advice what fuse for batteries

[arch007]

I have a 28 ft ssailboat with 3 lead acid batteries.

I wonder what fuse should I use ?

ANL fuse or MC 10 class T. What is MC 10 class T ?

Should I get a 300 amp fuse or 750 amp fuse ?

what does a engine starter usually draw ?

Thanks,

arch

[Sailmonkey]

How large are your battery cables?

How many watts is your starter (what engine)?

I prefer the blue seas terminal fuses myself

https://www.bluesea.com/products/519...k_-_30_to_300A

[double u]

afaik fusing the startercable is very difficult & never done

[Sailmonkey]

Originally Posted by double u

afaik fusing the startercable is very difficult & never done

Mine is fused.

Kubota d1105 with a 1000 watt starter.

300 amp fuse.....appropriate wire size, no problems.

[rwidman]

The ABYC does not require overcurrent protection (fuse, circuit breaker) in the engine starting circuit. The reason is, a value high enough to not open the circuit when starting the engine would not really provide protection to the circuit.


In simple terms, you do not need a fuse in the engine starting circuit. You do need a fuse or circuit breaker in any feed from the batteries to the main breaker or fuse panel.

[Sailmonkey]

Originally Posted by rwidman

The ABYC does not require overcurrent protection (fuse, circuit breaker) in the engine starting circuit. The reason is, a value high enough to not open the circuit when starting the engine would not really provide protection to the circuit.


In simple terms, you do not need a fuse in the engine starting circuit. You do need a fuse or circuit breaker in any feed from the batteries to the main breaker or fuse panel.

Nt required per ABYC, however if the engine is small enough, it's quite easy to provide fused protection.

However for a larger engine (I've never bothered to find the approximate displacement cutoff point) fusing is problematic.

Seeing as the OP hasn't responded with anything, we may never know if fusing the starter is a viable option for them.

[rwidman]

Originally Posted by Sailmonkey

........... Seeing as the OP hasn't responded with anything, we may never know if fusing the starter is a viable option for them.

And the other question is, what prompted him/her to post this question in the first place? Is he building a boat? Is he thinking the manufacturer of his boat forgot to put a fuse in?

[boatpoker]

Originally Posted by rwidman

The ABYC does not require overcurrent protection (fuse, circuit breaker) in the engine starting circuit. The reason is, a value high enough to not open the circuit when starting the engine would not really provide protection to the circuit.


In simple terms, you do not need a fuse in the engine starting circuit. You do need a fuse or circuit breaker in any feed from the batteries to the main breaker or fuse panel.

It must be remembered that all standards are "minimums" and I think ABYC dropped the ball here. This is an argument currently being discussed on the ABYC Technical committee and has much support on that committee. Mainesail agrees

My starting battery is fuse protected.
If your solenoid or starter freezes up or you have a short within the battery all those amps are going somewhere. On a small sailboat diesel I'd rather blow a 300amp fuse than send 300-800 amps somewhere else.

[rwidman]

Originally Posted by boatpoker

It must be remembered that all standards are "minimums" and I think ABYC dropped the ball here. This is an argument currently being discussed on the ABYC Technical committee and has much support on that committee. Mainesail agrees

My starting battery is fuse protected.
If your solenoid or starter freezes up or you have a short within the battery all those amps are going somewhere. On a small sailboat diesel I'd rather blow a 300amp fuse than send 300-800 amps somewhere else.

If you have a short within the battery, the fuse will do nothing. Actually, a short within the battery just means your output voltage is less. A shorted cell is a common mode of battery failure.

You would need to size your fuse to allow for the current the starter draws when starting a cold engine or you will have "nuisance" fuse blowing. There are occasions where being able to start the engine quickly is critical and you don't have time to replace a fuse, especially one that requires tools to replace.

Unlike power from the power company, power from your battery is limited by the internal resistance of the battery.

The ABYC people are pretty smart and have a lot of resources at their disposal. I'm going with their recommendations.

[boatpoker]

Originally Posted by rwidman

The ABYC people are pretty smart and have a lot of resources at their disposal. I'm going with their recommendations.

I agree they are pretty smart and I am ABYC certified but there is dissension within ABYC on this issue and supporters of the change include Mainesail (no longer on that committee) and Nigel Calder and some other well known names. I mention those two only becuase thay have published on the issue. I know several ABYC instructors who also agree but it's not my place to name them as they have not publicized their opinions. I'm betting on the next review of E-10/E-11 the requirement will change.

[Sailmonkey]

Originally Posted by rwidman

And the other question is, what prompted him/her to post this question in the first place? Is he building a boat? Is he thinking the manufacturer of his boat forgot to put a fuse in?

Our boat was not supplied with fuses on the battery leads. 42 years ago it wasn't done as practice. I added fuses as risk mitigation. Cheap insurance if you will.

Fusing the starter cable, if the engine is small enough, is also a no brainer for me as well. The 1000watt starter motor on our small engine makes fusing easy. Even with the start battery down to 8 volts the current draw is less than 70% of the fuse rating. All it takes is a little bit of chafe (reason enough to sleeve the cable) to cause a fire on a cable.

[arch007]

I asked because just bought a boat.

All the batteries are connected with no fuse. The main panel individual wires are fused.

It seems dangerous the batteries are not fused but did not know how high amps so will not blow with starter.

[Sailmonkey]

Originally Posted by arch007

I asked because just bought a boat.

All the batteries are connected with no fuse. The main panel individual wires are fused.

It seems dangerous the batteries are not fused but did not know how high amps so will not blow with starter.

So, what size engine? and what size cables from the batteries to the loads?

without these two pieces of information a guess can't even be attempted to what is the proper size of fuse, or if a fuse for the engine start battery is even practical.

[arch007]

Engine is a kubota beta 14.

All the batteries are connected in parallel so no one battery is the starter battery.

There are three lead acid batteries in all.

Not sure about size of cable to starter. Will checknext time at boat.

Thinking of the blue sea fuse block with 300 amp fuse.

[rwidman]

What is more important than overcurrent protection for the conductor supplying power to the starter (as I posted, not required) is overcurrent protection for the conductor feeding the main panel.

It's great that the individual circuits have overcurrent protection but it is also required for the wire feeding the main panel. Look on the wire for the size and then look on a wire capacity table for the correct overcurrent protection value.

You could do the same for the conductor supplying power to the starter if that makes you feel better. Just remember, if you use a fuse and it blows, you won't be able to restart your engine until you replace it. If you're drifting towards a rock jetty, this could be more of a problem than you had planned on.