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chadwick02

protection between battery and alternator/starter

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chadwick02

Ronnie posting this picture (below) in another thread reminded me of a question that I have had for sometime now:

Why, on our boats, is there no fuse or circuit breaker between the battery and the engine (alternator or starter)?? I don't think I have seen one on any Malibu, and most diagrams (like posted below) do not include one either. It just seems like a bad idea to have, in most cases, 20+ feet of 2 or 0 gauge wire running the length of the boat side by side directly connected to the battery. If they were to fray on something, say the sharp edges of a pass-through hole in the fiberglass, and short out, there could be a serious problem. Blowup.gif

Or what if the voltage regulator were to go on the alternator? (although I suppose then it would just put out higher voltage and probably not trip the breaker?). It just seems like cheap and easy protection, so why not?

I just re-did my electrical system with the addition of my new audio system. It appears as though our starter draws about 90 amps while starting. Just to be safe, I put a 150amp breaker in the cable that goes to the engine. Can anyone think why this would be a bad idea?

post-5-1209996983_thumb.jpg

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crescentbar
Ronnie posting this picture (below) in another thread reminded me of a question that I have had for sometime now:

Why, on our boats, is there no fuse or circuit breaker between the battery and the engine (alternator or starter)?? I don't think I have seen one on any Malibu, and most diagrams (like posted below) do not include one either. It just seems like a bad idea to have, in most cases, 20+ feet of 2 or 0 gauge wire running the length of the boat side by side directly connected to the battery. If they were to fray on something, say the sharp edges of a pass-through hole in the fiberglass, and short out, there could be a serious problem. Blowup.gif

Or what if the voltage regulator were to go on the alternator? (although I suppose then it would just put out higher voltage and probably not trip the breaker?). It just seems like cheap and easy protection, so why not?

I just re-did my electrical system with the addition of my new audio system. It appears as though our starter draws about 90 amps while starting. Just to be safe, I put a 150amp breaker in the cable that goes to the engine. Can anyone think why this would be a bad idea?

post-5-1209996983_thumb.jpg

Might want to check near the battery boxes. We have a circuit breaker there. I think it's 80AMPs or something. It looks very similar to this one Link

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txwakejunkie

same here, we have a 60 or 80 amp breaker that looks to be factory.

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BlastRlxi

It's a 60 Amp circuit breaker that should be located close to the battery box.

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electricjohn

That breaker by the battery is the protection for the dash and assessories. You are right about starter protection though, none. One thing to consider is that the battery is current limited, usually a tad more than its CCA rating. If there was a short or fault on those wires, the amps the battery can put out is, as I said, limited and it would fall off very fast since the battery would be dying. The wire is without a doubt sized to ride that out without starting a fire. Now, those with multable batteries have something to think about.

edit: I wish I could spell.

Edited by electricjohn

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Pistol Pete

There's no circuit breaker or fuse in your car's wiring going from batt. to starter to alternator. In some new cars, the battery is in the trunk so, the cables run the same length as in your boat with way more possibilities of the wires fraying on something metallic. It's just the way it is. The cables are pretty tough and the more "connections" you put in the line, the more chance for possible problems.

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electricjohn

To add a bit from my previous post. There is a circuit breaker between the battery and alternator. It is the red button mounted on the right side near the back of the motor, or whatever side the starter is on. Power comes from the battery unprotected, then is tapped off of the starter and goes to that circuit breaker. IIRC it is a 50 amp klixon switch type overcurrent device. Fusing the starter would require about a 400 amp fuse. I will amp probe my starter this spring when I first start my boat and post the current draw. But that is still more than two or three weeks away. My boat don't come out till my oak trees are done pollenating.

edit for spelling

Edited by electricjohn

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Pistol Pete

I've measured the current draw on my starter and IIRC it's about 90 amps. Of course, that depends on the length and grade of the cables, batt. state of charge, and ambient temp.

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electricjohn

It has to be more than that. My 90 hp outboard draws more than that. I'm guessing 200+.

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chadwick02
It has to be more than that. My 90 hp outboard draws more than that. I'm guessing 200+.

I dont think so, although I dont have any "scientific" way to measure the draw. I had a bunch of random 12volt breakers kicking around, so I tried them, more for funzies than anything else.

First I tried my old stock breaker, which was a 60 amp. The starter tripped that instantly when I turned the key.

Then I had a monster brand 80 amp lying around from an old audio system, I installed that one and it tripped it the first time, but that was a long crank since I forgot i pulled the lanyard out. I started it 3 more times with the 80 amp and it only tripped once more ( 2 for 2).

I had a stinger 100amp breaker lying around, so I put that in there and it never tripped once. I actually spent a day on the water with the 100amp with out a problem. BUT, i felt that the 100amp was still cutting it a little too close, so when I built my audio system I just added an extra 140amp breaker for the engine lead. I figured a 140amp breaker should provide enough protection if a short were to happen, and also serves as an easy disconnect.

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electricjohn

OK, finally started the boat today for the first time this season. Yeah, I know, quite late in the season, but I have another boat that I use around here which is strickly for salt water. Fresh water season will start on Tuesday (7-22). Anyway, I measured the amperage draw of the starter today and came up with 140-145 amps. Initially it surges (inrushes) to 250 amps, but quickly drops off to the 140-145. This measurement was taken with a very accurate Hall Effect type clamp-on amprobe. My engine is the Monsoon. A few other measurements I took are....blower motor=4.9 amps, bilge pump=.9 amps. fuel pump=6.8 amps when priming-4.9 amps with engine running. The alternater initially was putting out 30 amps after the engine started and dropped off to 5 amps within a half minute.

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Sunsetter95
OK, finally started the boat today for the first time this season. Yeah, I know, quite late in the season, but I have another boat that I use around here which is strickly for salt water. Fresh water season will start on Tuesday (7-22). Anyway, I measured the amperage draw of the starter today and came up with 140-145 amps. Initially it surges (inrushes) to 250 amps, but quickly drops off to the 140-145. This measurement was taken with a very accurate Hall Effect type clamp-on amprobe. My engine is the Monsoon. A few other measurements I took are....blower motor=4.9 amps, bilge pump=.9 amps. fuel pump=6.8 amps when priming-4.9 amps with engine running. The alternater initially was putting out 30 amps after the engine started and dropped off to 5 amps within a half minute.

Great info ejohn...

Just thinking, if your pos battery cable should some how get frayed, and touches what ever, unless there is a complete circuit to ground, there is not issue. Granted it is not something that I want to see, but the boat does not provide a ground to complete a circuit. Where my cables go it would be pretty hard to fray and cross the pos cable and a bare ground. I would think the the breaker is just for thermal protection to not overheat and melt a cable in case of a starter malfunction. The pos is the one that could melt, it carries the load.

Am I off base here... what do you think Pete?

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Pistol Pete

You're right Doug.

What most people aren't thinking about with this issue is the fact that in a car, anything that is metal is grounded. But, in our boat's almost nothing has a path back to battery ground. No metal parts on the boat except the engine and drive line have a path to ground. There may be ways to path to ground behind the dash because of buss bars and all the wiring back there (i.e. chaffing) But, the rest of the boat is all bolted to fiberglass, plastic, or rubber, none of which will conduct electricity.

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