High amp fuses on engine starting circuit

[Joef]

I’ve started the rebuild of the 12vdistribution system on my dad’s B26. I found two giant fuses in the wiring between the battery switches and the starters. I assume they are there to protect the starting wiring in case of a serious short somewhere in that wire. I think those can be replaced w a modern high amp breaker. The old fuses labeling is worn off so I’m not sure what the amp rating is. Do I need to consider the alternator output, wire size starter or??? The cables are #2. Not sure what alternators are on those crusader v6.

Thanks
JoeF

[Ironworker]

Joe,

I use 300 amp fuses on a battery terminal like this

https://www.amazon.com/dp/B0019ZBTV4?re ... Bfuse&th=1

All battery circuits are fused based upon wire size and load. Keep a couple spares around. My rule of thumb is to use a fuse sized 25% to 30% larger than the load to stop nuisance fuse blowing.

A good resource on the web is Pacific Yacht Systems. I am happy to assist with the little knowledge that I have is you have questions.

[CamB25]

hmmmm...it's normally not practical to protect the high amperage wire from battery to engine starter. 600 - 1000+amps. Generally you keep the run short and the wire big to avoid issues. Even if you want to do it, a circuit breaker is not appropriate. #2 awg is really small for an engine starting circuit unless the run is very, very short, and then the need for protection is mute. The wire is the fuse. See ampacity table here: https://marinervwire.com/pages/marine-w ... d-ampacity.

It's normal to protect the charging current conductors - alternator to battery. Maybe that's the purpose for the fuses? But they would not be in the starting circuit. They may connect to the battery through the battery switch(es).

[Ironworker]

#2 awg is too small. It should be 2/0 maybe 1/0 could handle it but I'd go with the 2/0.

I am a fuse fanatic. Nothing worst than a boat fire.

These are the batteries that I'm using with my Cummins QSB 5.9 diesel engines. They are powerful and have high voltage tolerances which are very similar too a LiFePo charging profile.

https://www.interstatebatteries.com/products/31-agmx

BTW if you're interested in a Lithium House batteries Epoch is making a marine compliant battery that is reasonably priced

https://www.epochbatteries.com/collecti ... -batteries

I realize that I'm giving more info than you asked for but if you're rewiring your boat you might as well bring it into the future.

[Joef]

Thanks guys. Anything I do here will be an improvement.
The cable sizes seemed a little small but I was comparing to my old boat w 3208 Cats. This boat has crusader 4.3 gas engines. The wire run is short. We re going to use group 34 agm batteries and they are located just behind the panel.
You can see the fuse holders where I removed the fuses

[Joef]

Will try to repost the photo

[Joef]

Now that i see my own photo it’s hard to believe that almost everything worked. We’re going to replace it all.

This is a pretty simple boat. Two engines, three batteries. Three bilge pumps and some house loads that come off a small panel in the cuddy cabin. I found those BEP battery switch clusters w the VSR and parallel switches all built into a modular unit which would be a good start. Then a breaker for the house wire run to the cabin and helm… and three fuses or breakers for each bilge pump…. And a good grounding buss for all of the grounds.

Anyone have a good basic drawing/ design /photo ? I’m sure I can dream one up- but if anyone has one they’d be willing to share, I promise free beer if and when we ever meet!

[Joef]

Turns out we had the original Bertram manual- doesnt really show those big fuses. I’m sure someone did something at creative some point.

[Ironworker]

Check out this website for diagrams

https://www.pysystems.ca/resources/diagrams/

I'm shocked (pun intended) that anything worked.

[S Ritzert]

I am a PCM dealer, and crusader is in the PCM line. It may not have been then, but is now. PCM protected their circuits via a breaker mounted on the back of the engine. If it has one breaker, it was mainly for the charging system. I am assuming the age of your engines correlate with the age of the boat? Some folks can't wrap their head around splitting the systems. Usually anything off engine is that of the boat manufacturer. An example being, I have folks that will call and ask for a fuel filter for their (whatever engine) I always ask if it's engine specific, or is it boat manufacturer specific, or was it added after the fact? There are thousands of filters out there, so we need to know who put it on. I don't know if that makes any sense, but the moral of the story is, Who's fuses are those? I can tell you that crusader didn't use them. Did Bertram use them, or were they added by the consumer for extra protection?

The fuse Ironworker linked to, Mercruiser uses those in their start system. That fuse bolts to the starter, and the power wire goes on the other side. Defiantly keep a few spares if you go that route. I have seen that fuse ruin a weekend. I typically see those fuses fail when someone decides to wire a battery backwards.

I am a believer in circuit protecting everything that you can. Like Ironworker said, a boat fire is nothing to scoff at. If you want to protect the start circuit, I would use a breaker. You will determine breaker size, and wire size by amp load. You can determine amp load by reading the specs on the starter box. Relays also provide a level of protection. I would be more apt to protect the start side (switch circuit) of the relay than I would the main wire to the starter. Typically direct wires from the battery to the starter (or relay if you have one in the system) do not fail unless continually crank an engine that wont start.

[Joef]

Good point. At this moment , it’s impossible to say who put those in there . It doesn’t appear on the Bertram diagram and it’s def not a crusader part. My research deemed that ABYC does not require the starting circuit to be fused. It’s the only circuit on a boat that doesn’t have that requirement. However, many folks say that just because it’s not required doesn’t mean it’s a bad idea. I saw some videos w very experienced techs, engineers and naval architects… they are sort of split. Some say you def should Incase the starter shorts internally or a serious chafe in wire grounds out the circuit…. And one guy recommends that you put one in and oversize it since it’s not a requirement and you don’t have to match the fuse size to the wire size - and it would provide protection in case of a failure , even if some damage occurs.

Not sure what I’ll do but it will decide soon. If I keep the fuses in the new design, I’ll use an ANL fuse of a big enough size … also going to upsize the cables to 2/0 since I have some of that cable already from work I did on my own boat a bunch of years ago (I knew the extra would come in handy one day!)

But thanks for the input guys. Will keep you all posted

[CamB25]

When I launched my boat I kept blowing the fuse to the jackplate's hydraulic pump. Up sized, blew again, Up sized again, blew a third time. I called Bob's for advice. Their reply, "Don't use a fuse, everyone just runs it right off the battery!" The run from the fuse to the pump was less than 2 feet and I sized my original fuse and wire for the running current. But, exactly like an engine starter, the inrush current is very high and that's what blows the fuse. I now have an 80 amp fuse on that circuit, which is like having no fuse at all. (the 80 protects a sub fuse panel in the bilge and the jackplate is the only load on that panel.)

Moral: some loads are not practical to fuse. Ampacity charts are created assuming a continuous load. A starter motor is not continuous. 1000 amps for a second or two, or three. Use a big cable and keep the run short. Any fuse that can withstand the inrush will not protect the wire.

By all means do not use a breaker unless you like resetting breakers all the time. Unlike electric motors in a saw or blower, there is no capacitor starting help. It's just all on, right now, baby. Breakers can not handle that startup load....unless you use a huge breaker, but like the fuse, it's not protecting anything.

[Geebert]

Slow blow fuses are available for this type of circuit protection.
They'll blow quickly with a dead short, but can sustain brief overcurrent periods without blowing.

Also be aware of ignition protected components only in any area fumes can accumulate. This includes fuses and fuse panels. Some are and some aren't ignition protected.

[Tony Meola]

On a lot of the 31's, can't speak for the other models, the gas engines were hooked up to a circuit breaker. That was used to energize the starting circuit, same as turning an ignition switch on.

I do remember our boat having the same fuse blocks that you show in your picture, but if I remember right, they fused they fused the bilge pumps.