Blue sea class T VDC?

[MartyByrde]

For 320A of charge current you definitely need 4/0AWG.


0.5C on a 280Ah battery is 140A and 1C would be 280A.

That's per battery in parallel. So 4 in parallel can handle 4 x 140A = 560A at 0.5C. So you will have no issue with 320A. Even 3 in parallel can handle more than 320A.

I wasn’t planning to have them in parallel. Is that the only way it would be safe?

 

[rmaddy]

I wasn’t planning to have them in parallel. Is that the only way it would be safe?

You have 4 48V batteries. They have to be in parallel. If you connect the 4 batteries in series you will have a 192V system.

The battery and bus bar arrangement I described in post #16 puts the batteries in parallel.

 

[MartyByrde]

You have 4 48V batteries. They have to be in parallel. If you connect the 4 batteries in series you will have a 192V system.

The battery and bus bar arrangement I described in post #16 puts the batteries in parallel.

Thanks for clarify, I went back and that makes sense.

 

[MartyByrde]

With 4 big batteries like that I think it makes sense to have two sets of bus bars. Wire the 4 batteries in parallel to the first pair (battery bus bars).

Wire the all-in-one and two charge controllers to the other pair (system bus bars).

Then run a big wire with the 400A Class T fuse between the two positive bus bars. I would put a battery monitor shunt on the big negative wire connecting the two negative bus bars.

Here's the fun part with the 4 batteries and the battery bus bars - you should put a smaller Class T fuse between each battery and the positive battery bus bar (so that's a total of 5 Class T fuses). Size the 4 smaller Class T fuses to match the max charge current of each battery.

Imagine the scenario where you have a full 320A of charge current. 60A will go to each battery (this assumes each battery is rated that high - you never answered that question). Now think about what happens if one battery fails at this point. Now that 320A will be split between 3 batteries. That's a bit over 100A going to each battery. That might be too much. The smaller fuses for each battery can act as a primary safety before the BMS has to kick in.

Do you think I need 4/0 for the batteries?

 

[rmaddy]

Do you think I need 4/0 for the batteries?

Not for the wires connecting each battery to the battery bus bars. Since each battery is not carrying the full 320A charge current you can use smaller wires.

Pick a max charge current you want to support. 0.5C is 140A and 1C is 280A. I would try to keep each battery's charge current on the lower end.

You could plan for a max of 80A (320A / 4) per battery or 100A (320 / 3 roughly). The latter allows 3 batteries to still charge if 1 shuts down for some reason. If you do that then use a 125A fuse on each battery and use 2AWG for each battery to easily handle the 100A.

If two batteries shut down for some reason then the remaining two won't be able to handle the full 320A of charge current. The 125A fuses will pop before the 2AWG wires go bad on those two batteries.

 

[MartyByrde]

Not for the wires connecting each battery to the battery bus bars. Since each battery is not carrying the full 320A charge current you can use smaller wires.

Pick a max charge current you want to support. 0.5C is 140A and 1C is 280A. I would try to keep each battery's charge current on the lower end.

You could plan for a max of 80A (320A / 4) per battery or 100A (320 / 3 roughly). The latter allows 3 batteries to still charge if 1 shuts down for some reason. If you do that then use a 125A fuse on each battery and use 2AWG for each battery to easily handle the 100A.

If two batteries shut down for some reason then the remaining two won't be able to handle the full 320A of charge current. The 125A fuses will pop before the 2AWG wires go bad on those two batteries.

That makes sense, thank you. I found this video as a guide for what I believe you described for the busbars at timestamp 1:50

 

[MartyByrde]

Not for the wires connecting each battery to the battery bus bars. Since each battery is not carrying the full 320A charge current you can use smaller wires.

Pick a max charge current you want to support. 0.5C is 140A and 1C is 280A. I would try to keep each battery's charge current on the lower end.

You could plan for a max of 80A (320A / 4) per battery or 100A (320 / 3 roughly). The latter allows 3 batteries to still charge if 1 shuts down for some reason. If you do that then use a 125A fuse on each battery and use 2AWG for each battery to easily handle the 100A.

If two batteries shut down for some reason then the remaining two won't be able to handle the full 320A of charge current. The 125A fuses will pop before the 2AWG wires go bad on those two batteries.

I have been ordering 5/16” lugs. Do you think I should be using 3/8”?

 

[HRTKD]

I have been ordering 5/16” lugs. Do you think I should be using 3/8”?

Buy lugs that fit the stud. Lugs with a hole that is too large for the stud probably make less surface contact.