To fuse (or not to fuse) – advice requested

[Johnrunberg]

Don't know why but I've never had an easy time with wiring. Doesn't make sense most of the time. So I'll ask a question!

Here's the stuff:
100w foldable panel (2x50w) going to a 20a MPPT controller to an Odyssey PC1750 (think it will fit later on in the Vanagon...) deep cycle battery. Off the battery will be a Blue Sea 6 position fuse panel which then will go out to an assortment of Blue Sea cig plug, USB port and Anderson PowerPole ports. 10g wiring. Not wiring to the starting battery of my Vanagon for the moment but instead installing in a spare Pelican box.

Here's what I'm thinking:

• With a short circuit current of 6.17a I'm under the impression that no fuse is needed between the panel and charge controller. If one is used it would be 10a (6.17*1.56 factor = about 9a).
• Definitely DO need a fuse between the MPPT and battery. According to the instructions a 20a MPPT needs a 20a fuse.
• Best understanding is that each power draw should be fused and OK to do so at the fuse panel. Match the fuse to the rating of the port and/or draw of the device if using the PowerPole (whichever is less).
• That SAID should I have a fuse between the battery and fuse block = to the max amp draw possible? Or is that really needed?

Gracias in advance...

 

[228B]

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It's considered "optional" to fuse PV at the controller. I did. For a disconnect as much as anything else. You may use circuit breakers too, but ones also considered switchable. I went with the far less expensive Maxi blade automotive fuse, 30A. (the green colored fuse to the left of the charge controller)
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Everything begins at the battery. The battery's positive lead should be fused within six inches of the positive terminal. I fused my battery + lead w/ a 60-amp fuse (the blue colored fuse on top of and in the middle of the battery) because my "shore" charger outputs 50 amps in the rare occasion it is used. My battery serves a camp trailer portable solar setup which powers an Engel MT-45 and a few lights. The accessory load circuit from the solar charge controller is limited to 15 amps. I went straight to a fuse block to fuse individual accessory circuits including the Engel fridge.
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I did not keep this modified sine wave inverter, but the 1/0 cable will feed the next one I install. I fused that at the battery's Positive post with a 225-amp block fuse, and it only serves the inverter.
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[AndrewP]

John-I would not feel the need to fuse that. Technically every power source should be fused at the source, but a 100 watt panel is pretty low power and unlikely to burn up any reasonable wiring even in a worse case scenario.

The battery is a different story. It can supply hundreds of amps and can easily burn down your truck, so absolutely fuse any wire connected to your battery at your battery!

 

[Joe917]

Don't know why but I've never had an easy time with wiring. Doesn't make sense most of the time. So I'll ask a question!
Match the fuse to the rating of the port and/or draw of the device ...

Fuse to protect the wire. Port rating and device draw do not matter. The fuse is there to protect the wire.
Voltage drop between the charge controller and battery will significantly affect charge times. Keep the runs as short as possible.