Fusing Your Batteries - Another Option

[Maine Sail]

I don't think many folks are aware of the Blue Seas MRBF fuses so I thought I post about them. The "Marine Rated Battery Fuse" / MRBF is a neat device. It allows you to meet the ABYC standard of having a fuse within 7" of the battery but without needing to make a short 7" battery cable and or finding a place to mount a breaker, ANL or mega type fuse. While used boats do not need to comply with the ABYC standards fusing the bank or banks just makes good common sense in many applications.

I actually fuse both my banks and my alternator. Having had the starter wire chafe through on the engine mount, on a brand new boat, within 4 months, really drove this home. Catalina had met the ABYC by encasing the cable in conduit but the conduit ended short of the starter and the cable was just too tight and close to the motor mount. Fortunately this bank was fused, and it blew. Had it not been fused it may have been a boat fire..

I have always used ANL fuses and fuse blocks but they require more install time and a jumper cable. The MRBF's are reasonably priced and fuses can be had from 30A to 300A

A single post is $16.49 at Defender and a 200 amp fuse is just $13.99. This is a very inexpensive way to protect your vessel and cheap insurance..

Features:

Interrupt rating satisfies ABYC requirements for DC Main circuit protection on large battery banks
Ignition protected—safe for installation aboard gasoline powered boats
Clear window—visual indication of blown condition
Color coded for each amperage
Meets SAE J1171 external ignition protection requirements
Rated IP66—withstands water from heavy seas

Quote Blue Seas:
"Electrical shorts are the number one cause of fires on boats. In fact, more than half of boat fires are electrical in origin. More than half of those are caused by short circuits, most in the DC circuits. If you add any circuits to your boat, make sure they are protected."

With battery fuses you want to protect the battery cable from over heating and melting in the case of a short so any fuses should be sized based on the battery cable or wiring you are protecting. If your needs for fusing are less than what the cable needs then you can always insert circuit protection at less than the cables rating. For many years I have used 200 amp ANL fuses even though the wire can safely handle 300 amps +..

A double post MRBF holder and a 150 amp MRBF:

Close up of a 300A MRBF:

Single MRBF post installed:

For more information on fuse sizing read this: Blue Seas Circuit Protection

 

[rpwillia]

Nice Idea

MS, Good post. How do we determine the best size? I have 4D's but wouldn't it depend more on my expected load? Worst case would be running the windlass, and all the electronics at the same time, I would think.

 

[duality]

could you post some pictures of dirt on your boat, i am starting to think you are not human!

mike

 

[rpwillia]

Clearly Duality was talkin to MS

My boat is not near as clean as MS's is.

 

[RAD]

So glad you posted this because as an electrician this has been on my mind given the amount of unprotected positive cable in my boat and while I'm replacing my battery's in the next couple of weeks these fuse's are now part of the project, again thanks your valuable input

 

[RAD]

Just checked these out on the Blue Sea site and what a neat little product

 

[Sumner]

That is pretty slick....I'm getting two and some fuses.

Thanks,

Sum

 

[Maine Sail]

MS, Good post. How do we determine the best size? I have 4D's but wouldn't it depend more on my expected load? Worst case would be running the windlass, and all the electronics at the same time, I would think.

It's a little complicated to explain but Blue Sea does a nice job explaining it. Here's a link to the article:

Blue Sea Circuit Protection - Fuse Sizing

 

[Ron20324]

My B323 is SUPPOSED to have those, but the dealer just threw them in the spares kit. Seems the bunk boards would have rested on the post, causing a problem of it's own. Make sure you have the overhead clearance.

 

[Hermit Scott]

MS-could you post a picture of how you have your batteries hooked together?
There are threaded studs near each battery post. I ran some aluminum rails to join each battery together. (2X125ah in parallel) I took it apart and cleaned everything and refilled the batteries with distilled water last week. The way I have it is not safe, because there is a long hot, non-fused aluminum bar in the battery compartment. Do you join your batteries with cables?
I was doing some wiring also last week and I was crimping soldering and shrink wrapping the terminals. I was wondering if you ever solder the battery cables to the battery terminal clamps?

 

[BobM]

Definitely something I want to do but....

...it is confusing as to what amp fuse to buy. Should I use the wire to the battery as a guide? or the battery itself as it would be the source of the amperage?

Bob,

Most any battery has the available current to fry even the largest battery cable therefore the fuse is generally used to protect the wire with batteries. There are some battery banks out there that can deliver 5000 amps hence the 10,000 AIC rating of the MRBF fuses which is 5000 more than the ABYC requirement. This means that you would need 10,000 amps available to create an arc and weld the fuse closed rather than having it fail open.

 

[Maine Sail]

MS-could you post a picture of how you have your batteries hooked together?
There are threaded studs near each battery post. I ran some aluminum rails to join each battery together. (2X125ah in parallel) I took it apart and cleaned everything and refilled the batteries with distilled water last week. The way I have it is not safe, because there is a long hot, non-fused aluminum bar in the battery compartment. Do you join your batteries with cables?
I was doing some wiring also last week and I was crimping soldering and shrink wrapping the terminals. I was wondering if you ever solder the battery cables to the battery terminal clamps?

I crimp only and used large battery cable like 1/0 or 2/0 between the batts. Using hot aluminum is a dangerous situation it also puts the entire load, movement load, of the batteries on the battery post. Proper Type 2 or Type 3 stranded cable is very flexible and will not transmit the full load of the weight of a battery onto the posts. I always put a slight bend in the cable to allow flexibility.

 

[DannyS]

Thanks for posting this Maine. I bought one of these fuse blocks last summer to protect a single battery I installed on our boat to run the inverter which runs the tv/dvd player (it's for the kids...I swear!) The fuse didn't fit over the terminal on the battery and I couldn't figure out how to make it work. I just assumed it was another product that my local "marine store" employees had no idea how to make function properly so now it sits in my spare parts locker. I figured I'd get back to it sooner or later, now I know what I need to make it work. Thanks again!

 

[jsalley]

I had the same problem with my starter wire chafing against the engine block that MaineSail described. Luckily I saw it before it shorted, and secured the cable with an insulated clamp away from the engine. Again, Catalina used a piece of plastic conduit to protect the cable that was too short, and didn't cover the section of cable beside the engine. Worse, there were NO fuses ANYWHERE in the battery cables - not sure if this was simply an oversight on my boat, which is an early build in the series, or a wider deficiency. I posted about it on the 309 Group Forum, and suggested that anyone with a 309 urgently check into it. I added the Blue Sea battery post fuseblocks with 250 amp fuses - it takes about 5 minutes to install them, and is really cheap and easy protection from a potential catastrophe.

 

[seadaddler]

Alternater

What's the proper size fuse for the heavy gauge wire going from the alterater to the battery bank.
Going sailing everyone have a great day
Nick

 

[Hermit Scott]

I crimp only and used large battery cable like 1/0 or 2/0 between the batts. Using hot aluminum is a dangerous situation it also puts the entire load, movement load, of the batteries on the battery post. Proper Type 2 or Type 3 stranded cable is very flexible and will not transmit the full load of the weight of a battery onto the posts. I always put a slight bend in the cable to allow flexibility.

I will change it before I take it out again. I am not sure if I have the proper crimp tool. I have an nice swage tool. But I don't know if it's for crimping wire. I use it to swage aluminum ferrels or buttons on wire rope.
The holes for swaging are labeled 2,3,4,5, and 6 for the largest hole. Is this what you use or something else?

 

[rpwillia]

Follow Up

... I added the Blue Sea battery post fuseblocks with 250 amp fuses

John, Since my 310 is similar (different engine), how did you arrive at 250 amp fuses. Off the top of my head I am thinking 125 amps, but I can be convinced otherwise.

 

[druid]

Hmmm.... while fusing the battery bank SOUNDS like a good idea, I'm not sure you're not just buying false security. A 200A fuse?? It would take a hellova short-circuit to draw over that from 12V (<0.06 Ohms), but a much higher-resistance (lower-current) short would certainly have enough energy to start a fire.

I could see maybe a 50A fuse on the house bank (provided you didn't have a big invertor), but much more than that and I don't think you're doing much good.

druid

 

[Maine Sail]

Hmmm.... while fusing the battery bank SOUNDS like a good idea, I'm not sure you're not just buying false security. A 200A fuse?? It would take a hellova short-circuit to draw over that from 12V (<0.06 Ohms), but a much higher-resistance (lower-current) short would certainly have enough energy to start a fire.

I could see maybe a 50A fuse on the house bank (provided you didn't have a big invertor), but much more than that and I don't think you're doing much good.

druid

A 250 amp ANL blew on my boat from a dead short in a 1/0 wire. The wire was fine except for where it shorted on the motor mount. False security, I avoided a boat fire that day, I think not. There is a reason there are standards in place for battery fusing.

Battery fuses are to protect the large battery cables as EVERYTHING beyond the battery cables, windlass, DC panels, inverters etc. should all have their own fuses and branch circuit fuses. Battery fuses are to protect the battery cables and they can carry a hell of a lot more than 50A...


For short circuit protection (non motor loads):

Quote ABYC E-11:
"11.12.1.5.2. Each fuse or trip-free circuit
breaker shall be rated in accordance with E-11.12.1.3
and E-11.12.1.4 and shall not exceed 150 percent of
the conductor ampacity in TABLE IV . (See FIGURE
15.)"

105C Wire From Table IV

2 ga = 210 amps + 150% allowable
1 ga = 245 amps + 150% allowable
1/0 = 285 amps + 150% allowable
2/0 = 330 amps + 150% allowable
3/0 = 385 amps + 150% allowable
4/0 = 285 amps + 150% allowable

I personally don't push it to the 150% level but that level will blow or trip a breaker. Even a 2 GA wire, when shorted, can blow a 300 amp fuse. 210 X 150% = 310 amps.

 

[druid]

If you do a DEAD short, you are correct. But if you're using 1/0 wire, chances are there is less resistance in the wire than there is in the short, so MOST of the energy in the short is at the short itself, not in the wire. THAT is where the fire will start. In fact, even a dead short with several feet of 1/0 wire may not heat the wire to "fire temp" because the battery may not be able to put out sufficient amperage.

Try this: take your 1/0 wire and get some nicely-corroded aluminum. Place the bare wires on the aluminum a few inches apart. (I'd only do this while wearing GOBS of safety equipment, and with a large bucket of cold water handy...)

My guess is the wires will be fine, the 250A fuse will not blow, but the aluminum will get VERY hot and possibly melt or even catch fire. You can try this with various other simulations of short-circuit conditions, and I'll bet unless you jam the wires themselves tightly together (which is not a likely scenario for a short cct), the fuse will not blow.

druid - ever tried welding with a 12V battery?