x 5.75kW. I figure 2 battery strings each with its own 35mm jumpers are sufficient, but if one disconnected it would not be.
However, considering 250 Ah 6V batteries, if one cell or one string is disconnected, 250 Ah x 48V = 12000 Wh.
Discharging at 1C rate that is 1 hour to empty. (Low voltage disconnect would come late if only one cell is 100% DoD, others 50%.)
11kW inverter / 48V * 1.12 ripple factor = 256A, even higher as battery approaches 42V LVD.

That wire is going to get HOT and insulation will be damaged, but I don't think ignition temperature. And no opportunity for shorting to other wires within array.

With battery bank crosstied, 2p8s, I think even if a cell goes open circuit, I still have two parallel jumpers everywhere, so no overload of wires.

Do you have a reason to think with two batteries tied in parallel there is more risk when one cell shorts, compared to cells 2x as large?
For 2V cells, I would think probably not.
For 6V batteries, 3 cells in series, one shorted cell would mean 4V battery in parallel with 6V battery, which would proceed to cook the two other cells, causing outgassing.

My handy calculator shows your 1awg will be about 543c. Not good