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Re-wire project - Bus bar selection
I'm currently planning a partial boat re-wire, the previous owner had multiple circuits off the battery terminals and the 1-2-Both selector switch. Overall most of the battery cables are corroded (they were not heat sealed). I would like to start with a positive and negative bus, so I can properly add my battery monitor shunt (Simarine Pico).
My current setup is:
Yanmar 2GM20F with stock 35a alternator
2x Trojan T105 6v
1x Deka 12v Start battery
Heart Interface Freedom 10 Charger w/ 200A Class T fuse
Basic house loads, electronics, LED lights, freshwater pump, wheel pilot, and biggest consumer Novacool icebox conversion
I have done what I consider extensive research online, but I'm embarrassed that I'm stuck with a very basic question, what size (amps) bus bar do I need (what is the calculation)? A Blue Sea Common 150A, or up a level to a Blue Sea Maxibus 250A.
Thanks in advance, this is a great forum.
I've done similar research on projects and not found any good hard and fast guides.
I recently helped a friend of mine with a rewire on a smaller boat. Because I couldn't find any definitive guidance I think I stupidly oversized his bus bars.
For this situation I would look at your maximum potential load and I think I'd probably be more comfortable with the 250a option. Especially since the fuse in the inverter at 200a. That 200a fuse is there in large part to protect the wiring behind it. If it's at 200a and the bus bar is only sized for 150a there's potential for trouble before the fuse intervenes and breaks the circuit (though I suspect the 150a rating might be conservative I don't think there's any reason to test that theory).
So, to sum up my ramblings.... if it were my boat I'd almost certainly size up.
Although your house battery bank should never see a steady 250 amp load, I also agree that 250 amp rated bus bars should be used if you have the space. Although you didn't ask for other comments, having been where you are, you should also consider the following with your rewire project:
Install a USCG approved DC rated fuse in the negative cable between the battery negative post and the buss bar. The fuse rating should be about 4 times the greater of maximum house load or charging maximum current. It is important that the fuse be rated for DC service since DC arc interruption capacity are more severe compared to an AC circuit.
Every electrical cable used in your rewire project should use stranded tin plated copper, solid bare copper or bare stranded copper should be forbidden in a marine environment. I prefer teflon jacketed cable, however your ought size battery cable and any Marinco marine cable will have a PVC jacket.
Size all DC circuit conductors for max 3% drop (total round trip) at maximum current.
Connectors, use only ring lugs properly sized for the cable and stud/screw size and be tin plated with solid barrels. Do not use connectors with split barrels (automotive). Use PDIG "AMP" or T&B crimp connectors and a ratcheting crimping tool or swaging tool. After crimping connector to conductor, solder seal the joint to provide infinite life corrosion resistance to the joint. A heat shrink type crimp connector is far inferior to a crimped and solder sealed connector. Some may say that NMEA doesn't allow solder sealed connectors, which is true (NMEA means solder only connector to cable joint). The joint I recommend is a crimp then solder connection, which NMEA doesn't have any comment about and the US Navy specs for DC shipboard cabling.
On my boat I never use butt splices to join conductors.
Dry fit the cables and use T&B saddle clamps and zip ties (UV resistant). When you make the final assembly, use an acid brush to apply a thin coat of Dow Corning 4 Electrical Insulating Compound.
Install a reverse polarity detector, a galvanic isollator, and a new shore power cable AC receptacle (I prefer "SmartPlug"). Make sure your shore power AC cable uses tin plated conductors (most do not).
Give some thought to your DC and AC panel design, now is the time to change it. Make sure each AC circuit is a two pole type (switching line and neutral simultaneously).
By the way, your shunt should be located in the DC negative circuit between buss and battery post.
Before you start cutting cable, make an electrical schematic diagram and show the conductor termination ID on the diagram. When you fabricate the conductor, make sure to attach a permanent wire label with the ID at each cable end.
I hope you find this information useful.
Lots of valuable info here:
I have a sailboat with the exact same engine, and when I purchased her 3 years ago, the same alternator. I've gone through two major iterations of my power system, and am currently using a very well integrated Victron LiFePO4 system. I'm just about done with my first article on this new system and hope to publish in the next few days.
Part of that was replacing all of the bus bars and wiring. I chose Marinco's Pro Installer series bus bars because of space ( http://www.marinco.com/en/products/pro-installer) - they are all engineered to cross connect to each-other without lots of cabling. They essentially built everything the same height and sell link bars that allow you to do a lot more compact wiring and bus work without tons of extra cables - nice for space constrained sailboats!
One of the best sites in the world Ben Ellison already mentioned - RC's knowledge about wiring, battery banks, battery testing, and more is invaluable. I own the tools he cites on the page linked above, and absolutely love all of them. I have tried some of the knock off brands, and they aren't worth the time. Highly recommend reading not only how to make the cables, but his other articles as well.
I always oversize whatever I am putting in from the electrical side of things - this includes wire and bus bars. I also try to think if I will be upgrading/replacing something in the future, or adding more load/capacity and require something larger then as well - saving myself from doing it a second time. Depending on whether you choose to add a higher output alternator, switch to higher charge output charger, or even batteries that can accept higher charge, all of those factors could drive up the size.
I find the most helpful thing to diagram out the entire system on paper or computer and mark each device/cable/thing with what it consumes to help suss out the overall capacity required for wires, busses, and the like. Sometimes you can forget that one cable carries the load for more than what you think, and sizing those appropriately will save you headaches in the future!