Fuse on negative battery lead

[Head Sail]

Last summer my engine would not start because of a blown 100amp fuse on the negative lead off the battery bank. The shop that found the problem said he had never seen a 100 amp fuse on the negative side. Anyone ever seen this before? The boat is new to me so something the PO did. It's a 89 Catalina 34 with a isolation transformer installed.
Thanks in advance.

 

[Maine Sail]

A 100A fuse is GROSSLY undersized for starting a sailboat AUX diesel motor. An ANL, Class T or MRBF fuse will do this for some time, due to trip delay curves, but will eventually result in a nuisance trip. The bare minimum I like to see on an M-25 is 200A but when ever possible I use 250A or up.. The fuse is always sized to protect the wire and the biggest fuse will always result in the least nuisance trips and the least voltage drop across the fuse.

It does not matter where in the circuit the fuse is, neg or positive, as to how it blows or protects, but here in the US the standards call for fusing or over current protection to be in the POSITIVE wire not the negative.. Battery bank fusing should ideally be within 7" of the positive battery bank post.

 

[Ralph Johnstone]

The shop that found the problem said he had never seen a 100 amp fuse on the negative side.

The poor PO was probably a little colour blind . Also, the fuse is a little on the light side for a starter motor.

 

[Stu Jackson]

Mark, please feel free to join us on the C34 Forum, in addition to actively participating here.

http://c34.org/bbs/index.php/board,11.0.html

Lots of C34-specific material available for you there.

 

[Head Sail]

Thanks all, that helps. Don't want to deal with another $1000 tow bill.
Stu, I'm also on the C34 site. Thought the question was not specific to C34s.

 

[Maine Sail]

Thanks all, that helps. Don't want to deal with another $1000 tow bill.
Stu, I'm also on the C34 site. Thought the question was not specific to C34s.

Do you mind if I use that quote above in one of my articles on proper fusing??? I can give you full credit, or leave you nameless.....

It is the little details that can cost owners BIG TIME and this is one of the best examples I have seen in a while.....

 

[Stu Jackson]

Thanks all, that helps. Don't want to deal with another $1000 tow bill.
Stu, I'm also on the C34 site. Thought the question was not specific to C34s.

Mark, that's great, good idea. Take Maine Sail up on his offer! :dance:

Actually, don't know what fuse you had there, but I always have backup fuses on our boat.

 

[Head Sail]

Mainsail, yes use it. If it will help someone in the future. Fortunately my insurance coved it 100%(credit to Amica).
I haven't seen any reference to checking this fuse if you have starting issues. In this case the fuse looked good at first glance but close examination showed a hairline crack. I was having slow starting issues when I first bought the boat so I replaced the ignition switch and start button which seemed to help but as usual, the problem resurfaced at the worst possible time.

 

[Stu Jackson]

Slow starting

Most often when skippers experience slow starting, they incorrectly assume it's the start button. Our experience has been it is usually the items discussed in our C34 Critical Upgrades topic, http://c34.org/bbs/index.php/topic,5078.0.html which include

--- rotten ground connection at the engine - check it, remove it, redo it, clean it up

--- bad fuse - your story, wrong position, incorrect sizing

--- bad fuseholder on the ignition wiring (hidden underneath the alternator)

MS and I have been "preaching" about the wiring harness trailer connections for years. This isn't "aimed" at you Mark, just advising other skippers.

 

[Head Sail]

Stu, the fuse is in the battery box under the starboard settee. On my boat it's about 7" from the negative terminal. I have 2 group 24s. If it has a hairline crack, intermittent or weak starting can result.

 

[Ron20324]

...I have 2 group 24s. ....

You might give seriouis consideration to upping the battery size. I went from 24&27 to 31's on my B323.

 

[Stu Jackson]

Stu, the fuse is in the battery box under the starboard settee. On my boat it's about 7" from the negative terminal. I have 2 group 24s. If it has a hairline crack, intermittent or weak starting can result.

Understood. But if it's really on the negative (no reason to doubt you) then per Maine Sail's guidance, I'd move it to the positive side and up the amperage. Sure, a bumfuzzle fuse, or any interruption in the circuit, whether + or - will do that. If it was my boat, I'd move the fuse and correct the amperage, as well as checking those things I mentioned (if you haven't already).

 

[Charles Erwin]

Maybe circumstances call for a 200 amp + Battery Fuse?

See http://www.bluesea.com/articles/640

Maine Sail will provide a picture because I have no clue how to do it.

Charles

 

[seadaddler]

Tow insurance

I have had Sea Tow since 2001 and has saved me many times and even used it out on a friends boat but had to say the owner was not on at the time but
it sea tow or boat us came in very handy with my first boat.
Nick

 

[arelic1949]

negative fuse<?>

Last summer my engine would not start because of a blown 100amp fuse on the negative lead off the battery bank. The shop that found the problem said he had never seen a 100 amp fuse on the negative side. Anyone ever seen this before? The boat is new to me so something the PO did. It's a 89 Catalina 34 with a isolation transformer installed.
Thanks in advance.

#one rewire- NEVER have a fuse on the negative side. if the fuse blows, the juice will find a way back to the battery: thru your shaft, rudder, or anywhere it can make a connection. #two buy calder's mechanical and electrical manual plus casey's this old boat books. used.read. repeat. good luck<.>

 

[Tom J]

Was the PO from Britain, perhaps? The Brits were famous for grounding the positive side of the battery and running everything off the negative side. Not that there's anything wrong with that .....