blown fuses

[Bobg]

2 years ago i installed 125 amp fuses on my battery banks (4 6 volt trojens) no problems however, this past week, both fuses have blown, i have tried to isolate the problem by shutting every thing off, then activating each piece of equipment while holding a dmv on my batteries to check voltage loss, all systems seem normal. I don't have a amperage tester. I checked the starter also and it seems ok.

I have bypassed the fuses in order to charge the battery bank,  then disconnected  the battery bank until new fuses arrive. at which that time i will test everything again and see what blows the fuse.  (but) these fuses are not cheap, would be nice to see if any one has a idea on what could be happening.  thank you

[Stu Jackson]

Bob, it could be a nuisance trip.

http://c34.org/bbs/index.php/topic,7770.msg53602.html#msg53602

[lazybone]

It might be easier to help you if we knew where the two fuses were located?  If they are on the alt or starter or both?
Size of alternator?  Size and length of wire.  Pos or neg side?

[Ron Hill]

Bob : I am assuming that these fuses are each on a pair of your 6V batteries? and that you have a duel output alternator? or otherwise you wouldn't have used 2 fuses ??

If my assumptions are correct, I'll guess that you have over amperage coming out of your alternator?  
Voltage regulator sending out too much field current?? - that's what usually causes that LARGE 125A size fuse to "blow".

Think you need to tell us a bit more about your charging system so we can give better advice.  
I also believe this may be more than just a nuisance.

A few thoughts

[Bobg]

Sorry it took so long to respond, havn't been by a computer for awhile.

I have a single internal regulated 90 amp alternator, AO goes to the house bank via a 6 gauge wire, From the house bank, (4 6volt trojens wired in series),  I have a 4 gauge wire going to post 1 on my perko switch, I used to have 2 4 gauge wires, one for each battery bank, but I connected all the batteries together, and disconnected (from the battery) one of the wires that used to go to the #2 post on the perko.
The wire that goes to the dp, is fused right at the batteries, and that is the fuse that has blown twice.
I have a promariner 20 amp charger with 2 fused #10 wires going to post 1 and post 2 on my perko switch,
from the (all) post, or C post, I have a #4 wire going to a post on my reserve battery on off switch, then to the starter solenoid, the other post on the on off switch, is connected to my reserve battery.  My combiner is also wired to the reserve battery switch, which effectivily combines all five batterys when charging.

my immediate concern, was that fused wire was some how chaffing against metal or something, but I can find no evidence of that.
I have to order more fuses to try and duplicate the problem through some trouble shooting, on that note are there any circut breakers out there I can put in the wire instead of those fuses?  Thaks guys for any help I appreciate it  Bob

[mainesail]

Sorry it took so long to respond, havn't been by a computer for awhile.

I have a single internal regulated 90 amp alternator, AO goes to the house bank via a 6 gauge wire, From the house bank, (4 6volt trojens wired in series),  I have a 4 gauge wire going to post 1 on my perko switch, I used to have 2 4 gauge wires, one for each battery bank, but I connected all the batteries together, and disconnected (from the battery) one of the wires that used to go to the #2 post on the perko.
The wire that goes to the dp, is fused right at the batteries, and that is the fuse that has blown twice.
I have a promariner 20 amp charger with 2 fused #10 wires going to post 1 and post 2 on my perko switch,
from the (all) post, or C post, I have a #4 wire going to a post on my reserve battery on off switch, then to the starter solenoid, the other post on the on off switch, is connected to my reserve battery.  My combiner is also wired to the reserve battery switch, which effectivily combines all five batterys when charging.

my immediate concern, was that fused wire was some how chaffing against metal or something, but I can find no evidence of that.
I have to order more fuses to try and duplicate the problem through some trouble shooting, on that note are there any circut breakers out there I can put in the wire instead of those fuses?  Thaks guys for any help I appreciate it  Bob

Sounds like you are starting the motor with a 125A fuse.. This is not an appropriate fuse for motor starting and it will eventually blow.. 200A minimum if you want to avoid nuisance blows..  The type of fuse also matters Class T, ANL or MRBF are the only fuse types to use for motor starting loads as they are designed for that with longer trip delay times..

[Fuzzy]

Bob:  you said that you have the batteries wired in series.
If that is not a misquote you are wired for 24volts and
not 12. This could cause the fuses to blow. The batteries
need to be wired in a series/parallel configuration to
Give you 12volts.
Larry

[Bobg]

Larry, I do indeed have my batteries wired in a series/parallel configuration. 

Main Sail, you said I need a 200 amp fuse, but it was my understanding that a number 4 wire directly off the battery post should call for a 125 amp fuse as per some schematics I have seen on this board. 
Yes I am starting my engine with the house batteries, (shouldn't that only take about 60 amps?) I only use the reserve battery (not fused) in case I need it.  Should I install  a 200 amp fuse there also?
As per your suggestion, I will order a 200 ANL amp fuse and go from there. (my 125 fuse is a ANL)

Your explanation must be it, because I can find nothing wrong anywhere. 

My trouble must have started when I combined all the house banks together, and ran one wire to the dp via the 125 amp fuse.  (as per the Jim Moe schematic)

Thank you all, very much appreciated  Bob

[mainesail]

Larry, I do indeed have my batteries wired in a series/parallel configuration.  

Main Sail, you said I need a 200 amp fuse, but it was my understanding that a number 4 wire directly off the battery post should call for a 125 amp fuse as per some schematics I have seen on this board.  
Yes I am starting my engine with the house batteries, (shouldn't that only take about 60 amps?) I only use the reserve battery (not fused) in case I need it.  Should I install  a 200 amp fuse there also?
As per your suggestion, I will order a 200 ANL amp fuse and go from there. (my 125 fuse is a ANL)

Your explanation must be it, because I can find nothing wrong anywhere.  

My trouble must have started when I combined all the house banks together, and ran one wire to the dp via the 125 amp fuse.  (as per the Jim Moe schematic)

Thank you all, very much appreciated  Bob

If the schematic you read calls for a 125A fuse and the bank will be used for starting the schematic is simply wrong. It WILL lead to nuisance trips.

Starting even an M-25 requires a LOT MORE than 60A...... 4GA Wire with a 105C rating can handle a max ampacity of 160A however the ABYC allows for 150% of this number for over-current protection which means 240A max. I would normally put a 225A fuse on #4 wire. That said ANY fuse is better than no fuse at all. I have done piles of testing on fuse trips and even with wire rated far below the ABYC safe max ampacity the fuses still trip in a dead short.

Here is 15' of 8GA wire tripping on a 400Ah LiFePO4 bank with a 300A fuse. The wire never even heated up..
http://youtu.be/y3gzhep8w4A

That said #4 wire is far too small and Catalina really cut corners here. Today, for the same size engines, they use 1/0 or 2/0 wire and have finally come into the 21st century....

While this is not an M-25 it gives a look at what can happen during cranking. This was at 32F on a Westerbeke 4 cylinder..


These are the "averages" during cranking as well as the start duration.

[Stu Jackson]

I've added "IMPORTANT NOTE ON FUSE SIZE" with a link back to this discussion on the C34 tech wiki article (Electrical Systems by Jim Moe).

[Bobg]

thank you mainsail, i do believe you got it figured out for me, very much appreciated I have passed this board onto other sailboat owners in my marina, no matter the sailboat brand, they all love it.  and thanks to the rest also  Bob

[Stu Jackson]

...I have passed this board onto other sailboat owners in my marina, no matter the sailboat brand, they all love it.  and thanks to the rest also  Bob

Bob,

Thanks for doing that.  Our goal has always been to share boat information.  Someone once mentioned that he/she thought there just wasn't enough "social stuff' on this Forum.  Many replied that if you wanna do "social networking" just use Facebook!     Not too bad an idea, but if someone wants to post about "get-togethers," there are other parts of the Forum via the "General Activities" part of the site.  There is also a "Boat for Sale" section.     Not that I'm ever going there...

Good luck, hope we've been able to help, which is what it's all about.

[lazybone]

Maybe the requirements for starter circuits have changed but as far as I know there are NO fuse requirements for protecting  the starter and its wire.

[mainesail]

Maybe the requirements for starter circuits have changed but as far as I know there are NO fuse requirements for protecting  the starter and its wire.

There is an "exemption" for starter circuits. However when most boaters start the engine with the house bank, or the house bank could be used in an emergency, then the fusing must be sized to accommodate starting loads. Also with a 1/2/BOTH as the factories ship with, and two identical batteries which is the "dedicated" starting circuit..?

There is no reasonable excuse to not fuse starting circuits on small AUX diesel engines. The exemption is designed for engines significantly larger than sailboat aux engines..

Course this is what happens when builder/people use "exemptions" as the rules..

This was a dead short in the battery cable, a few minutes prior and there were multiple 8 year old junior sailors on-board...




And fellow Mainer Nigel Calder agrees..


"The net result is that nowadays, electrical shorts are probably the number-one cause of fires on boats."

There is simply no excuse for not protecting all high-current circuits , including the cranking circuit."
Nigel Calder Cruising Handbook

[Roc]

I remember Mainesail posted a picture of the type of fuse that should be connected to the battery. Does anyone remember the posting?  I would like to visually see the hookup.

Thanks!