Battery Fuses. Terminal Fuse Block.

[thinwater]

My last boat came with a high amp (200?) fuse adjacent to the batteries. My current boat has no local fuse, but only a single group 24 battery and very low house loads; LED lighting, a few instruments, a tiller pilot (12 A) fuse), and cell phone charging). I'll need to total it up, but I serious doubt I could ever pull more than 30 amps and probably never more than 6-8 (very light boat for this tiller pilot).


I'm thinking a Terminal-mounted fuse would be fine. Any reason not? Maybe 40 amps? The cable is large enough for that.




https://www.bluesea.com/products/519...k_-_30_to_300A

[Fortytwo]

Look at ANL fuses and fuse blocks.

[Shanachie]

The rule is to fuse to the cable/wire. You want to break the fuse before the cable melts and/or catches fire.



If you've got thick battery cables, you can go to 200 or 300 amp fuses with no problem. (Look up the chart on sizing.) Installing a smaller fuse wins you no points.


If you have an inboard, you definitely want to be in the 200-300 range due to the temporary but huge surge from starting. A proper fuse has a little bit of a delay so a short surge from starting won't pop it.


A smaller fuse is OK with an outboard, especially if your battery cables are small.

[Shanachie]

Also, the terminal fuses work fine. I've used them for years.

[thinwater]

Originally Posted by Shanachie

... A smaller fuse is OK with an outboard, especially if your battery cables are small.

Pull-to-start. Which is why I didn't list starter inrush.

[thinwater]

Originally Posted by Fortytwo

Look at ANL fuses and fuse blocks.

Yes, I already know about these. I had them on my last boat. Do you have a specific point?

[Statistical]

What type of battery?

For FLA/AGM and smaller LFP then yeah terminal fuses are fine. For larger LFP installs you will want class T fuse at the battery.

As for the fuse size you can fuse lower than the cable but I wouldn't get crazy. You may draw more amps than you think or upgrade the system in the future. You can't fuse higher than the cabling supports though. If the wiring supports 230A then 200A fuse is fine and if you want to drop that down to 100A feel free but 300A is not fine (technically you could go to 250A because 230A fuses doesn't exist but I wouldn't).

[Knotical]

I installed 300A fuses similar to the one shown in OP’s picture on my 2 x Gp 31 FLA batteries.

[thinwater]

Originally Posted by Statistical

What type of battery?

For FLA/AGM and smaller LFP then yeah terminal fuses are fine. For larger LFP installs you will want class T fuse at the battery.

As for the fuse size you can fuse lower than the cable but I wouldn't get crazy. You may draw more amps than you think or upgrade the system in the future. You can't fuse higher than the cabling supports though. If the wiring supports 230A then 200A fuse is fine and if you want to drop that down to 100A feel free but 300A is not fine (technically you could go to 250A because 230A fuses doesn't exist but I wouldn't).

A single AGM. This thread is about small, simple boats.



Yes, I understand about high interrupt ratings (refinery experience).

[Wotname]

AFAIK, there is no downside (in your stated usage) in using a MRBF and plenty of upsides.

I now use them everywhere except for situations that need a high interrupt rating.