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Maine Sail wrote:If you let me know your engine model and battery cable size I can tell you the size fuses that could be used.
For the ANL just make a 2GA jumper between the ANL and your + battery post. If you don't own a crimper just order one pre-made from Mike at Genuinedealz.com. Usually the + battery post is a 3/8" stud and the ANL is 5/16" but some battery manufacturers ship batts with 5/16" posts to so be sure what size lug holes you need and how long the jumper needs to be before ordering the jumper.
The fuse should be as close to the battery as possible. The ABYC wants to see it within 7" but this is very often unrealistic so as close as you can get it.
210A is the max at 100% cable rating and should be plenty for your engine. You can't however buy a 210A ANL so you'll need a 200A. You CAN however go to 150% of that chart if necessary. So if by odd chance you ever blew that fuse you could safely install a 300A fuse.
Rich, if my understanding of DC current is correct, the electrons do move from positive to negative. If you had the fuse on the negative side and the wire shorted to ground anywhere in the system, the fuse would do no good. You want to cut the circuit as close to the source of power as possible.
I don't believe the jumper is generally fused as it is a very short run between the batteries. The only protection a second fuse between the batteries would afford, would be to the jumper wire itself. The main fuse leaving the bank would cut the power from both batteries.
I did switch to the terminal fuses Maine Sail recommends and they are very nice and offer complete protection with a minimum number of connections. Remember to always carry spares, Steve.
Electrons have a negative charge and flow from negative to positive but that really doesn't make any difference for this discusion (see link below). For current to flow there must be a complete circuit. According to Kirchhoffs current laws the sum of currents flowing into a node is equal to the sum of the currents flowing out. If you consider the battery to be a node, the law basically says the current going into the battery is equal to the current going out. Likewise the current flowing through the series jumper would also be the same. I can't think of any single point failure mode that would not cause the fuse to blow no matter which location the fuse is located in.
What prompted this question is that it might be easier on our boat to do a fuse in the series jumper between the 2 6V batteries than either terminal. I'm curious what the ABYC says.
bottomscraper wrote:I'm curious what the ABYC says.
ABYC requires over current protection and switches to be in the positive wires not the ground or negative wires. Ground is not to be switched or broken per ABYC standards.
Will it work to break the circuit. Yes it will. Is it the preferred method, no...
So, what is the answer to Rich's question? Is it OK to put a fuse in the jumper cable connecting two 6V batteries in series? That cable is the positive from one of the batteries, but the negative from the other. It would certainly be easier to install on our setup.
Tom and Jean Keevil
CD33 Rover
Ashland OR and Ladysmith, BC
The purpose of overcurrent protective devices like fuses & circuit breakers is to protect wiring in the event of a fault. Faults can occur in loads (motor winding short circuits) or in wiring (shorts to ground). A good rule of thumb is to locate fuses & circuit breakers as close to the source (batteries) as possible but i don't think this is absolutely necessary. The most important thing is that the interrupt characteristics are such that the wiring is protected. Fast acting fuses and circuit breakers with magnetic trip mechanisms are designed to interrupt current before enough heat is generated by the overcurrent condition to challenge the wiring.
The above explanation may be a bit of a case of information without meaning. With respect to the question regarding putting a fuse on the series connection between two batteries, i would consult a reference book.
So, if there were a fault to ground in a circuit somewhere, with only one fuse in the jumper, the current from one battery would be cut off, but the other battery would continue to flow. So the fuse really needs to be after the second battery in the series. Is this correct reasoning? Thanks.
Tom and Jean Keevil
CD33 Rover
Ashland OR and Ladysmith, BC
No, if the fuse is in series with the fault, the fuse would interrupt the fault. Since you are proposing to put the fuse in the series link between the two batteries, it would most certainly be in series with any fault you could imagine. Having said that, i'm not knowledgeable regarding the recommendations of the ABYC.
