Starter circuit breaker keeps tripping

[goboatingnow]

Use a fuse not a circuit breaker. A 300A will nuisance trip on a starter.

[wingssail]

Originally Posted by 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.

The account from the OP does not surprise me. For years we had a similar problem: The engine cranked very slowly when hot. It always started, but sometimes we had to switch the batteries to "Both". When cold the engine cranked easily.

We checked and serviced all the cables and connections several times.

Finally, over years, the cranking got slower and slower. We replaced the starter recently and things got back to normal, (starting was easy at all times).

Our old starter is in the shop getting re-wound.

(A lesson: cranking a hot engine with a low battery will cause lots of amps to flow through the starter, shortening its life)

[kish]

Use a fuse, not a breaker on a starting circuit.

The fuse protects the cable. It should never be called upon in a correctly wired system.


Don't use an off the shelf circuit breaker [not specified for multiple operations at its nominal rating] on a circuit that carries hundreds of Amps.

Not all breakers of a given Amp rating are the same.

There are many eastern "equivalents" on Amazon

Each circuit interruption that a breaker does will cause deterioration to its inner working mechanism.
Check out the breaker current/time operating curve.

A correctly rated fuse will be safer than a circuit breaker,
Check out its characteristic current/time operating curve.

[cr180]

Three points to make. 1) Motor “inrush” current is around 5X or more of running current. So your circuit is drawing approx 1500 amps for some period of time. 2) Circuit breakers are typically not intended to protect motors because of the high inrush current and can result in unintended nuisance tripping. In industrial applications, the breakers are over sized and separate thermal overloads are used to protect the motor. 3) A very strong case can be made for not having either a fuse or breaker in a boat starting motor circuit: The cables are short and can be visually inspected, and most importantly, priority is given to starting the engine for propulsion in emergency situations.

[boatpoker]

Originally Posted by cr180

Three points to make. 1) Motor “inrush” current is around 5X or more of running current. So your circuit is drawing approx 1500 amps for some period of time. 2) Circuit breakers are typically not intended to protect motors because of the high inrush current and can result in unintended nuisance tripping. In industrial applications, the breakers are over sized and separate thermal overloads are used to protect the motor. 3) A very strong case can be made for not having either a fuse or breaker in a boat starting motor circuit: The cables are short and can be visually inspected, and most importantly, priority is given to starting the engine for propulsion in emergency situations.

Having been (some years ago) An ABYC Certified Marine Electrician, I'd
prefer to take advice from someone with proven credentials ...
https://marinehowto.com/battery-bank...nt-protection/

[cr180]

Originally Posted by boatpoker

Having been (some years ago) An ABYC Certified Marine Electrician, I'd
prefer to take advice from someone with proven credentials ...
https://marinehowto.com/battery-bank...nt-protection/

Thanks. I’m also a fan of “marine how to”. And respect a Certified Marine Electrician’s experience. But a carefull read of the marine how to write up reveals that the over current device is there to protect the cable not the end device (starting motor). Also agree that a fuse can be properly sized large enough to protect the cable and also allow the starting motor inrush current. But fuses fail. So the trade off is cable protection for a short cable that is visible for inspection vs a spurious fuse failure vs priority for engine starting for emergency propulsion. Reasonably sure that is why the ABYC exception for not requiring overcurrent protection for engine starting circuits exists. My credentials: Electrical Engineer, BSEE, Registered Professional Engineer (and paid my dues working as an electrician as well).

As in all things in life, there are trade offs and risks. Think if alternatives are presented and adequately explained, then we can each make an informed decision.

[boatpoker]

Originally Posted by cr180

Also agree that a fuse can be properly sized large enough to protect the cable and also allow the starting motor inrush current. But fuses fail.

Did you read Rod's article down to the photo of the burned out boat with the battery that exploded due to lack of a fuse ?

Over 24,000hrs under power in my log and never experienced a "failed" fuse.

I have 40 or 50 photos of exploded batteries that would not have done so if fused.

We can agree to disagree, I'll go with Rod and my experience.

[cr180]

Originally Posted by boatpoker

Did you read Rod's article down to the photo of the burned out boat with the battery that exploded due to lack of a fuse ?

Over 24,000hrs under power in my log and never experienced a "failed" fuse.

I have 40 or 50 photos of exploded batteries that would not have done so if fused.

We can agree to disagree, I'll go with Rod and my experience.

Once again, thanks for your input. We have differing experience. Don’t know of any boat battery failures due to short circuits in engine starting service but personally have had several fuse failures over the decades boating. Most boats were originally supplied without starting circuit overcurrent protection in full compliance with ABYC. And it’s not that the builders wanted to cheap out, it is because the ABYC recognizes the importance of being able to start an engine when needed in an emergency.

[Mickeyrouse]

Update on tripping circuit breaker.
I am embarrassed to say I was incorrectly interpreting the behavior of the circuit breaker. It is a new (to me) type I have never encountered before, and is apparently designed to be used in switching. It has a button on top and a lever on the side. I’m thinking the button up-lever out means tripped, which is the opposite of what it means. Until I put the ohm meter on it I was thinking wrong. But I replaced it anyway with the Blue Seas 250 amp fuse and fuse block. Engine still didn’t crank.
So my buddy Hank comes down and saves me from myself. We checked for current at each connection point from the battery, starter, keyswitch, starter solenoid, etc. in the process of which- the engine cranked and ran. The tell tale sign was the oil pressure buzzer intermittently going off and on while the key was on. Checked the plugs of the wiring harness to buzzer and instrument-switch panel. Pretty corroded. Installed a new wiring harness a couple weeks ago and apparently the new harness disturbed surface corrosion on the contact pins. The harness plug was intermittently opening the circuit. Cleaned the male pins with sandpaper and the female pins with the Dremel burnishing tool running on slowest speed. Applied dielectric grease to the plugs. Everything starting and running fine now. Incidentally, we put a clamp meter on the cable from the battery to the starter. Starting a cold engine, it drew 162 amps.
Regarding condition of starter motor: It’s brand new this summer, and probably has less than 30 starts on it. Took it to a starter shop. The tech opened it up, says it looks brand new. As well it should. I am good at letting fear of a complicated solution obscure checking for the simplest thing first.
As computer reparmen used to tell me, they would always ask: “ Is it plugged in?”

[sinnerman]

I would replace the CB with a fuse.

You do not want a CB tripping when you are trying to start the engine in an emergency.

Cheers.

[double u]

I always was under the impression, that the max current the starter motor can draw was the CCA of the battery.

[Leighpilot]

Assume the circuit breaker is operating as designed. Check for shorts or other causes of heavy draw. If there’s nothing , replace the circuit breaker.

That should fix the issue. If not , well there was a problem you just didn’t find it.

Under no circumstances remove the breaker from the circuit unless you plan on making an insurance claim for fire damage b

[David Mathis]

Your starter is ready for a rebuild or replacement. Do it now before it fails at a critical time. The tripping breaker is your friend, it's telling you about a problem. Listen to it.

[steve1122]

A fuse or circuit breaker is always selected to protect the wire that is supplying whatever device you have connected to it, not the device itself. Since a 1/0 wire is rated 150A, the 300A breaker isn't going to provide the protection needed. If your load is really as high as you think, upsizing to a 00 wire would be a better approach.

[Wotname]

Originally Posted by double u

I always was under the impression, that the max current the starter motor can draw was the CCA of the battery.

No. Under almost all conditions, a battery can deliver way more amps than it's CCA rating.

The CCA rating (under the SAE standard) is how many amps a given 12-volts battery may support for 30 seconds at 0°F (-18°C) before the voltage drops to at least 7.2 volts. At higher battery temperatures and for shorter times, a battery can vastly exceed it's CCA ratings.


The DIN and JIS standards are slightly different but the concept is the same.