Main Fuse on Battery

Power Boats only. Please include the boat type in your question.
TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: Main Fuse on Battery

Post by TomW1 »

TomTom I'm just now looking at your drawing I notice that you have an 80amp fuze going to to motor. Get rid of that you only need the 150amp fuze at the battery for the motor. I would check your owners manual whether you need a 150 or 200amp fuze since the 150 and 200HP Yamahas are built on the same bodies and both can have a 50amp alternater. I don't know what that 80amp fuse is for.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

User avatar
APLJaK
Active Poster
Active Poster
Posts: 218
Joined: Fri Aug 21, 2009 12:39 am
Location: Okanagan Valley, BC Canada
Contact:

Re: Main Fuse on Battery

Post by APLJaK »

On my CX19/Yamaha F115 I did fuse my starter cable. I realize that I don't need too, but the idea that a dead short would have to melt a 1/0 copper cable concerns me a lot. I used a 200A Blue Sea on battery fuse (MRBF). I have 1/0 from the battery-battery switch-Distribution Terminal Block in starboard motor-well compartment. From there, the Yamaha supplied (and much lighter) cables go to the engine.

I am using two 12V Group 31 AGM 1000MCA/105Ah batteries, one for the engine and one for the house. Bad things could happen if there was ever a short and I am MUCH happier knowing that there is a fuse in the cable, even if it is a bit of a last resort. FWIW - 200A is probably way oversize for what I need on this cable for a small F115, but I have not put an ammeter on it yet. Will do so in the spring.

When I had the marine survey done, the surveyor commented that I didn't need to fuse this wire, but that he does so on his own boat as well.

TomTom
* Bateau Builder *
* Bateau Builder *
Posts: 736
Joined: Thu Nov 22, 2012 10:29 am
Location: East Africa

Re: Main Fuse on Battery

Post by TomTom »

APLJaK wrote: Wed Jan 05, 2022 7:34 pm On my CX19/Yamaha F115 I did fuse my starter cable. I realize that I don't need too, but the idea that a dead short would have to melt a 1/0 copper cable concerns me a lot. I used a 200A Blue Sea on battery fuse (MRBF). I have 1/0 from the battery-battery switch-Distribution Terminal Block in starboard motor-well compartment. From there, the Yamaha supplied (and much lighter) cables go to the engine.

I am using two 12V Group 31 AGM 1000MCA/105Ah batteries, one for the engine and one for the house. Bad things could happen if there was ever a short and I am MUCH happier knowing that there is a fuse in the cable, even if it is a bit of a last resort. FWIW - 200A is probably way oversize for what I need on this cable for a small F115, but I have not put an ammeter on it yet. Will do so in the spring.

When I had the marine survey done, the surveyor commented that I didn't need to fuse this wire, but that he does so on his own boat as well.
Thanks for this. Good to know.

Do you know how much current your starter draws? Did you go for a fuse just above that or how did you work it out?

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Main Fuse on Battery

Post by fallguy1000 »

The only reason to consider fusing a starter wire is to prevent the wire from burning in a dead short or from the starter pulling too much current.

Sizing the fuse to the wire is standard protocol.

Most rigging tubes/grommets are not large enough for a wire that matches the fuse required by starter current; so you can't follow standard protocols.

Another option to consider is a battery switch. If you can turn off the battery in a short or problem; that is also a good backup. Edited

If in doubt, use a 300 amp fuse; it should not errantly blow and would protect a catastrophic event.

I will not fuse mine, but I am able to turn off the battery.
My boat build is here -------->

viewtopic.php?f=12&t=62495

TomTom
* Bateau Builder *
* Bateau Builder *
Posts: 736
Joined: Thu Nov 22, 2012 10:29 am
Location: East Africa

Re: Main Fuse on Battery

Post by TomTom »

I have a battery cut off switch… I will stick with that then.

User avatar
APLJaK
Active Poster
Active Poster
Posts: 218
Joined: Fri Aug 21, 2009 12:39 am
Location: Okanagan Valley, BC Canada
Contact:

Re: Main Fuse on Battery

Post by APLJaK »

I agree with the battery shutoff switch being a necessity. I have my batteries amidship (LOL) so there is still a pretty long run of wire to the motor. It is also in a chase that I can't see immediately. Even if it is a remote possibility, I am still happier with both the battery shut off switch and the fuse.

There is nothing wrong with not fusing a battery cable to/from the engine and ABYC specifically states that this fuse is optional.

Below is my main bus wiring (roughly - I have made some changes, including use of larger batteries and changing the fancy Blue Sea 8690 panel for a Blue Sea Battery ON/OFF/Both Switch 5511E). Cables E & L are the cables in question. No fuse required, but not prohibited.
CX19 Main bus
CX19 Main bus

User avatar
APLJaK
Active Poster
Active Poster
Posts: 218
Joined: Fri Aug 21, 2009 12:39 am
Location: Okanagan Valley, BC Canada
Contact:

Re: Main Fuse on Battery

Post by APLJaK »

TomTom wrote: Wed Jan 05, 2022 9:52 pm

Thanks for this. Good to know.

Do you know how much current your starter draws? Did you go for a fuse just above that or how did you work it out?
No, I made an educated guess at this point and rounded up. I'm confident that 200A is way overkill but is also very much under what my main battery cables (1/0) are good for. The fuse will not blow when the starter is engaged but if for some reason the cable is compromised, the fuse will go before the cable melts or ignites. I will place an ammeter on the starter circuit in the spring. The boat is under a tarp (and a pile of snow) at the moment. We used it with the 200A fuse with no issues last season. Easy enough to carry a spare fuse just in case. FWIW, the Yamaha F115 supplied motor cables are about 1/2 the size of my battery cables. They are maybe a #4-#6. I used the Yamaha cables from a terminal block beside the motorwell to the motor as they fit the Yamaha OB grommets and terminals.

TomTom
* Bateau Builder *
* Bateau Builder *
Posts: 736
Joined: Thu Nov 22, 2012 10:29 am
Location: East Africa

Re: Main Fuse on Battery

Post by TomTom »

APLJaK wrote: Thu Jan 06, 2022 3:14 pm I agree with the battery shutoff switch being a necessity. I have my batteries amidship (LOL) so there is still a pretty long run of wire to the motor. It is also in a chase that I can't see immediately. Even if it is a remote possibility, I am still happier with both the battery shut off switch and the fuse.

There is nothing wrong with not fusing a battery cable to/from the engine and ABYC specifically states that this fuse is optional.

Below is my main bus wiring (roughly - I have made some changes, including use of larger batteries and changing the fancy Blue Sea 8690 panel for a Blue Sea Battery ON/OFF/Both Switch 5511E). Cables E & L are the cables in question. No fuse required, but not prohibited.

Boat_Battery_switch_alternate.png
Thanks for all this info. I ended up extending the existing Yamaha cables - but using them through the grommet to the engine as well.

David 9 boats
New Poster
New Poster
Posts: 4
Joined: Sat Jan 01, 2022 2:13 am
Location: Oregon

Re: Main Fuse on Battery

Post by David 9 boats »

Hello Everyone. Just to introduce myself, I have worked in the marine electric/electronics field with numerous companies around the USA for25+ years. Before that I was in air traffic control maintenance for 10 years with the Navy. Simply, this means I generally know I am talking about, so please do not beat me around the head too much. I have been retired for 14 years now, so I am behind on all the newest equipment. Basic electrical systems never change. My ABYC book is about 45 years old.
For to my two cents worth. ABYC, if memory serves, calls of for cut off switches on all batteries at a short distance from the battery. The wiring diagram shown and discussed, show an incorrect way to use a One-Two-Kill Both batteries switch. The 1-2-B switch should feed from both start and house to the engines. One for each engine. To provide backup house power for starting. House batteries are normally deep cycle types and should not mix with starting batteries in parallel. House battery should have is own On-Off switch. FYI, when plastic switch terminals loosen and/or corrode, resistance goes up, heat is generated and plastic softens (melts). The glass filled switches last longer, more $. How about riveted aluminum boats that put the battery negative to the hull like an automobile. Deep cycle batteries may/usually require a different charger then a starting battery, depends on further research to keep up with the times.
And about David 9 boats, the ninth one, web search "Sergeant Lewis trimaran"

David 9 boats
New Poster
New Poster
Posts: 4
Joined: Sat Jan 01, 2022 2:13 am
Location: Oregon

Re: Main Fuse on Battery

Post by David 9 boats »

Ok! After some research, that Blue Seas 5511 On-Off switch for two separate batteries is ok, if that is how you operate your boat. On for the day, off to go home. Folks who like to stay out overnight may want to cut power to the motor. Or turn the motor off to clear a fouled prop, but keep the house turned on. Just to ask, has it become a problem these days that outboards are shorting out? If you have to fuse, should not the fuse be equal to the crank amp rating of the starting battery? Another point, mount cut-off switches in plain sight.

Post Reply

Who is online

Users browsing this forum: Ahrefs [Bot] and 8 guests