What Size of Fuse at the Battery

[wildernessdave]

Thanks thomm225 that sounds like it might be a good option for our set up as well. If others have ideas please let me know.

[wildernessdave]

Thanks thomm225 that sounds like it might be a good option for our set up as well. If others have ideas please let me know.

[rwidman]

Originally Posted by Fuss

...................... How many amps would a 50mm2 - AWG 0 cable draw when shorted. ..............

There's no answer to that question.

You need to specify the length of the cable from the battery to the short circuit and back. Look up the resistance per foot of the cable, total it all up and then use ohms law to find the current.

Realistically, your results will be theoretical because in real life, the battery voltage will go down under those conditions because of the internal resistance of the battery.

Again, in real life, forget about calculations, look up the ampacity of the AWG 0 cable and use a fuse of that capacity or lower.

[smac999]

Originally Posted by rwidman

Again, in real life, forget about calculations, look up the ampacity of the AWG 0 cable and use a fuse of that capacity or lower.

You've missed the point of his question. (Which was 7 years ago FYI...) This is real life. His 7k gen is fed with 0awg. You can't fuse a 7k gen at 200a. It will blow. Fuse at maybe 300-400.

Since abyc does not require a fuse. As far as I'm concered Putting a 400a fuse on a 2awg starter cable does not goes against abyc. And his question is will it still blow. If you dead short a 0awg wire with a 400a fuse. The best awsnwer is it's certainly a better chance of it blowing then not having one at all.

[KISS]

...duplicate post

[KISS]

In my understanding, the fuse should be rated 50% above the highest normal load on the wire (so you don't blow the fuse during routine use), but well below the rated amperage of the wire (so you don't melt the wire).

[rwidman]

Originally Posted by smac999

You've missed the point of his question. (Which was 7 years ago FYI...) This is real life. .......

He asked a question in plain English. I don't know how I am expected to understand some hidden point. If he meant to ask something else, he should have asked that. My answer is correct and I stand by it.

[rwidman]

The fuse can be the same rating as the conductor it's protecting. You can make it less with the risk of nuisance blowing.

[rwidman]

Originally Posted by smac999

You've missed the point of his question. (Which was 7 years ago FYI...) .

You apparently do not understand my post.

Read it again, slowly.

[boatpoker]

Originally Posted by djmarchand

John:

ABYC standards do not require a fuse or circuit breaker between the starting battery and the starter and it is not a good idea in any case.
David

One of the very few places I disagree with ABYC having seen the result of locked up starter motor. 800amps has to go somewhere ! it must always be remembered that ABYC Standards as they say themselves are a minimum not a maximum.
If you browse Mainesail's website (difficult to navigate) he has a photo that just may change your mind.

My starting battery will always be fuse protected

[sailorboy1]

Originally Posted by Fuss

I want to reduce the risk of a dc fire on my boat and I have no fuses at the batteries.
But I don't want to create any additional problems like blown fuses if I had a motor problem for example and spent a while trying to start my engine.

I have a 700a 24v house battery running everything including anchor and bow thruster.
The cable looks to be about 90mm2 - AWG 000.
What size of fuse do I need at the battery?

I have a 12v 135 hp 6 cyl diesel requiring 2 x 800 cold cranking amp batteries in parallel to start.
The starter cable is 70mm2 - AWG 00.
These same batteries are used to start my 3cyl 7kw generator
The starter cable is 50mm2 - AWG 0.

What size of fuse do I need at each battery?

Thanks for any advice
John

I'm going to sty out of the technical argument and stay with the practical

I have 150 amp fuses on my batteries, which is WAY below the rating of the cables but also WAY above any excepted load.

[camel2012]

Originally Posted by boatpoker

One of the very few places I disagree with ABYC having seen the result of locked up starter motor. 800amps has to go somewhere ! it must always be remembered that ABYC Standards as they say themselves are a minimum not a maximum.
If you browse Mainesail's website (difficult to navigate) he has a photo that just may change your mind.

My starting battery will always be fuse protected

You should have a battery disconnect switch to your engine. If UL approved they are designed and tested to break a typical 1,500 A max locked rotor situation. That situation is also one that happens while you are actively engaged with the boat (turning the key) so during the 30 s max or so that it takes you to recognize the event and shut the switch off, no damage would be done to your starter cables.

The fuse is fine of course but it does lower voltage at the starter which in certain situations may limit your ability to start the engine (safety concern), and fuses have a tenancy when regularly overloaded above rating for short time constraints to get a memory and later on nuisance trip when you don't want them.

Personally I would not fuse and instead sheath the cable with secondary protection against unintended ground short circuit through abrasion, but that's just me ..