Need advice on battery cable fusing ect.

[bluey]

Hi,

I am getting closer to the stage where I can begin the wiring of my boat restoration. In the meantime
I've been studying the mountains of wiring advice on the internet but am still somewhat bewildered as
to which fuses I should use and where to locate them.

I will be using size 2/0 AWG battery cable which is 67.40m2 in cross-sectional area and need to know
which fuses would be suitable. I have studied several Ampacity charts on the web but they vary in their
current ratings for 2/0, some say 275Amps to 300 Amps and one even rated it as high as 400 Amps, so
this has me confused as to what size fuse I should get for this cable.

I've read in several posts that it's good practice to install a suitable high Amp fuse close to the battery to
protect the cabling, but that it's not advisable to have a fuse in the starting circuit. Well, this statement
has really got me wondering because I intend to have a duel battery setup with 3 way switch, and if I install
a suitable fuse in the House Battery circuit what happens when my Cranking battery is flat and I switch over
to the house battery to start the engine, does this not mean that I now have a fused starting circuit?

I am posting a diagram below of my setup which is fairly basic, and I'd be grateful if someone can advise me
on which fuses I should use and where they should be located.

What fuses should I use for size 2/0 cable?

Should there be a fuse in the 10 AWG wire from the starter to the ignition? If so what size
and where should it be located? Near the starter, or near the ignition panel?

Of course, any other relevent information you fellas could give me would be most gatefully appreciated.

Thanks,
bluey.

 

[Don S]

Re: Need advice on battery cable fusing ect.

I don't understand why you are using a battery combiner (aka ACR) and still using a 1/2/Both battery switch? You aren't isolating one battery for house and one for engine. You are just using one battery at a time for house and engine.

 

[bruceb58]

Re: Need advice on battery cable fusing ect.

As Don said, your battery setup is just 2 batteries. One is not devoted to house. Nothing wrong with that...that is how I have my boat set up. If you really want a set up that you have a separate house battery, you would need a switch like this one:

e-Series Dual Circuit Plus Battery Switch - Blue Sea Systems

Blue Sea Systems' Dual Circuit Battery Switch - Blue Sea Systems

 

[Don S]

Re: Need advice on battery cable fusing ect.

Marked up chart for wire and fuse sizes.

 

[Auger01]

Re: Need advice on battery cable fusing ect.

From the chart, it looks like a 200-300 amp fuse would be the right size. Circuit protection in the starting circuit is not required, but if you keep several spare fuses, it souldnt be a problem. Dont forget to also fuse the wires going to the combiner. Even the negative wire to the combine should be fused IIRC. The fuse sizes to the combiner should be specified by the manufacturer.

http://assets.bluesea.com/files/resources/reference/20010.pdf

 

[UncleWillie]

Re: Need advice on battery cable fusing ect.

There are No Fuse/Breakers in the circuits from the Batteries to the Starter.
Your schematic does not show any either.

The instant the Staring Solenoid closes and before the Starting Motor starts to rotate, the instantaneous current is Huge!
Currents well in excess of 1000 amps can be expected for a few milliseconds.
This would be indistinguishable from a dead short across the battery.
It would be very hard to design a breaker you would be able to afford to handle this situation.

 

[bluey]

Re: Need advice on battery cable fusing ect.

Don S,
"I don't understand why you are using a battery combiner...."

Thanks for the changes you made to my diagram Don, Can you tell me if there is meant be a fuse on the #10 wire that goes from the ignition switch at the instrument panel to the S terminal on the starter? There is none shown on the wiring diagram in my engine service manual. Regarding the combiner, it was included in my drawing as an afterthought because I read somewhere it was needed to stop an undercharged battery draining power from the other when switched to 'both', perhaps I misunderstood the concept. I would much prefer to save some money by not having one, if it's not necessary.
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bruceb58,
"....If you really want a set up that you have a separate house battery, you would need a switch like this one...."




Thanks for the information Bruce, I only want a setup that gives me a spare battery to use for lights etc when out fishing at night instead of draining my crahking battery. The boat will only have Nav lights, bilge pump and depth sounder so I didn't think it was necessary to have a dedicated house bank.
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Auger01,

Thanks for the good advice and the link to that Blueseas chart, I hadn't seen that one before.
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UncleWillie,
"....Currents well in excess of 1000 amps can be expected for a few milliseconds...."

The engine in my boat is a 2QM15 Yanmar diesel which has a 1.2Kw starter motor. There is no other indication of what Amps the starter draws, but going by the wire size recommendations in the service manual wiring diagram it seems they have allowed for a 200Amp draw. I know there can be a massive inrush spike well above this number and when trying to find information about it I was given a link to this video on Youtube which shows the spike to be 316 Amps which is not too bad. Of course, my engine might draw more or less than what is shown in the video so I do take your point, thanks for the information.

2QM Yanmar Inrush Starting Current - YouTube

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Many thanks for helping me with this one, fellas.

bluey.

 

[bruceb58]

Re: Need advice on battery cable fusing ect.

Thanks for the information Bruce, I only want a setup that gives me a spare battery to use for lights etc when out fishing at night instead of draining my crahking battery. The boat will only have Nav lights, bilge pump and depth sounder so I didn't think it was necessary to have a dedicated house bank.

I agree but your diagram had a house battery on it which is why I noted it.

You don't need or want a fuse on the cable going to the starter as both Don and Willie said.

 

[bluey]

Re: Need advice on battery cable fusing ect.

I agree but your diagram had a house battery on it which is why I noted it.

You don't need or want a fuse on the cable going to the starter as both Don and Willie said.

Thanks for the advice Bruce,

I guess I should have dropped the fancy names for my batteries and just called Battery #1 and Battery #2 .

Cheers.

 

[Don S]

Re: Need advice on battery cable fusing ect.

Can you tell me if there is meant be a fuse on the #10 wire that goes from the ignition switch at the instrument panel to the S terminal on the starter?

There is typically a fuse or circuit breaker on the motor for electrical power going from the engine the the B (Battery) terminal of the ignition switch. The wire going to the starters S terminal to the starter isn't fused, but is normally only operating a slave solenoid or relay.
Have no idea how Yanmar does it on that engine. You need to check the engines wiring diagram.

Regarding the combiner, it was included in my drawing as an afterthought because I read somewhere it was needed to stop an undercharged battery draining power from the other when switched to 'both', perhaps I misunderstood the concept.

You misunderstood. When the combiner is engaged, it does the same as turning the switch to both. Plus it's only designed to read on battery. So if you have your switch on say battery 2, and the A portion of the combiner is set on battery 1, then the batteries would never combine. Save your money, you don't need it. You would be better off with an isolator. But for your purposes, I don't think you need (or want) either.

At night, just use one battery, if it should get too low to start, just turn the switch to the other battery, start the motor and then turn it to both. Now you will combining both batteries and charging both.

 

[bruceb58]

Re: Need advice on battery cable fusing ect.

duplicate post

 

[bruceb58]

Re: Need advice on battery cable fusing ect.

Most combiners or ACRs are designed to read either battery. When either battery sees a voltage over a certain voltage( > 13V) it will combine.

With a combiner or ACR in the circuit, the only time you would ever use BOTH would be in an instance when neither battery has enough power to start the engine and you want to put the batteries in parallel as a last resort. The ACR or combiner will allow both batteries to charge no matter what battery position you are set to.