For two inverters run dual cables or buss bar?

[JayeTH]

Hey everyone. Getting ready to order wiring for setting up solar system for small cabin. Think i am going 6 206 amp hour batteries which will be powering two 24v 3000W inverters. I belive that means they will each pull about 125 AMPs at 24V.

So that gets to my questions. For the run from the battery bank to the inverter, if if the run is just under 9 feet from the batter bank to the inverter, can I run just one set of cables and use a bus bar on each side of the run to hook up the two? Or would it be required to run 2 sets one for each. I ran the wire calculator and it says that for up to 12 feet, 2 AWG can handle the 125A. I am thinking i need to run two sets since there are 2 inverters each at 125A? (Dashed wires)

Also, in the diagram, is that the correct way to do series/parallel to get the 24V and even pull/charge evenly across the entire bank?


Thanks in advance....anything else I should consider?

 

[FilterGuy]

If at all possible I would find a way to reduce the distance between the batteries and the inverters. 9ft is a long run for 24V systems.

Big question: Why not go with a 48V system? It would need two more batteries, but it would cut the currents in half. (I really don't like to have currents as high as this system could draw)

Assuming you can't shorten the distance and/or go to 48V, either method can be made to work if they are properly fused and have the correct wire size.

When calculating the current for an inverter, this is what I do. (I will assume the efficiency of the inverters is 90%)

1) Each 3000W of inverter will draw up to 3000W/.9W = 3333.W from the batteries.
2) When the LiFePO4 batteries are nearly empty the voltage will be ~24V therefore the current will be 3333W/24=139A. This is the worst-case continuous draw from the inverter. Presumably, the average load will be less.

If you run two sets of wires,
Each set will carry 139A and each set should be fused at the battery. The fuse should be 1.25 x 139 = 174A. You could use a 175A fuse and wire for 175A. Since class T fuses are fast blow, I would be tempted to use a 200A fuse and wire for 200A. If the run is 9', that means there is an 18ft round trip. Marine-grade 2/0 wire rated for 105deg should be OK for this and the voltage drop will be less than 3%)

If you run a single set of wires,
The wires will carry up to 2 x 139A = 278A and the wires should be fused at the battery. The fuse should be at least 25% greater than the current so they will be 1.25 x 278 = 347A (That is a LOT of Current). You will want a 350A Class T fuse and the wires must be rated to carry the full 350A. (Since class T fuses are fast blow, I would be tempted to use a 375A fuse and wire for 375A.) You will need to look up wire size and voltage drop for this.

 

[JayeTH]

Thanks... the reason for 24V is that the inverters have already been purchased. They batteries had planned to be about 6 feet closer, but had to change plans in the build. I only have two "temp" batteries so could maybe move the initial test setup to there till I get all the batteries. and then also get a new inverter. I think the shortest I could get with where all 6 batteries will fit is about 7 feet as it has to run under a floor section which is 6 foot wide That would only give me 6 inches on each side for making connections.

I like the idea of going to 48V and that may be the long range solution. I would have other uses for the current inverters after the upgrade.