Need to Size in-line Fuse for my Bus Solar Power System

[TedH]

I am preparing to install a 1500watt solar array (6, 250watt panels) to power my 24volt, 2.4Kw Lifepo4 battery system. I am using the AIMS 60amp SCC (SCC60AMPPT) and the 3000watt AIMS Inverter.

I need to establish the size(s) and quantity of inline fuses to purchase for my system. Please advise if you have recommendations on the in-line fuses to purchase.

Is it as simple as getting the fuse sized for the SCC rating (ie. 60amp)?

NOTE: I started researching and noted that 100amp in-line fuses are intended for systems with 2500watt inverters or smaller. Is 100amp in-line fuse appropriate?

Also, how many fuses do I need to put in my system other than between the SCC and battery? Add between battery and inverter? Between solar array and SCC? Just put on the (+) wire? Both (+) and (-)?

The six, 250watt panels will be setup in two serial strings of three panels connected in parallel (3 panels per parallel string).

Specs for each panel:
maximum power 270w
Open-circuit Voltage 44.4
voltage at Pmax 35.5
Short-Circuit Current 8.25amps
Current at Pmax 7.6amps
max System Voltage 600
Fuse Rating 15amps

I found this whitepaper on the Renogy site. Is it correct guidance? https://www.renogy.com/blog/how-to-fuse-your-solar-system/

 

[Dzl]

Generally speaking, the primary purpose of a fuse is to protect the wire. Generally it should be sized greater than the maximum normal current of the circuit, and less than the current carrying capacity of the wire.

A general rule of thumb often used is max current x 1.25 = fuse size (round up). However, if your device manufacturer gives specific recommendations on fusing (they often do) this would supersede that rule of thumb and should be followed. There are also situations where that may not be the optimal way to size a fuse.

This video is well worth a watch and this thread is well worth a read.

As to your specific questions:
1. For the SCC, a fuse or breaker > 60A should fit the bill. Its possible/likely the SCC manual will make a recommendation. You may also choose to put a circuit breaker or switch between your PV array and SCC to make disconnecting the power source (PV array) easier.
2. For a 3000W inverter a 100A fuse is too small. Consult your inverter manual for a recommendation, if no recommendation is given, 175-250A seems like the right ballpark. Bearing in mind the wire has to be sized larger than the fuse.
3. Regarding other fuses, every circuit should have circuit protection as close to the start as possible. And fuses should be sized to protect the smallest wire in the circuit. For a simple mobile system, usually you will have at least three fuses or breakers (1) main battery fuse and/or inverter fuse (2) solar charge controller fuse/breaker (3) DC main fuse/breaker. Then you will have fuses/breakers for each individual AC and DC branch circuit (this is easily accomplished on the DC side with a fuse block and on the AC side (if necessary) with an AC panel or breaker box)