Battery circuit breaker on negative terminal

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Jul 22, 2021.

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  1. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    Easier to accommodate 300 amp breaker there. How about mount breaker to battery box side. From breaker would run to negative buss bar for all banks
     
  2. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    I am talking about a large breaker, not a small fuse. Simply to protect big battery cables to battery selector switches and the starter. Not small amp devices which have fuses and breakers on their positive wires. This 300 amp breaker to connect to negative battery terminal with about 5 inches of wire. Logicly,
    I cant find any fault with the idea. Putting this breaker on positive terminal is not easy to do
     
  3. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Sorry, no can do.

    [​IMG]

    https://www.bluesea.com/support/articles/Circuit_Protection/98/DC_Circuit_Protection
     
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  4. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    I do an overcurrent high amp fuse on all my boats in addition to positive side.

    Had a dual belt alternator blow a belt 80 hrs after a maintenance regimen, it half blew flopped out and sucked up a ground terminal from the back of the alternator into the remaining belt. Created a big ol dead short and smoked all the ground wires on the boat about 80 miles west of Sandpoint Alaska. Thankfully it was a mechanical engine and we managed to get it up and moving without any 12v. Steering mechanical and shifting by yelling in the engine room. Managed to limp in and spend 5 days with all hands rewiring the boat. It smoked wires 50 feet away. Five days and 2500 in wire.... every boat since has had negative ground, might be suspenders and a belt.... but I'm to far from home a lot of the year.
     
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  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Do you think that 300 amp will do the trick for the starter motor. At start up the motor amps will spike. With a fast acting breaker and other 12 volt draws, 300 may not be enough.
    Just wondering
     
  6. missinginaction
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    missinginaction Senior Member

  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    You mean a negative side fuse, not ground I think. Great story..

    I get why, but the guy is trying to avoid fusing the positive and he can't. I don't understand why he can't. He should be able to mrbf. Unless start batt..
     
    Last edited: Jul 23, 2021
  8. Barry
    Joined: Mar 2002
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    Barry Senior Member

    I noticed on Phil's diagram that the starter circuit does not need overload protection which makes a lot of sense as the starter motor draw becomes distinct from any other amp draws on your boat. Ie the battery can provide much more current
    than the 300 amp breaker limit that you are proposing.

    A couple of assumptions, possibly not accurate as I do not know the size of the motor, diesel or gas, age of the starter or the rest of the circuits in your boat that you might be using.
    So for discussion purposes only:
    1) Assume that you could see 80 amps of circuit consumption at the time that you want to start your engines
    2) Assume that the start up amps of your starter motor, ie initial engagement amp spike is ( 6 or 8 cylinder diesel) 300 amps dropping to 250 for 60 seconds

    A couple of scenarios
    A) With your 80 running amps and 300 initial start up spike you will exceed the 300 amp range and trip your proposed 300 amp breaker and lose all 12 volt power source in your boat.

    B) With the 80 amp circuits wired in parallel to the 300 amp starter circuit, the remaining circuits will be operational and you may or may not trip the 300 amp breaker is this is wired into the start only circuit.

    The battery selector switches do not need protection and the intermittent high amp starter circuit is limited in a long term "on" position as the solenoid is intermittently controlled by the operator .

    Phil, as a breaker is not needed on a start circuit to satisfy ABYC rules, and if you only put in a dedicated breaker on the start circuit, (not within the 7 inch proximity) anywhere along the line, would this make the breaker non-compliant?
     
  9. Ike
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    Ike Senior Member

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  10. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Hi, no, it is not commercial.
    the MRBF fuse sits up close to 2 inches, the battery box lid wont fit, I just dont like the way they designed those fuses because they are too tall.
    For a breaker idea, this here?
    2013 Cooper Bussmann Transportation Full Line Catalog (solar-electric.com)

    If the engine starter initial draw is 500 amps, then as it spins is around 200 amp. It seems this breaker would work ok as it does not take that long to crank before the engine fires up? Typically, my boat engines start up in less than 5 seconds. The chart seems to be saying breaker at 200% rating of 400 amps drawn would still give 15 to 30 seconds of run time before tripping.

    I would prefer a 300 amp breaker, but not finding a name brand.

    Any ideas about if this could work, or a 300 amp decent breaker?

    I can run a short wire to this breaker maybe 7 inches, don't know but 9 or even a foot would be better, then mount the breaker on the plywood bulkhead right in front of the battery boxes. Then other side of breaker would feed the starter selector 3 lug switch.

    upload_2021-7-26_13-57-59.png
     
  11. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    Amazon.com : attwood 9084-1 Large 29/31 Series Vented Marine Boat Battery Box with Mounting Kit and Strap, Black, Black, One Size (9084-1) : Sports & Outdoors

    I put a BCI 29 and BCI 31 battery in this box, and there is no room to add another 2 inches for the terminal fuse, the stud sticks up 1.75 inches, it's too tall, the lid cant fit down to hold battery as it should. If you could lay a terminal fuse over on its side, then it could fit. Like take a copper plate and twist it 90 degrees idea. Bolt terminal fuse to the twisted copper plate.

    So that sort of leaves me with using a fuse holder or breaker mounted a few inches away from the battery box, if I want to use the lid, which I do.

    Maybe you could cut out a hole in the lid for the fuse t0 stick up out of, seems like a bad idea to me.

    With my thick stiff 4/0 wire on the positive post, I had to cut the box lid almost to the top to clear the wire. So when lid is installed, the top of the wire almost touches the top of the box. That tells me with a MBRF fuse holder, the lid wont clear it.
    The stud sticks up 1.75 or about 2 inches, I estimate the current wire sticks up around an inch. If the 4/0 wire is then bolted to the top of the fuse, its going way too high. I would have to really gouge out the lid above the wire connection to allow it to fit, is that what people do?

    I suppose if the wire was flipped over, so the offset lug was pointing down, it would have more room, but dont know if the flipped lug would fit the fuse holder and still it too tall as the mount stud is almost 2 inches tall.
    [​IMG]
     
    Last edited: Jul 26, 2021
  12. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    here is a pic of what I am dealing with. Recently ran big wires to the gen to use the start battery versus buying another start battery for gen. So now I have 30 feet round trip to where gen sits, meaning a lot more positive wire exposure to potential shorts, not that I expect any, so been thinking of breakers or fuses for the start battery.

    You can see, start battery bank is on the left, and is controlled by the left rotary switch, house bank on right controlled by right rotary switch. House bank is fused for 500 amps to inverter, 150 amps house, 100 amps lectrasan head. I have not put the GC15 batteries in their box yet.

    well, cant post picture... here is a shared link
    https://photos.app.goo.gl/ZiTjwCHzb8P18rRH7

    Picture shows start battery positive wire upper left corner, and it is right up to top of the battery box lid. I pulled down rotary switches to explore ideas about fuses, etc...
     
  13. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    Hi, well breakers dont instantly trip unless 600% of rated loads, (really about 1 second.)
    Engines are like big block v8 with wound field coils, no magnets. I read initial instantaneous surge is maybe 500 amps, then as engine is spinning on starter, draw is anywhere from 200 to 250 amps.
    Starter bank is separate from house bank.
    I put some of the smaller wires which are fused anywhere from 9 inches to 40 inches away in ENT conduit.
     
  14. fallguy
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    fallguy Senior Member

    Well, those lids sure can be a pita. But they also just kinda rest there. The abyc requirement is no movement and no acid spilling (essentially), so, you could put a piece of wood on top of the battery and still ise it, although the strap might be short (ask me how I know). Anyhow, mrbf and don''t forget 1/8" more for the boot to avoid a short when the lid is off.
     

  15. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    The lid is designed to hold the battery down, if you use the box as they intended. The strap is secured to where box sits by these plastic things, the strap passes under them, the box is not screwed down to its base. Straps pass over lid to keep lid on and in effect then the battery stays in the box for when your boat rolls over, turns upside down.

    I did decide to buy a 300 amp ANL fuse holder made by Blue Sea, and buy a Blue Sea 300 amp fuse. The fuse holder cost me Amazon points and was an Amazon Warehouse deal at $16, so was free, the fuse amazingly was $14 but will take 2 weeks to ship. I use a Chase Amazon credit card, so earn points.
    Here these are
    Amazon.com: Blue Sea Systems ANL Fuse Block with Insulating Cover - 35-300A (5005): Sports & Outdoors
    Amazon.com: Blue Sea Systems-5133 Fuse ANL 300-AMP: Automotive

    A Busman fuse is the same fuse, and found a site that has lower prices, but dont know about shipping.
    Fuses Unlimited - Part Search - ANL
    You cant use the cheap ANL car audio fuses, they are maybe going to explode when they blow, seen pictures by MaineSail on a forum. Other thing is cheap ANL fuse holders, the plastic may melt, and the cable covers may not be big enough for 2/0 wires. Plenty of them talk of single 0 wires, 2, 4 gauge but not 2/0. The Blue sea fuse holder is rated for 300 amp, but the base plastic is the same material as their 750 amp model of holder. The diff is the 750 amp model can easily hold 4/0 lugs with the cover on, so you can put a bigger fuse in the 300 amp model. Starter wires are not continuous use, so they can take amps more than rated for short time of cranking, means for me, I would up the fuse to 400 amp if I had an issue with blowing fuses.

    Last night I realized if you bent a short copper bar at 90 degrees up and drilled 2 holes in the ends, you could flip a Terminal Fuse on its side and have it work ok to clear a box lid.

    I am also going to move my RED crossover power wire from switch down to the start electric gang block. If the ANL fuse blows, I cant start the engines, but if I move switch for the house bank, I can give unfused power back to the start electric gang block.

    That really is a possibility, one way is if your batteries are down in voltage, cranking efforts will be delayed and current flow increases.
     
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