Battery Fusing

[sailorboy1]

I have 4 house batteries in parallel. Three of them are right next to each other and the other is around 12" away which I will call Battery #1 as that is were the house positive cable connects. So the positive jumpers from batteries 2-4 are 6" long and the one from #1 to #2 is about 12-18". There is a 300A fuse installed in the cable at battery #1.

Is there suppose be a fuse installed at batteries 2, 3, 4?

[CharlieJ]

Not required.

But for belt and suspenders it wouldn’t hurt to put an MRBF on batteries 2, 3 & 4.

[sailorboy1]

But doesn't ABYC say that needs to be protection with 7" of a source?

[CharlieJ]

@sailorboy1:
The 7” requirement is for the main OCPD. And their is an exception for that requirement.

[noelex 77]

From a practical point of view the most important consideration is that the battery interconnect’s cannot create a short circuit. Battery short circuits are bad news.

This may involve steps such as securing the interconnecting wires in a way that prevents them creating short even if they become disconected. Cable ties, conduits and plastic boots around the positive and negative terminals are a significant help.

These steps are easy and cheap to install.

You can also fuse each of the batteries. This creates multiple extra points of failure. Despite this drawback it can be sensible precaution if there is still a risk of the interconnecting cables creating a short circuit despite the steps suggested in the second paragraph.

[smac999]

If they are 10’+ away I fuse jumpers. at 12” I would not have even considered it. Abd I would remove it. Because you will never know if it blows. One day you will simply lose 25% of battery and never know.

Just don’t let the pos and neg jumpers touch each other, then nothing can ever happen. Cover in split loom if touching things that could rub through.

[sailorboy1]

The more I think about it the more I think every battery needs protection. In my installation a short in any location before the main cable fuse would result in all 4 batteries discharging.

BTW the way not fusing with thinking you wouldn't know if it blew seems WAY down the worries of a battery discharging to ground and blowing up.

[smac999]

Originally Posted by sailorboy1

The more I think about it the more I think every battery needs protection. In my installation a short in any location before the main cable fuse would result in all 4 batteries discharging.

BTW the way not fusing with thinking you wouldn't know if it blew seems WAY down the worries of a battery discharging to ground and blowing up.

Just position the batteries and jumpers so they never touch each other. It’s normally not hard. Then nothing can ever happen. This is my main thought when making jumpers

Lithuim I fuse each battery

[sailorboy1]

Originally Posted by smac999

Just position the batteries and jumpers so they never touch each other. It’s normally not hard. Then nothing can ever happen. This is my main thought when making jumpers

They are and each is covered and each positive terminal is covered. But that changes nothing. Even if a jumper would suddenly break in half it couldn't ground to anything. But I bet this is a "everyone does it that way" thing, which does not make it right.

[skipperpete]

I’ve been following the threads about emerging chemistry technology batteries with interest and was surprised to hear that in the US the main positive battery cable to the starter motor on pleasure craft is fused. I’m very familiar with battery isolating switches but in my entire working career to date across a very broad range of diesel engine applications and Kw outputs I have NEVER seen a fused main cable.
Ok, put down the pitchforks, I completely understand that the huge battery loads that are increasingly common on cruising yachts need to be vigorously protected by all of the methods discussed on this forum but the possibility of losing the engine completely needs to be seriously considered. We now live in an age of electronically controlled common rail diesel engines and soon they’ll be the only option so we should be rethinking our approach to keeping em firmly connected to DC.
I’ve seen a lot of battery and electrical fires both on boats and in a variety of other installations but battery chargers and neglect have been the culprit on the fires that I’ve actually seen on yachts ....and for the others, often metal items bridging the terminals.... quite a few gas explosions ranging from blowing off the cell lids to (in my own 4wd) total destruction of the battery when the foil covered soundproofing came away from the hood and settled on the battery... while I was driving. Possibly of interest, my latest 4wd has an “explosive disconnect” on the battery +ve triggered apparently by the airbag deploy circuitry.
No machinery or engine supplier to the best of my knowledge ( Cat, Cummins , MTU, kenworth , Mack, Yanmar etc etc) fits a main cable fuse (other than maybe my airbag one)
but all have, or recommend a battery disconnect switch.
I recently read of a boat with a fuse installed in the main +ve that has run for 24,000 hrs and never blown a fuse but as I said earlier, I applaud the use of robust protection systems for the huge electrical loads that cruising yachts now routinely sail with.
Pete.

[CharlieJ]

and was surprised to hear that in the US the main positive battery cable to the starter motor on pleasure craft is fused

@skipperpete
You heard incorrectly: That is the only significant conductor that is not required to have OCPD.