Circuit Breaker / Fuse for Starter(s)

[the MfM]

I know it’s not required but seems like it’s a good idea?

Last year I had a bearing go bad in one of the starters and it locked up. At first I thought it was one of the safety switches. By the time I realized it wasn’t a safety switch I had tried to crank the engine several times. And of course the cable to the starter (and the starter) had gotten quite warm to the touch.

Question is what size breaker... went to check current draw with my clamp meter and of course it’s batteries are dead.

Wiring is 4 gauge. Im thinking a 100 amp breaker should be enough to prevent nuisance trips and is well within the wires capacity.

Any reason I shouldn’t?

 

[Mainah]

Not sure how well that would work unless a correctly sized slow blow fuse or breaker. The start up draw to get the crank shaft turning is much higher than once the crank shaft is actually turning.

 

[the MfM]

If I knew the LRA of the starter it would be easy to size.

I was thinking of the blue sea 285 series.
https://www.bluesea.com/products/7188/285-Series_Circuit_Breaker_-_Surface_Mount_120A

They are good for 4-6 times more than there rating for short bursts.


According to their circuit wizard I could use up to a 150 amp breaker with the 8’ +- of four gauge wire I have to the starters. But I’d rather use the smallest breaker for the load.

 

[Julian]

I'd say for something that happens once every 18 years (per engine) I'd leave it alone.

 

[the MfM]

I'd say for something that happens once every 18 years (per engine) I'd leave it alone.

Because it’s 18 years old it makes sense to me to look at ways to prevent failure. If someone had kept cranking on the starter the cables could have easily melted or worse.

I replaced the starter with a $25 eBay special of unknown quality and I still have an 18 year old one in use. The same could happen again or potentially the solenoid could be rusty and decide to stick on one day. The boat has no battery switch. So no way to kill power if that were to happen.

Granted it’s unlikley to happen. But I’m adding a second battery and a switch. So for an extra $30 for a breaker while I’m at it seems worth the peace of mind.

I don’t see a down side to having properly sized fuse protection for the starters.

 

[Julian]

I don’t see a down side to having properly sized fuse protection for the starters.

Agreed that there isn't much downside by adding breakers other than them breaking and needing to replace them. I like to keep it simple where possible. Not seen many starter issues on the forum over the last 15 years so I'm not sure it is worth the effort to do, but as you said, it might save you replacing the 8' of 4 gauge wire in the future if you melt it.

 

[dan144k]

I installed these on my boat. One on each battery.
I originally installed 100 amp fuses, but they trippped from the starter. So then I installed 200amp, have worked without problem since 2013.

I ordered the base and 100 amp fuse form amazon, then the 200 amp fuses from www.ChartHouseElectronics.com. Dont know what current prices are.


TIFF] [Fuse Blocks Terminal Fuse Blocks
MRBF Terminal Fuse Block - 30 to 300A
5191

• Compact, high-amp fuse—appropriate for DC Main, inverter, windlass, and bow thruster circuit protection
• Provides high current protection in tight space constraints
• Ignition protected when used with Blue Sea Systems' MRBF Terminal Fuse
• Isolated stud design uses standard M8 hardware and permits stacking of terminals
• Insulating cap prevents accidental shorts
• Accepts 5∕16" ring terminals
• Mounts on 3/8” terminal studs
• Fuse sold separately

 

[the MfM]

I installed these on my boat. One on each battery.
I originally installed 100 amp fuses, but they trippped from the starter. So then I installed 200amp, have worked without problem since 2013.

I ordered the base and 100 amp fuse form amazon, then the 200 amp fuses from www.ChartHouseElectronics.com. Dont know what current prices are.


TIFF] [Fuse Blocks Terminal Fuse Blocks
MRBF Terminal Fuse Block - 30 to 300A
5191

• Compact, high-amp fuse—appropriate for DC Main, inverter, windlass, and bow thruster circuit protection
• Provides high current protection in tight space constraints
• Ignition protected when used with Blue Sea Systems' MRBF Terminal Fuse
• Isolated stud design uses standard M8 hardware and permits stacking of terminals
• Insulating cap prevents accidental shorts
• Accepts 5∕16" ring terminals
• Mounts on 3/8” terminal studs
• Fuse sold separately

I saw those and almost ordered them but I may have jumped the gun and ordered the 100 amp breaker. I’m going to put it on the output of the battery switch. That way I only need one instead of a fuse for each battery. If it trips I’ll use the breaker for the house loads bus bar. And try something else or just continue with no fuse.


Mercruiser uses a similar fuse block. But they put it on the starter solenoid. They list the same 90amp fuse for everything from 4.3’s to 7.4’ and for outboards up to their 350.

 

[dan144k]

@the MfM
I installed one on each battery, my thinking was if a cable goes bad I protect the boat from burning down.

My battery set up is simple. I us a simple switch and either choose battery 1 or 2 for the day, I try to alternate. The other battery is a backup.

On one of the batteries I installed a second bilge with a float, connected it directly to the battery, before the battery switch. For when I leave the boat in the water overnight during vacation.

The nice thing about the fuses is if you happen trip the fuse you can remove it. And carefully connect directly to the battery. To get to shore while monitoring things

 

[the MfM]

@the MfM
I installed one on each battery, my thinking was if a cable goes bad I protect the boat from burning down.

My battery set up is simple. I us a simple switch and either choose battery 1 or 2 for the day, I try to alternate. The other battery is a backup.

On one of the batteries I installed a second bilge with a float, connected it directly to the battery, before the battery switch. For when I leave the boat in the water overnight during vacation.

The nice thing about the fuses is if you happen trip the fuse you can remove it. And carefully connect directly to the battery. To get to shore while monitoring things

That’s pretty much what I’m planning to do as well. Except one circuit breaker instead of two fuses. I already have one bilge pump wired direct and plan to keep it that way. Everything else will go through the circuit breaker.


Raining so I made a mounting board to get started.

 

[the MfM]

Got it installed. And seems 100 amps is enough for my 2 strokes. Not that I ever it do but I was able to crank both engines at the same time without tripping the breaker.