Connecting cells

[LVLAaron]

I have 16x 100AH packs.

Connected in 4P4S config - So I'll need to connect the P strings. I was planning on using 4GA welding wire. For this short run (less than a foot) will I have any issues? The math checks out but I am curious if the hive mind that is much smarter than me has any advice to avoid unforeseen problems.

 

[FilterGuy]

I have 16x 100AH packs.

Connected in 4P4S config - So I'll need to connect the P strings. I was planning on using 4GA welding wire. For this short run (less than a foot) will I have any issues? The math checks out but I am curious if the hive mind that is much smarter than me has any advice to avoid unforeseen problems.

4P4S can dump a *lot* of current. What is the max load your system will draw from the battery bank? 4AWG is only rated for 80A (or 960W @ 12V).

 

[LVLAaron]

The charts I saw, noted that 4ga should handle something like 200amps over a short distance.

Is there a chart or calculator that we trust I can look at?

 

[Lt.Dan]

Depends on the load TBH. Some guys have used 0 gauge between packs. @cinergi comes to mind, and it created more problems than it was worth and ended up reorganizing to use copper bus bars again.

 

[FilterGuy]

The charts I saw, noted that 4ga should handle something like 200amps over a short distance.

Are you talking about 4 gauge or 4/0 gauge?

I use the Blue Seas chart.... but it is conservative compared to some others.

 

[FilterGuy]

Depends on the load TBH. Some guys have used 0 gauge between packs. @cinergi comes to mind, and it created more problems than it was worth and ended up reorganizing to use copper bus bars again.

The downside of using cable is that on each connection you have 2Crimps that must be solid, and even then they add resistance.

The upside to using cables is that they are flexible and allow a little movement of the cells relative to each other.

 

[LVLAaron]

4

 

[LVLAaron]

The downside of using cable is that on each connection you have 2Crimps that must be solid, and even then they add resistance.

The upside to using cables is that they are flexible and allow a little movement of the cells relative to each other.

Yeah. I wish I could skip the cable between strings and just use a bus bar, but the way the packs are built it's not really condusive to bolting it together that way.

 

[FilterGuy]

4

Wow! Could you provide a link to that chart? 200A seems like a *lot* for 4AWG.

 

[Lt.Dan]

There's no way 4ga is carrying 200a lol. Even 2AWG with 200*C silicon coating is like 195 amps I think.

 

[A.Justice]

I have 16x 100AH packs.

Connected in 4P4S config - So I'll need to connect the P strings. I was planning on using 4GA welding wire. For this short run (less than a foot) will I have any issues? The math checks out but I am curious if the hive mind that is much smarter than me has any advice to avoid unforeseen problems.

Why not just bolt the second set of batteries to the same bus bar? It looks like they are almost touching as-is. I almost don't see the point of using wire at all.

 

[LVLAaron]

Why not just bolt the second set of batteries to the same bus bar? It looks like they are almost touching as-is. I almost don't see the point of using wire at all.

I'd like to. The leads and terminals are pretty stiff. There's no way I can get them all connected to a central bar without really stressing existing wires more than I'm comfortable with.

 

[LVLAaron]

I think I'll find some different bus bars and arrange them like this. It will fit better in the RV this way anyway.

 

[cinergi]

Depends on the load TBH. Some guys have used 0 gauge between packs. @cinergi comes to mind, and it created more problems than it was worth and ended up reorganizing to use copper bus bars again.

Indeed. To anyone using an inverter on a battery, I'd recommend against using wires to connect cells together to form a pack. There amount of voltage fluctuation at the per-cell level was incredible and caused all kinds of problems at the BMS layer (e.g. it would start balancing when it shouldn't, think a cell is too high when it's not, etc).

 

[LVLAaron]

Indeed. To anyone using an inverter on a battery, I'd recommend against using wires to connect cells together to form a pack. There amount of voltage fluctuation at the per-cell level was incredible and caused all kinds of problems at the BMS layer (e.g. it would start balancing when it shouldn't, think a cell is too high when it's not, etc).

I noticed this with even some low amperage loads on my test bench.

I've ordered some 1/8th x 1in 110 copper bar from onlinemetals

 

[LVLAaron]

Got my copper bars in, and have a nice box built around it all. Almost done with the project.