Adding Terminal Fuses to Boat Batteries

[evantwheeler]

I am finishing some electrical upgrades on my boat before selling it. Added a new group 27 primary battery and keeping the group 24 as a starting/secondary backup. Previously, there was no battery switch or fuse on the single battery cable going to the starter. I'm looking at putting one each of these Blue Sea fuses on the positive battery terminal of each battery:

https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

What is the recommended fuse size? 200A sufficient for 6.2 MPI starting duties?

I am getting wildly different opinions reading other internet posts. I have 1Ga welding wire to the new Perko switch on the positve side, 1Ga from perko to the starter, and 2Ga wire on from each battery to a common ground.

 

[Nanu/Nanu]

I am finishing some electrical upgrades on my boat before selling it. Added a new group 27 primary battery and keeping the group 24 as a starting/secondary backup. Previously, there was no battery switch or fuse on the single battery cable going to the starter. I'm looking at putting one each of these Blue Sea fuses on the positive battery terminal of each battery:

https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

What is the recommended fuse size? 200A sufficient for 6.2 MPI starting duties?

I am getting wildly different opinions reading other internet posts. I have 1Ga welding wire to the new Perko switch on the positve side, 1Ga from perko to the starter, and 2Ga wire on from each battery to a common ground.

Ive got an older 454 and mine was attached at the starter im not 100% sure of the size i think may 90amps. The other one i have is on the trim pump. Wiring it directly to the battery youd have to have it pretty big for sure because youre fusing for all your loads. If you got an amp meter i suppose you could clamp your cables while starting and while running to see what it reads and fuse accordingly. Just be sure to do like a normal routine start blower on stereo. i would check with every possible thing on as well. Thats my best suggestion. I haven't read much into these but a circuit breaker that can be reset may be a better option. Fuses usually cant be reset. Just thinking if im out on the water and pop/blow a fuse now you possibly have to do a hardwire connection losing fuse protection. Sorry thats not really any good solid advice but may give you something to think about.

 

[rivermobster]

I am finishing some electrical upgrades on my boat before selling it. Added a new group 27 primary battery and keeping the group 24 as a starting/secondary backup. Previously, there was no battery switch or fuse on the single battery cable going to the starter. I'm looking at putting one each of these Blue Sea fuses on the positive battery terminal of each battery:

https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

What is the recommended fuse size? 200A sufficient for 6.2 MPI starting duties?

I am getting wildly different opinions reading other internet posts. I have 1Ga welding wire to the new Perko switch on the positve side, 1Ga from perko to the starter, and 2Ga wire on from each battery to a common ground.

I've never seen a fuse put between the battery and the starter.

What is the reason you want to do this?

 

[NicPaus]

I thought there was a fuse on the starter? On my last boat merc 454 mpi. It had a fuse on the starter.

 

[rivermobster]

I thought there was a fuse on the starter? On my last boat merc 454 mpi. It had a fuse on the starter.

The fuse, or fuse links, on the starter are Between the starter terminal, and the load.

I've never seen anyone put a fuse between the starter and the battery.

I'm Really wondering why the OP feels the need to do this?

 

[evantwheeler]

The fuse, or fuse links, on the starter are Between the starter terminal, and the load.

I've never seen anyone put a fuse between the starter and the battery.

I'm Really wondering why the OP feels the need to do this?

I wasn't aware of the fuse on the starter. I did find in my research after posting this thread that there is a similar post style fuse mounted on the starter as you three have mentioned.

 

[Nanu/Nanu]

The fuse, or fuse links, on the starter are Between the starter terminal, and the load.

I've never seen anyone put a fuse between the starter and the battery.

I'm Really wondering why the OP feels the need to do this?

I wasn't really sure the reason either. The fuses he is wanting to use are usually on the device that is drawing the load. For example a the starter, the trim pump. I haven't seen where someone has total protection on the battery with a fuse (doesnt mean its ridiculous, just means i haven't seen it). I typically see 200 amp circuit breakers off the battery. I was thinking maybe he has some stereo equipment But in that case i would maybe consider a distribution block and fuse or protect the stereo circuit separately from the other circuits.

 

[evantwheeler]

I wasn't really sure the reason either. The fuses he is wanting to use are usually on the device that is drawing the load. For example a the starter, the trim pump. I haven't seen where someone has total protection on the battery with a fuse (doesnt mean its ridiculous, just means i haven't seen it). I typically see 200 amp circuit breakers off the battery. I was thinking maybe he has some stereo equipment But in that case i would maybe consider a distribution block and fuse or protect the stereo circuit separately from the other circuits.

I used these exact fuses in my last boat for my stereo system which was a completely independent system from the engine/boat (standalone and not even connected to the alternator). Was in the middle of re-wiring the batteries on my current boat and saw an opportunity for improvement/protection of the system, not knowing about the fuse at the starter.

That being said, I believe a fuse should be AT the source of energy. As it is now, there are two unprotected cables from each battery to my Perko switch, and from my switch to the starter that in theory, could burn the boat down because they are unprotected from shorting out.....Securing everything properly should keep anything like that from happening. I realize every ICE powered thing I own has an unprotected cable from the battery to the starter.....

 

[Nanu/Nanu]

I used these exact fuses in my last boat for my stereo system which was a completely independent system from the engine/boat (standalone and not even connected to the alternator). Was in the middle of re-wiring the batteries on my current boat and saw an opportunity for improvement/protection of the system, not knowing about the fuse at the starter.

That being said, I believe a fuse should be AT the source of energy. As it is now, there are two unprotected cables from each battery to my Perko switch, and from my switch to the starter that in theory, could burn the boat down because they are unprotected from shorting out.....Securing everything properly should keep anything like that from happening. I realize every ICE powered thing I own has an unprotected cable from the battery to the starter.....

I wont argue circuit protection of any kind its a great idea. I just didn't understand why and have yet to see someone use post/terminal fuse blocks on the battery. Probably is a clean install and fits well with your battery box.

Double check your starter and make sure there is a fuse there.

Post pics of your install if you don't mind. Im kinda curious to see what it looks like and what you go with.

 

[rivermobster]

I used these exact fuses in my last boat for my stereo system which was a completely independent system from the engine/boat (standalone and not even connected to the alternator). Was in the middle of re-wiring the batteries on my current boat and saw an opportunity for improvement/protection of the system, not knowing about the fuse at the starter.

That being said, I believe a fuse should be AT the source of energy. As it is now, there are two unprotected cables from each battery to my Perko switch, and from my switch to the starter that in theory, could burn the boat down because they are unprotected from shorting out.....Securing everything properly should keep anything like that from happening. I realize every ICE powered thing I own has an unprotected cable from the battery to the starter.....

I'll respond to this when I'm at a keyboard.

Meanwhile...

Bluesea has a Really good electricial circut phone app! You might want to check that out while you wait.

 

[rivermobster]

@eventwheeler

So you definitely DO NOT want a fuse in the main battery cable between the starter and the battery. Using welding cable IS a good idea, just keep it clear of ANY moving parts, and put some kind of oil proof shielding on it. Welding cable, unlike automotive cable, was not meant to be oil or fuel resistant, in most cases.

What you DO want to do, is use the starter terminal, where the main battery cable terminates, as the take off point for all of your accessories. Is it mandatory to do it this way? Not necessarily, but probably is the most convenient.

Since you are rewiring your whole boat...

You Could put a power terminal, between the battery and the starter, and make all your accessory connections from there. This would make your main fuses, however you decide to do them, much easier to access if you did ever did need to get to them. IF the boat is wired correctly, needing to get to these points, Should be extremely unlikely, but it would be nice to have an easily accessible splice point, for any future upgrades.

Now to your Perko switch situation...

Alternators are finicky things. I wouldn't expect positive results (no pun intended), from trying to charge two DIFFERENT batteries, simultaneously. Unless you have an alternator, that was designed for dual batteries? Still not a great idea, but If it was me, I would install matching batteries, and be done with it.

Fuses...

I always use fuse links, coming of of a power point (starter solenoid, battery terminal, power point, etc...). Those are just MY personal preference, and I size them accordingly. I would then run those, to a conventional fuse block, and run each individual consumer (lights, head unit, USB power source, etc...), directly to it's own individual fuse. That way if something does blow a fuse, it's very easy to isolate the problem.

Also handy are self resetting circuit breakers, instead of fuse links: https://www.windynation.com/product...K5Ww6lZ0qssgYFFRZ_VCGsnKRZZINI0AaApJZEALw_wcB

This way if you do have a major short, once diagnosed out on the water, the circuit will reset itself automatically. Of course there are pros and cons to this, but it's a decision you can make, once you have your wiring diagram laid out. Put it all on paper FIRST!!!

Now if you wanna get really tricky? And your within the products ratings, I'm going to be installing one of these deals on my boat...

https://www.bluesea.com/products/6011/m-Series_Mini_Dual_Circuit_Plus_Battery_Switch_-_Red

SI-ACR automatically combines batteries during charging, isolates batteries when discharging and when starting engines. The Dual Circuit Plus™ Battery Switch simplifies the switching of two batteries to OFF or ON while still providing battery isolation between the engine and auxiliary battery. The Combine function can be used to parallel the batteries in the event of a low engine battery.

It basically makes life a whole easier with dual batteries.

Remember this rule...

Fuses are installed to protect the wiring, not the component! Keep this in mind, and wiring things, starts to make a lot more sense.

 

[Nanu/Nanu]

@eventwheeler

So you definitely DO NOT want a fuse in the main battery cable between the starter and the battery. Using welding cable IS a good idea, just keep it clear of ANY moving parts, and put some kind of oil proof shielding on it. Welding cable, unlike automotive cable, was not meant to be oil or fuel resistant, in most cases.

What you DO want to do, is use the starter terminal, where the main battery cable terminates, as the take off point for all of your accessories. Is it mandatory to do it this way? Not necessarily, but probably is the most convenient.

Since you are rewiring your whole boat...

You Could put a power terminal, between the battery and the starter, and make all your accessory connections from there. This would make your main fuses, however you decide to do them, much easier to access if you did ever did need to get to them. IF the boat is wired correctly, needing to get to these points, Should be extremely unlikely, but it would be nice to have an easily accessible splice point, for any future upgrades.

Now to your Perko switch situation...

Alternators are finicky things. I wouldn't expect positive results (no pun intended), from trying to charge two DIFFERENT batteries, simultaneously. Unless you have an alternator, that was designed for dual batteries? Still not a great idea, but If it was me, I would install matching batteries, and be done with it.

Fuses...

I always use fuse links, coming of of a power point (starter solenoid, battery terminal, power point, etc...). Those are just MY personal preference, and I size them accordingly. I would then run those, to a conventional fuse block, and run each individual consumer (lights, head unit, USB power source, etc...), directly to it's own individual fuse. That way if something does blow a fuse, it's very easy to isolate the problem.

Also handy are self resetting circuit breakers, instead of fuse links: https://www.windynation.com/product...K5Ww6lZ0qssgYFFRZ_VCGsnKRZZINI0AaApJZEALw_wcB

This way if you do have a major short, once diagnosed out on the water, the circuit will reset itself automatically. Of course there are pros and cons to this, but it's a decision you can make, once you have your wiring diagram laid out. Put it all on paper FIRST!!!

Now if you wanna get really tricky? And your within the products ratings, I'm going to be installing one of these deals on my boat...

https://www.bluesea.com/products/6011/m-Series_Mini_Dual_Circuit_Plus_Battery_Switch_-_Red

SI-ACR automatically combines batteries during charging, isolates batteries when discharging and when starting engines. The Dual Circuit Plus™ Battery Switch simplifies the switching of two batteries to OFF or ON while still providing battery isolation between the engine and auxiliary battery. The Combine function can be used to parallel the batteries in the event of a low engine battery.

It basically makes life a whole easier with dual batteries.

Remember this rule...

Fuses are installed to protect the wiring, not the component! Keep this in mind, and wiring things, starts to make a lot more sense.

I hAve one of these switches in my boat with the ACR. I LOVE IT! Even when im charging the batteries at home the on/off switch can be off and i can be charging battery one. Once one is charged the ACR will close and charge two until its 100% then open. In the off season i put them on a maintainer. But yeah super clean setup.

 

[rivermobster]

I hAve one of these switches in my boat with the ACR. I LOVE IT! Even when im charging the batteries at home the on/off switch can be off and i can be charging battery one. Once one is charged the ACR will close and charge two until its 100% then open. In the off season i put them on a maintainer. But yeah super clean setup.

Sweet!

Looking forward to installing the one I bought.

 

[evantwheeler]

This is done.

Added group 27 as primary, kept group 24 as backup, added Perko switch which i had from previous project, new hatch ram, new hatch ram relay, new battery charging isolator.

 

[evantwheeler]

@eventwheeler

So you definitely DO NOT want a fuse in the main battery cable between the starter and the battery. Using welding cable IS a good idea, just keep it clear of ANY moving parts, and put some kind of oil proof shielding on it. Welding cable, unlike automotive cable, was not meant to be oil or fuel resistant, in most cases.

What you DO want to do, is use the starter terminal, where the main battery cable terminates, as the take off point for all of your accessories. Is it mandatory to do it this way? Not necessarily, but probably is the most convenient.

Since you are rewiring your whole boat...

You Could put a power terminal, between the battery and the starter, and make all your accessory connections from there. This would make your main fuses, however you decide to do them, much easier to access if you did ever did need to get to them. IF the boat is wired correctly, needing to get to these points, Should be extremely unlikely, but it would be nice to have an easily accessible splice point, for any future upgrades.

Now to your Perko switch situation...

Alternators are finicky things. I wouldn't expect positive results (no pun intended), from trying to charge two DIFFERENT batteries, simultaneously. Unless you have an alternator, that was designed for dual batteries? Still not a great idea, but If it was me, I would install matching batteries, and be done with it.

Fuses...

I always use fuse links, coming of of a power point (starter solenoid, battery terminal, power point, etc...). Those are just MY personal preference, and I size them accordingly. I would then run those, to a conventional fuse block, and run each individual consumer (lights, head unit, USB power source, etc...), directly to it's own individual fuse. That way if something does blow a fuse, it's very easy to isolate the problem.

Also handy are self resetting circuit breakers, instead of fuse links: https://www.windynation.com/product...K5Ww6lZ0qssgYFFRZ_VCGsnKRZZINI0AaApJZEALw_wcB

This way if you do have a major short, once diagnosed out on the water, the circuit will reset itself automatically. Of course there are pros and cons to this, but it's a decision you can make, once you have your wiring diagram laid out. Put it all on paper FIRST!!!

Now if you wanna get really tricky? And your within the products ratings, I'm going to be installing one of these deals on my boat...

https://www.bluesea.com/products/6011/m-Series_Mini_Dual_Circuit_Plus_Battery_Switch_-_Red

SI-ACR automatically combines batteries during charging, isolates batteries when discharging and when starting engines. The Dual Circuit Plus™ Battery Switch simplifies the switching of two batteries to OFF or ON while still providing battery isolation between the engine and auxiliary battery. The Combine function can be used to parallel the batteries in the event of a low engine battery.

It basically makes life a whole easier with dual batteries.

Remember this rule...

Fuses are installed to protect the wiring, not the component! Keep this in mind, and wiring things, starts to make a lot more sense.

Thanks for taking the time.

Probably didnt do everything like DCB would, but i would rather have the group 24 as backup, than not have a backup at all. I didnt need to add a 2nd battery, but figured the next guy might appreciate it. The charging isolator opens and charges backup battery when it senses 13.4v at primary battery. Maybe alternator wont like it, but i dont see how it will be an issue since the backup wont ever really see a load/draw unless its used as a backup to start. There is an onboard dual battery charger/maintainer that is hard wired to each battery. The only excuse for a dead battery will be laziness or lack of care to plug it in.

 

[rivermobster]

Thanks for taking the time.

Probably didnt do everything like DCB would, but i would rather have the group 24 as backup, than not have a backup at all. I didnt need to add a 2nd battery, but figured the next guy might appreciate it. The charging isolator opens and charges backup battery when it senses 13.4v at primary battery. Maybe alternator wont like it, but i dont see how it will be an issue since the backup wont ever really see a load/draw unless its used as a backup to start. There is an onboard dual battery charger/maintainer that is hard wired to each battery. The only excuse for a dead battery will be laziness or lack of care to plug it in.

Just an FYI...

A Properly working alternator will put out 14.2v at all times.

Yeah so?

That means Anytime the engine is running, (with the isolator you have), the alternator will always be charging both batteries.

If it's not a high put alternator, designed for dual batteries, it's going to be working real hard at all times.

Make sure the cable, coming off the alternator, is sized to handle the full amperage output of the alternator.

 

[Justfishing]

I would say that a fuse protects the wire from an over current situation. Fuse goes at beginning of source. Think of the breKer in your house. It jeeps wire from over heating.

Individual things like amps have internal fuse to prevent malfunction from starting a fire or a brief over current from damaging the amp