Fuse sizing to battery connection questions

Heyo, solar friends! I am doing a modified "The Minimalist" system from Will's website and I have a question on fuse sizing and wire gauge. I have attached a photo of what I'm planning for the system. I wanted to connect the battery directly to the charge controller because the battery has no BMS and I can set the low voltage disconnect with the charge controller. Since I'm not doing the system exactly like Will, I have some questions about fuse sizing and wire size. I am using the Victron 100/20 charge controller which has a max wire size of 10 AWG, but the Blue Sea Systems fuse box doesn't specify wire size.

2 questions:

1.What size fuse would I need to connect the charge controller to the battery?
2. What size wire and fuse would I need to connect the fuse block to the battery?

I have the questions written on the diagram below. If anyone can help, I would super appreciate it!! Much love, y'all.

Your SSC is 20A max, I think you are fine with a 25A fuse and a 10AWG Cable.

You want/need a means to disconnect the PV from the rest of the system (either before or after the charge controller, or both). You could switch out the fuse for a breaker or add a disconnect

If that is the Blue Sea 100A fuse block, the maximum fuse size should be 125A, and the wire should be rated for at least that much. You also want to consider voltage drop, If it were me I would be trying to keep Vdrop below 1% for this stretch.

Dzl said:

You want/need a means to disconnect the PV from the rest of the system (either before or after the charge controller, or both). You could switch out the fuse for a breaker or add a disconnect

If that is the Blue Sea 100A fuse block, the maximum fuse size should be 125A, and the wire should be rated for at least that much. You also want to consider voltage drop, If it were me I would be trying to keep Vdrop below 1% for this stretch.

Click to expand...

Doesn't the charge controller have a setting for the disconnect? I bought the Victron because it's supposed to be so customizable.

I've been doing a little more research on wire sizes - with the Blue Sea Fuse box, I probably would never run more than 20 amps through it at one time (at least right now. I bought it knowing that it would be useful if I upgrade at some point) - so I was thinking that I would probably run 8-10 gauge wire to it from the battery with a 60 Amp fuse on the positive cable. If this all sounds really bad, please let me know.

ValkyrieVanLife said:

Doesn't the charge controller have a setting for the disconnect? I bought the Victron because it's supposed to be so customizable.

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I'm not sure what type of built in disconnect you are talking about. Victron SCC's are very customizable, but what I'm talking about is a manual disconnect as a safety feature and for ease of maintenance. A circuit breaker or switch like this:



The Victron manual actually reccomends this, though there reccomendation isn't that clear:

Provide a means to disconnect all current-carrying conductors of a photovoltaic power
source from all other conductors in a building or other structure.

Click to expand...

I've been doing a little more research on wire sizes - with the Blue Sea Fuse box, I probably would never run more than 20 amps through it at one time (at least right now. I bought it knowing that it would be useful if I upgrade at some point) - so I was thinking that I would probably run 8-10 gauge wire to it from the battery with a 60 Amp fuse on the positive cable. If this all sounds really bad, please let me know.

Click to expand...

This is just personal preference, but if it were me, I would just size it for its rated current (100A). Its probably only a few extra dollars in wire for a system this small, and it means you won't have to remember to rewire it in the future if you want to expand or deal with nuisance trips.

So long as your wire can handle the max current you expect to draw, and the fuse will trip before the wire rating is exceeded, it should be safe.

Agree with @Dzl for long term safety - install separate devices to be able to isolate/disconnect PV input.

Also, installing equipment with cabling and over current protection that is sized on opinion of usage is a poor practice for multiple reasons. The largest reason is long term safety using the system. Abused conductors (to small for load) are a significant fire hazard. Code based installs will not allow installations that use this design criteria. I do understand that code compliance may not be a requirement, but codes help us understand the minimum requirements to achieve safety in most common situations.

See this post and thread for additional comments on cabling and OCP sizing of a system.
https://diysolarforum.com/threads/h...design-and-input-on-grounding.7238/post-82154