Confused about fuses needed for 12v system

[CalemChiara]

Hello, I thought I’d make a post to get some help if possible.
I am new to solar and am designing a 12v system for my campervan. I plan to use the system mainly to charge my phone, iPad, juicer, and most importantly my ebike battery, which is about 1000w total, so that’s why i have a large lithium battery.

My specs so far are:
- 2 solar panels (1x160w, 1x350w), wired in parallel. About 30amps total i think.
- 40a renogy rover mppt charge controller
-1500w/3000w pure sine wave inverter
- 300ah LiFePO4 12v battery

So I am watching Will’s classic 400w 12v solar tutorial and have some questions.

In his video, he has a main fuse which is a 170amp circuit breaker, connected to his fuse block and inverter, and then he also has a bolt on 170amp fuse on his battery cord.





But in his diagram, he only has 1 main fuse, which I’m guessing is a a bolt on fuse to the battery?




So, I am trying to get my head around this. So taking this image below as an example, my questions are:
1) for the ‘main fuse’, can it be a circuit breaker like the one in the first image in the red circle? (Assuming it’s the proper size for the amperage)
2) Do I need a second fuse on the positive battery cable? Say a bolt on fuse, like the one he uses in the first image in the blue circle? And if so, why do i need 2 big fuses? And what size would this fuse need to be? I thought one was enough for the invertor, does the battery need its own fuse?
3) Last noob question haha, can i copy the setup below, but instead of using a bus bar, just put all the negative leads on the negative battery pole, and skip the negative battery cable he says to connect to the bus bar?



So yeah, that’s it really. I can’t seem to figure out why he has 2 big main fuses (one on the battery cord, and one bolted on the wood), especially when the diagram only has 1 big main fuse and 1 for the charge controller. Does it have something to do with using a lithium battery instead of agm, since they can start bigger fires and need more protection?
And I’d rather not use a bus bar, so was just wondering if that is more for convenience and managing wires when the battery might get a bit crammed.


If you read this far, thank you so much! I‘m a total noob with this stuff so thank you so so much for your time and any help you provide!

Thanks

 

[Goboatingnow]

By and large each wire directly connected to the battery terminals needs a fuse right at the battery and sized to protect the wire not the connected appliance.

Charge sources , ie anything generating power , should be fused at both ends , ie near the charge source and the battery. Again fused to protect the wire.

Every wire including things like shunt sense wires should be fused near the battery terminal.

 

[CalemChiara]

Oh cool, thanks for replying!
So just to clarify, if the positive battery wire is to be fused at the battery terminal, it would just need a fuse that can handle the wire amperage x1.25? And then the rest is the same as the diagram?

 

[grncdr]

it would just need a fuse that can handle the wire amperage x1.25?

I guess this thread is a bit old, but in case you've already installed your system, I wanted to point out that you've got the relationship backwards here. You want a fuse with a _smaller_ current rating than your wire, the idea is to have a fuse blow before your wire starts on fire.