Which fuse type

[zoidberg]

....to protect batteries?

I have examples, below, of two types - a Cube fuse ( 300A ) and a Megafuse ( 300A ) from 12 Volt Planet.

I have a pair of 12V/66Ah batteries, in parallel, on one side under the berth, and a single 12V/115Ah on the other side. which may later be doubled.
There's also a 12V/50Ah Start battery nearby.

Which style of fuse/holder is preferable, please, and why? Which polarity/cable should they be fitted to - Positive or Negative?

 

[Gwylan]

....to protect batteries?

I have examples, below, of two types - a Cube fuse ( 300A ) and a Megafuse ( 300A ) from 12 Volt Planet.

I have a pair of 12V/66Ah batteries, in parallel, on one side under the berth, and a single 12V/115Ah on the other side. which may later be doubled.
There's also a 12V/50Ah Start battery nearby.

Which style of fuse/holder is preferable, please, and why? Which polarity/cable should they be fitted to - Positive or Negative?

Hang on, they are just getting their anoraks on.

Anyway, received wisdom is that fuses protect the cable rather than anything else. So a fuse sufficient to protect the safe capacity of the cable would be in order.

 

[Boathook]

Always fit to the positive and as to which type I cant say. The red band on the post clamp one indicates positive and the posts are slightly different sizes though I cant remember which is bigger.

 

[VicS]

....to protect batteries?

I have examples, below, of two types - a Cube fuse ( 300A ) and a Megafuse ( 300A ) from 12 Volt Planet.




I have a pair of 12V/66Ah batteries, in parallel, on one side under the berth, and a single 12V/115Ah on the other side. which may later be doubled.
There's also a 12V/50Ah Start battery nearby.

Which style of fuse/holder is preferable, please, and why? Which polarity/cable should they be fitted to - Positive or Negative?

If you fit cube fuses ITYWF that you will need one on each battery in multiple battery banks. The mega fuse is probably therefore more convenient in this case.. The compact nature of cube fuses makes them more convenient otherwise. but it makes sense to use the same type throughout. Same rating too if possible/ appropriate to minimize the number of spares needed
Iso 10133 does not require fuses in cranking motor circuits

Fit the fuses in the positive conductors throughout the installation. 12 volt planet only list cube fuse assemblies to fit the positive post

The safe current carrying capacity of the cables supplied by the fuses should be greater than the fuse rating

 

[pvb]

I like MegaFuses and, as has been pointed out, you only need one to protect a number of batteries in parallel (on my last boat I had 6 domestic batteries in parallel with one MegaFuse).

It doesn't matter whether you fuse the positive or the negative, but it's best to choose one and stick to it, to avoid confusion. Most people choose to fuse the positive cable.

 

[PaulRainbow]

If you fit cube fuses ITYWF that you will need one on each battery in multiple battery banks.

That's not the case, unless some of the batteries were in a different location, you're protecting the cables, so you only need to fit a fuse in the one that goes to the isolator switch.

 

[PaulRainbow]

I like MegaFuses and, as has been pointed out, you only need one to protect a number of batteries in parallel (on my last boat I had 6 domestic batteries in parallel with one MegaFuse).

You still only need one cube fuse.

It doesn't matter whether you fuse the positive or the negative, but it's best to choose one and stick to it, to avoid confusion. Most people choose to fuse the positive cable.

Sorry, but i have to disagree with you there Pete. It's next to pointless to fuse the negative battery cable, what's it going to short to ? The positive cable might short on the engine.

 

[matthewriches]

I'd fit the MEGA fuse as those cube fuses in my opinion are a pain in the arse. They cause clutter on top of the batteries among other things.

I use ANL or MEGA fuses as a general rule. Always circuit breakers on commercial boats and the more discerning customers.

 

[PaulRainbow]

....to protect batteries?

No, to protect the cables.

I have examples, below, of two types - a Cube fuse ( 300A ) and a Megafuse ( 300A ) from 12 Volt Planet.

I have a pair of 12V/66Ah batteries, in parallel, on one side under the berth, and a single 12V/115Ah on the other side. which may later be doubled.
There's also a 12V/50Ah Start battery nearby.

In this installation, you would fuse the engine battery and each domestic bank. No need to individually fuse the pair of batteries in parallel, just a single fuse for the pair.

Which style of fuse/holder is preferable, please, and why?

Please yourself, it technically makes no difference. The cube fuses are compact and simple to fit, the megafuse needs an extra cable making up to go from the fuse to the battery and needs securing.

Which polarity/cable should they be fitted to - Positive or Negative?

Battery fuses go in the positive cables.

Finally, unless you have 50mm, or greater, battery cables, 300a fuses are too big. 35mm cables are only 240a.

 

[pvb]

You still only need one cube fuse.

That rather depends on how you want to wire the parallel connections. If you're happy to tuck them under the clamp bolts, fine. But not the optimum solution.

Sorry, but i have to disagree with you there Pete. It's next to pointless to fuse the negative battery cable, what's it going to short to ? The positive cable might short on the engine.

It makes no difference - if there's a short, the same current will run in the negative cable as in the positive cable. The fuse will still blow.

 

[VicS]

Sorry, but i have to disagree with you there Pete. It's next to pointless to fuse the negative battery cable, what's it going to short to ? The positive cable might short on the engine.

But the current has to flow back to the negative terminal of the battery. If that's where the fuse is it will blow!

 

[PaulRainbow]

That rather depends on how you want to wire the parallel connections. If you're happy to tuck them under the clamp bolts, fine. But not the optimum solution.

You're right, i've only used them on batteries that have had studs and posts, so the parallel cables go on the studs, the fuses on the post.

 

[pvb]

You're right, i've only used them on batteries that have had studs and posts, so the parallel cables go on the studs, the fuses on the post.

I much prefer batteries with studs, seems a neater and more sensible way of arranging connections.

 

[matthewriches]

Yup, the clamps are another point to get loose or corrode although they've done clamps since the dawn of time so I guess they're not that bad. The Victron batteries I have are just fitted with tabs, as are a lot of the Lifeline stuff I fit to bigger boats. Either tabs or studs as much nicer.

The last battery clamp I fitted was to a forklift about 4 months ago.

I much prefer batteries with studs, seems a neater and more sensible way of arranging connections.

 

[pvb]

Yup, the clamps are another point to get loose or corrode although they've done clamps since the dawn of time so I guess they're not that bad.

They've done 1-2-Both switches since the dawn of time too....

 

[matthewriches]

[ohgod]They're not that bad if you know how to use them or have a limited budget or can't pull ur ass into the 21st Century.[/ohgod]

They've done 1-2-Both switches since the dawn of time too....

 

[PetiteFleur]

Interesting and I've always fitted fuses on the positive - so why does my solar panel instructions specifically state that the supplied fuse MUST be on the negative?

 

[alan_d]

But the current has to flow back to the negative terminal of the battery. If that's where the fuse is it will blow!

Exactly - I'm surprised people need to be reminded of that. I have a 1-2-Both switch on the positive side (I know, I know ...), so the only way I could protect the wiring with a single fuse close to the batteries was to put it in the negative lead, and I am quite happy with that.

 

[VicS]

Exactly - I'm surprised people need to be reminded of that. I have a 1-2-Both switch on the positive side (I know, I know ...), so the only way I could protect the wiring with a single fuse close to the batteries was to put it in the negative lead, and I am quite happy with that.

Id use 2 fuses one in each battery positive to selector switch connection
BUT If the leads from the battery positive terminals to the selector switch are short enough ( see ISO 10133) you could put just one fuse in the connection to the common terminal of the switch.

However you do it as soon as you branch off with a lighter cable to say the domestic panel you will need a lower rated fuse to maintain protection of that cable

 

[zoidberg]

That's all helpful, thanks.

May I have a 'suppository' question?

It emerges I have some good new RED 50mm/sq tinned cable for the engine start task, which will now be fused at 300A. Would I be right in thinking that I should have 500mm/sq in BLACK, rather than 25mm/sq. as I have elsewhere?