Two lithium, connected to bus bar

[MalibuDave42]

Hoping to get some insight from the experts... Just bought 2 280ah lithium to replace by 4 6v 2s2p lead acid. Everyone is talking about equal lengths for red and equal for black to their respective bus bars. Instead of an "interim bus bar" then run from the interim to the main bus bar. Can I run a equal reds from each battery to the main bus bar (red arrow) AND equal blacks to the "to battery" connection my my Victron Smart Shunt (black arrow)?

I plan to use 200a MRBF on each battery. Do I need a 250T before OR will the 200a BMS and 200a MRBF be safe coverage?

 

[robbob2112]

Equal length means equal round trip paths. So b1 can have a 2ft red and 1ft black and b2 can have a 1ft red and a 2ft black. So in your case total round-trip of the wires and if they have the same number of connections along the way so much the better.

Assuming you bms has a max current of 200amps discharge then you would put a 250a MRBF on thepost mount. Prevents nuisance fails and still protects the wire. If you wires from battery to bus bar are more than 12" best to put MRBF on both ends of the wire in case there is a short in the middle.
Del city is my current goto for MRBF, there are many fakes on amazon so best to avoid them for this.

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The wire from the inverter to the bus bar is where the class T fuse goes. It should be 125% of the max inverter draw.

Try not to stack lugs on each other, it can cause problems. Better to have another bus bar.

Put a thin coat of no-ox-id special on all contact surfaces...I.e. the lugs, the mrbf holder, etc.

The breaker style you are using for the MPPT to the bus bar is well know for being faked. The fakes are notorious for melty/firey failures. If you use that make sure it is bussman or other real brands.

Better to use a midnite solar breaker or din mount breaker in a small box

 

[HRTKD]

This was version 2 of my wiring from the two 280Ah 12v batteries to the shunt. Version 3 used a wider bus bar so that it covered the entire connecting surface of the shunt. The cool part of this approach is that if I had added two more batteries I would have attached them on the bottom of the copper bus bar and the balance of all four batteries would have been almost perfect.



I used the same bus bar connection method going into a Class T fuse holder on the positive side. Yes, I had only one fuse for both batteries. Not quite the way it should be done though. If there had been a version 4, I would have gone with a Class T fuse for each battery.