Starter circuit breaker keeps tripping

[Mickeyrouse]

The mystery du jour is my circuit breaker on the engine starter. It is my understanding that ABYC does not require a circuit breaker from the starting battery to the starter. However, Nigel Calder’s book encourages circuit breakers on everything. So I have done that.
The engine in question is a Westerbeke/Usuzu 55 HP. The manual, which is in most cases generic to all of this family of engines, indicates that the draw could be as high as 265 amps when starting. The cable run from the engine battery to the starter is about 78 inches, using Ancor 1/0 fine strand tinned boat cable. Terminals are hydraulically crimped.
For years- 14- the 250 Blue Seas fuse (actually a Littelfuse) has seemingly been adequate. Once or twice when the engine had run several hours the fuse would blow if I stopped it and needed to re-start immediately.
After a couple episodes of this, I replaced the fuse block with a 300 amp circuit breaker. Recently I had the engine re-built (another story). The other day after running awhile we anchored, then decided to re-locate. The engine, quite warm, tripped the circuit breaker. After the engine cooled down, a couple hours, the engine started fine with the circuit breaker re-set. Under those conditions, the assumption that I can “ just re-set the circuit breaker” is not prudent.
So, my question: is my problem just an undersized circuit breaker, or is something else lurking in there?

[ItDepends]

Lots to extract from this...

Just to put this into perspective for you, I start a 74HP Volvo through a 125Amp MRBF fuse, and it has not failed in 6 years.

A warm diesel should be easier to crank, use less current, and start faster than a cold one. So, I am GUESSING that the location of your fuse/circuit breaker is actually in the engine room, and near enough to the engine that it gets quite hot when the engine is running. A very high ambient temperature will reduce the current required to blow a fuse or trip a circuit breaker. So get your circuit protection to a cooler location. That's one.

The other piece is that your cranking time SHOULD be very short. Normally if a diesel hasn't started in a second or two, something is wrong. You should be able to find a "time/Current" diagram for the fuse and the circuit breaker you used. I am betting you will find that the circuit breaker fails quicker at lower current flow than the fuse, even at the same or higher rating.

Combine that with a temperature that is too high, and you have exactly the problem you describe.

[Mickeyrouse]

To wit:
Circuit breaker is not in the engine compartment.

Breaker usually trips within a second. Engine usually starts within 3 seconds at most, usually faster.

[boatpoker]

Originally Posted by Mickeyrouse

To wit:
Circuit breaker is not in the engine compartment.

Breaker usually trips within a second. Engine usually starts within 3 seconds.

Westerbeke 55A Four ?

We run 300amp MRBF fuses on all our batteries, never had an issue.

[Maine Sail]

What brand model breaker is it? Most breakers are not designed to handle in-rush like an ANL, MRBF, or Class T do.. Also there are a ton of cheap breakers flooding the market right now that perform horribly and can actually be un-safe

[capt jgw]

I wonder if the starter could be going out. I had an old car once that would not crank if it was hot. Apparently the windings were shorting when hot and drawing more current. No fuse or breaker to trip, it just wouldn't crank. New starter fixed that.

[skipperpete]

Maybe it’s wise to reread your past threads where you had starting problems (with no mention of a breaker or fuse).... it’s even possible that you’re back to the original “water in the cylinders” problem that was the cause of the rebuild at that time.

[skipperpete]

And the original basic diagnostic still applies..........can you easily rotate the engine manually by using a breaker bar on the crankshaft pulley bolt[emoji780]

[Mickeyrouse]

Engine turns reasonably easy by hand with glow plugs removed to reduce compression. Had questions about the starter ( even tho its new) took it to a shop, checked out okay.
To Skipper Pete:water got in the cylinders 4 months ago after rebuild because I kept cranking before it started. Evacuated the water, engine started, runs fine, has since run about 15 hrs.
Re circuit breaker type: it’s something generic I found on ebay. If not suitable, would appreciate a recommendation. No disclaimers regarding type of service.

[stormalong]

Originally Posted by Maine Sail

What brand model breaker is it? Most breakers are not designed to handle in-rush like an ANL, MRBF, or Class T do.. Also there are a ton of cheap breakers flooding the market right now that perform horribly and can actually be un-safe

Maine Sail: Nice to see you posting. Hope you are doing well.

Others: Listen to Main Sail. A starter motor is initially a dead short as it starts moving. A circuit breaker has two ratings: current carry capacity and actual trip amps. A 300 amp breaker can carry 300 amps all day long but will trip as some higher flow which is also stated in the breaker specs.

Also, is 1/0 cable heavy enough? The voltage drop at 265 amps through the cable reduces the voltage and slows the motor. A stalled motor is again a dead short.

[Mickeyrouse]

Originally Posted by stormalong

Also, is 1/0 cable heavy enough? The voltage drop at 265 amps through the cable reduces the voltage and slows the motor. A stalled motor is again a dead short.

Well, I suppose nothing is heavy enough. But 1/0 was on the boat when I bought her 26 years ago, and I suspect she was launched with that gauge 49 years ago. When I rewired 15 years, I stayed with the same gauge but better grade. I frequently check it while running. It is never warm to the touch, though I realize that doesn’t rate as a scientific analysis.

[stormalong]

Originally Posted by Mickeyrouse

Well, I suppose nothing is heavy enough. But 1/0 was on the boat when I bought her 26 years ago, and I suspect she was launched with that gauge 49 years ago. When I rewired 15 years, I stayed with the same gauge but better grade. I frequently check it while running. It is never warm to the touch, though I realize that doesn’t rate as a scientific analysis.

I am talking about voltage drop, not heat loss. Since the wire is used for a second or two it won't get hot. Touching it while the engine is running means nothing. Wire resistance will always cause the voltage at the starter to be less than battery voltage. How much less depends on the wire size. And don't forget that you have two wires carrying the current so the path length is double.

[Bowdrie]

Originally Posted by Mickeyrouse

Recently I had the engine re-built (another story). The other day after running awhile we anchored, then decided to re-locate. The engine, quite warm, tripped the circuit breaker. After the engine cooled down, a couple hours, the engine started fine with the circuit breaker re-set

Ok, this is just a "shot in the dark", so to speak.
I'm not familiar with the specifics of your engine so I have a question about it.
Obviously, when the engine was rebuilt the starter motor would have been removed.
That said, does the starter use any shims to set the clearance between the pinion gear and the ring gear on the flywheel?, (or perhaps there is another method of setting engagement specs).
If so, and the clearance is too tight, (too thin of shim,) upon heat expansion the pinion and ring gear can be jammed together to the point that the gears do not want to rotate.
We're talking thousands of an inch; it takes very little to do this.
Then, upon the block/starter cooling down they contract, the clearance increases, and the gears become free to rotate without binding.
It might be worth looking into.
The Bendix has nothing to do with this, because the pinion has tapered teeth it can still be forced into engagement but will not turn the ring gear freely.
You might just loosen the starter bolts and see if the starter will move/rotate away from the engine a few thousands.

[Rumrace]

I’ve witnessed a starter motor push solder out of it. Most have absolutely no limit to the amps they will draw. The older dusty and worn the more amps they suck up. Fusing the power line is doom for sure. Putting a fuse on the battery should only be necessary if you have no battery charger on board. The charger should have fuses to protect the components.
The biggest problem with marine wire is folks adding stuff. I rewired a dinghy for a pal. Tiny boat with crappy wiring from previous owner and low grade unsupported wiring to the marker lighting. Boston whaler sure did a crap wiring job then 3 previous owners added stuff. Like $10.00 in scrap copper.
In this case the owner dropped in the battery backwards and blew the dash. The only thing which survived was ignition which is a separate and isolated circuit
You may be shocked how a cleaned starter and solinoid reduces amps. The carbon dust adds to ohms resistance just like a dirty distributor cap reducing combustion.
High amp and high voltage in line fusing really doesn’t make any sense.

[boatpoker]

Originally Posted by Rumrace

High amp and high voltage in line fusing really doesn’t make any sense.

Well you can take RUMRACE's advice or Maine Sail's ...
https://marinehowto.com/battery-bank...nt-protection/