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Old 05-08-2016, 10:56   #46
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Re: Fused battery connector Up to the task?

Quote:
Originally Posted by Cadence View Post
Fuses are subject to vibration. As I said, not having one on the engine battery cable is JMHO
Yes they are but properly torqued connections and, if there is a concern for corrosion or loosening from vibration an application of the appropriate goop to the threads or connection (which should be standard protocol for any and all important nuts, bolts and connections on a boat) and the slight chance of a problem is solved.

Read the post prior to yours from Maine Sail. My experience parallels his. I have in the past had starter problems when I was trying to be a long distance boat owner and wasn't totally on top of maintenance, due to loose or corroded connection on the starter or solenoid. So far have never had a problem with a bad connection on a fuse.

I do agree 100% that it is good practice to have the engine ready to fire up reliably on short notice, just in case. I do not see a properly installed fuse on the starter circuit an issue with this requirement. Also, as I mentioned, my setup allows me to use the house batteries for emergency starting by turning one switch (two if I want to disable the dedicated starting battery). That is a very simple modification to the system and I think add a better and more useful backup starting plan than not fusing the starter cable.

Since it is good practice to occasionally check your batteries, connections, water (if you have non sealed batteries), etc it's very easy to check the fuse on the battery terminal at the same time.
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Old 05-08-2016, 12:21   #47
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Re: Fused battery connector Up to the task?

Whenever I see a bunch of guys on an Internet forum disagreeing with ABYC, UL or any other recognized standards organization, I tend to go with the recognized standards organization. They have the expertise and resources to figure out the right way to do things. No individual can match that knowledge and experience.

ABYC standards don't require circuit protection in a dedicated starting circuit but they don't prohibit it either. You can do either and pass inspection. If you choose to install circuit protection, you need to allow for the maximum current draw of the starter, not the normal draw. This would occur when trying to start the engine in really cold weather. The engine will be harder to turn and will likely turn for a longer time before starting. You don't want to have replacing a fuse complicate things.

Keep in mind that the battery is self limiting. It cannot produce an infinite amount of current because of its internal resistance and it cannot produce its maximum current for very long.
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Old 05-08-2016, 12:24   #48
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Re: Fused battery connector Up to the task?

Hey I don't understand the problem here. If you don't want to fuse a line on YOUR boat, don't! There's no need to spin some internet story around it, its' your boat!

I admit that I don't think my starter battery is fused (I admit I'm not sure either way and that there may be a fuse in line). I had never thought about it, but now that I have I'm going to be sure there is a fuse in the line. Since my start battery also goes to my windlass and generator there is lots of unseen cable that could just be waiting to become an issue and the cost of a fuse is cheap.
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Old 05-08-2016, 17:56   #49
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Re: Fused battery connector Up to the task?

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Originally Posted by rwidman View Post
Keep in mind that the battery is self limiting. It cannot produce an infinite amount of current because of its internal resistance and it cannot produce its maximum current for very long.
Not infinite but a shorted battery can produce a couple thousand amps, up to 5-6000 if I recall from CharlieJ's data. With a typical cruiser's battery bank there's enough amp hours to do this for several minutes, assuming something doesn't melt, catch fire or blow up first.
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Old 05-08-2016, 19:27   #50
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Re: Fused battery connector Up to the task?

Quite glad for the hijack really. I'm learning a lot from the discussion.

I bought some blue sea mrbf 200amp fuses to do the engine battery. Also bought the bluesea holder for the house bank, and just in case that won't fit, bought some anl fuses to try and get within 7" of the +ve terminal using my existing bep anl fuse holder

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Old 05-08-2016, 20:17   #51
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Re: Fused battery connector Up to the task?

Quote:
Originally Posted by rwidman View Post
If you choose to install circuit protection, you need to allow for the maximum current draw of the starter, not the normal draw. This would occur when trying to start the engine in really cold weather. The engine will be harder to turn and will likely turn for a longer time before starting. You don't want to have replacing a fuse complicate things.

Keep in mind that the battery is self limiting. It cannot produce an infinite amount of current because of its internal resistance and it cannot produce its maximum current for very long.
A Blue Seas ANL fuse will handle 150 to 160% of its rating for 500 seconds. They will handle a lot more current for shorter periods of time. I expect MRBF fuses to act in a similar way. As long as the starter circuit is wired properly - 2/0 for example - and fused accordingly there will not be a nuisance blow no matter how cold the start attempt is.

A battery is not really considered self limiting. Thousands of amps in a dead short very quickly.

A friend had an alternator wire short due to chafing immediately on starting the engines in a twin screw powerboat. Everything the alternator output wire touched was melted even though he shut down quickly. The alternator did not cause the high current, the start battery did. Took him quite a while to replace wires and control cables that were melted.
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Old 06-08-2016, 06:11   #52
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Re: Fused battery connector Up to the task?

For sure a long dedicated alternator wire should be fused right at the battery. All "non-start" load wires must be fused per ABYC. ABYC allows fusing of the start circuit.

A dedicated start battery typically does not have a lot of AH so a short can't last forever unlike a mains powered circuit.

For the record, a properly sized fuse at the battery for the starter circuit is not a big reliability problem. They don't often fail. But "properly sized" is very important here.

But a fuse is not a substitute for proper support of the cable including conduit if required. Also, it is not a substitute for following proper safety protocols when working around high current capable circuits. Disconnect the negative battery lead when using tools in an area where an accidental short is possible. Make sure that the + DC connections are covered to prevent accidental contact. Remove all watches, rings, necklaces, etc. when working near high current circuits. High current can injure and kill just as can high voltage.

Maybe we should start a thread on how to properly protect start circuits. Just putting in a fuse is not enough.

Maybe another thread on safe work practices on DC systems would be good too.
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Old 06-08-2016, 06:42   #53
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Re: Fused battery connector Up to the task?

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Originally Posted by transmitterdan View Post

A dedicated start battery typically does not have a lot of AH so a short can't last forever unlike a mains powered circuit.
It doesn't have to last forever. The wire will be red hot in a second or less.
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Old 06-08-2016, 09:39   #54
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Re: Fused battery connector Up to the task?

Here I think we are on the same page, with one comment (already made by mitiemp).

Quote:
Originally Posted by transmitterdan View Post
For sure a long dedicated alternator wire should be fused right at the battery. All "non-start" load wires must be fused per ABYC. ABYC allows fusing of the start circuit.

All correct as far as I know but I do have to say there are things not mandated by ABYC that I think are important to do on a boat.

A dedicated start battery typically does not have a lot of AH so a short can't last forever unlike a mains powered circuit.

Even a moderate sized starting battery will still pack enough punch to make some big sparks and melt stuff.

For the record, a properly sized fuse at the battery for the starter circuit is not a big reliability problem. They don't often fail. But "properly sized" is very important here.

Properly sized absolutely critical. Too small and you get nuisance blows. Too large and you aren't really getting protection.

But a fuse is not a substitute for proper support of the cable including conduit if required.

Absolutely correct. Don't use a fuse to justify sloppy wiring procedures.

Also, it is not a substitute for following proper safety protocols when working around high current capable circuits. Disconnect the negative battery lead when using tools in an area where an accidental short is possible. Make sure that the + DC connections are covered to prevent accidental contact. Remove all watches, rings, necklaces, etc. when working near high current circuits. High current can injure and kill just as can high voltage.

This is an area where I'm occasionally guilty. Seldom do I remove the battery cables although I do turn off the main switches which does disable everything except a small, always on circuit for a bilge pump with alarm and a small LED night light.

Maybe we should start a thread on how to properly protect start circuits. Just putting in a fuse is not enough.

Completely agree.

Maybe another thread on safe work practices on DC systems would be good too.

Not a bad idea. Since you thought of it I nominate you to start the thread.
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Old 06-08-2016, 10:24   #55
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Re: Fused battery connector Up to the task?

I have contributed my two bits. If you choose to fuse your starter battery, tape a spare on the cable. You don't want to be fumbling around for a fuse if you need the engine in a pinch.
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Old 06-08-2016, 11:02   #56
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Re: Fused battery connector Up to the task?

Post #51
Quote:
A Blue Seas ANL fuse will handle 150 to 160% of its rating for 500 seconds.
This is incorrect. An ANL fuse will handle 150% of its rating for between 10 and 20 seconds. Please review the trip curve here: http://bit.ly/2auA8pF

Quote:
I expect MRBF fuses to act in a similar way.
It does not appear that the MRBF is quite as sensitive as the ANL. Reviewing the MRBF trip curve for a 250A fuse, http://bit.ly/2aGJSQZ it appears that the curve has gone asymptotic, indicating that the time to trip is indefinite.
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Old 06-08-2016, 18:28   #57
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Re: Fused battery connector Up to the task?

Quote:
Originally Posted by Cadence View Post
I have contributed my two bits. If you choose to fuse your starter battery, tape a spare on the cable. You don't want to be fumbling around for a fuse if you need the engine in a pinch.
OR, wire your house batteries to post #2 on the starting battery switch so can use them as a backup for starting.
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Old 06-08-2016, 20:07   #58
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Re: Fused battery connector Up to the task?

Quote:
Originally Posted by CharlieJ View Post
Post #51

This is incorrect. An ANL fuse will handle 150% of its rating for between 10 and 20 seconds. Please review the trip curve here: http://bit.ly/2auA8pF


It does not appear that the MRBF is quite as sensitive as the ANL. Reviewing the MRBF trip curve for a 250A fuse, http://bit.ly/2aGJSQZ it appears that the curve has gone asymptotic, indicating that the time to trip is indefinite.
The way I read the trip curve shown below is that an ANL fuse will handle about 140% of its rating for 500 seconds.

I agree the MRBF curve is a bit odd though.
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Old 07-08-2016, 01:02   #59
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Re: Fused battery connector Up to the task?

Quote:
The way I read the trip curve shown below is that an ANL fuse will handle about 140% of its rating for 500 seconds.
The red band is where the fuse will blow. The bottom of that area appears to be parallel to the x axis so a load of about 140% will not be inside the red band will be supplied indefinitely. A load of 150% appears to enter the red trip zone at the knee between 10 and 20 seconds.
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Old 07-08-2016, 09:06   #60
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Re: Fused battery connector Up to the task?

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The red band is where the fuse will blow. The bottom of that area appears to be parallel to the x axis so a load of about 140% will not be inside the red band will be supplied indefinitely. A load of 150% appears to enter the red trip zone at the knee between 10 and 20 seconds.
At about 140 %. And it is flat to 500 seconds. Blue Seas used to state this on their web site, probably still do somewhere. I varies a bit depending on fuse rating. Some are as high as 160%.

I have not had any customer blow an ANL fuse during starting of the many I have installed.
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