fuse size

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rosewood

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was going to connect my two house batteries so i have double the amps but stay at twelve volt. i know i need to fuse the wires between each battery but not sure of the size of fuse. both the leisure batteries are 110 amps. any ideas please folks
 
rosewood said:
was going to connect my two house batteries so i have double the amps but stay at twelve volt. i know i need to fuse the wires between each battery but not sure of the size of fuse. both the leisure batteries are 110 amps. any ideas please folks
Click to expand...

the batteries must be connected in parallel; positive to positive and negative to negative.

Is not usual to fuse the interconnections but it is advisable to fuse the connection to the boat services.

The fuse obviously must be large enough to carry the maximum expected current but all wiring connected must be rated to safely carry a current no less than the fuse value.

Note there is a "special" way of connecting to a pair of batteries in parallel to ensure both are equally loaded and charged. The positive connection is made on one of the pair and the negative on the other.
This is shown diagrammatically here

scan0020.jpg
 
VicS said:
the batteries must be connected in parallel; positive to positive and negative to negative.

Is not usual to fuse the interconnections but it is advisable to fuse the connection to the boat services.

The fuse obviously must be large enough to carry the maximum expected current but all wiring connected must be rated to safely carry a current no less than the fuse value.

Note there is a "special" way of connecting to a pair of batteries in parallel to ensure both are equally loaded and charged. The positive connection is made on one of the pair and the negative on the other.
This is shown diagrammatically here

scan0020.jpg
Click to expand...

thanks for that. much appreciated
 
rosewood said:
was going to connect my two house batteries so i have double the amps but stay at twelve volt. i know i need to fuse the wires between each battery but not sure of the size of fuse. both the leisure batteries are 110 amps. any ideas please folks
Click to expand...

Electrickety is simple enough at the 12vdc boat level but so many posters seem not to fully grasp the terminology and cause confusion to themselves. At the risk of opening a can of worms and being flamed for pedantry, here goes.......

Batteries hold charge (or don't when they are flat). The SI unit for charge is the Coulomb (named after the French rugby stadium). The Ampère (also French) is the SI unit of current and is a dynamic quantity being defined as a coulomb/second. 'Cos the Coulomb is a bit small for describing batteries - 396000 Coulombs are in a fully-charged 110Ah battery - it is common parlance to describe the charge holding capacity of batteries in Amphours (1Ah=3600 Coulombs). The battery's charge holding has very little to do with how much current flows which is almost totally dependent on what equipment loads are connected to the battery. Ohm's (a German this time) Law defines the relationship between voltage (Volta was an Italian), current and resistance in a circuit but to make things easier most equipment is described by voltage (12vDC) and the current flow requirement. That all the original work on electricity was done by Johnny-foreigner probably explains the reluctance of Anglophones to use the correct terminology.

So for the OP, it doesn't matter how big or how many batteries he has, as long as they are connected in parallel. It is the load that he needs to know to specify the fuse size.
 
awol said:
Electrickety is simple enough at the 12vdc boat level but so many posters seem not to fully grasp the terminology and cause confusion to themselves. At the risk of opening a can of worms and being flamed for pedantry, here goes.......

Batteries hold charge (or don't when they are flat). The SI unit for charge is the Coulomb (named after the French rugby stadium). The Ampère (also French) is the SI unit of current and is a dynamic quantity being defined as a coulomb/second. 'Cos the Coulomb is a bit small for describing batteries - 396000 Coulombs are in a fully-charged 110Ah battery - it is common parlance to describe the charge holding capacity of batteries in Amphours (1Ah=3600 Coulombs). The battery's charge holding has very little to do with how much current flows which is almost totally dependent on what equipment loads are connected to the battery. Ohm's (a German this time) Law defines the relationship between voltage (Volta was an Italian), current and resistance in a circuit but to make things easier most equipment is described by voltage (12vDC) and the current flow requirement. That all the original work on electricity was done by Johnny-foreigner probably explains the reluctance of Anglophones to use the correct terminology.

So for the OP, it doesn't matter how big or how many batteries he has, as long as they are connected in parallel. It is the load that he needs to know to specify the fuse size.
Click to expand...

Blimey. Thanks for that. How do I work out the load?
 
rosewood said:
Blimey. Thanks for that. How do I work out the load?
Click to expand...

By adding together the current, in amps, each piece of equipment on the circuit will take. Where you know the power in watts but not the current calculate it from

amps= watts divided by volts

If the charge current goes though the same fuse although you wont add it to the above you will have to ensure that the fuse value exceeds the max charge current. You may have to take the max alternator output for this.
 
rosewood said:
was going to connect my two house batteries so i have double the amps but stay at twelve volt. i know i need to fuse the wires between each battery but not sure of the size of fuse...
Click to expand...

[1] You don't fuse the wires between the batteries.
[2] The main fuse should stay the same as your existing one, unless you upgrade the wiring.
 
nigelmercier said:
[1] You don't fuse the wires between the batteries.
[2] The main fuse should stay the same as your existing one, unless you upgrade the wiring.
Click to expand...

To be honest there is no fuse at all at the moment. It's a very old wiring set up and I am gradually trying to upgrade it. I even have two old fuse boxes like you used to get in your house. They seem to work mind you
 
rosewood said:
To be honest there is no fuse at all at the moment. It's a very old wiring set up and I am gradually trying to upgrade it...
Click to expand...

Then in the meantime you need to fit a fuse in the positive outlet from the bank, sized to suit the existing wire. To do this you need to measure it. We could probably get a rough idea if you could accurately measure the diameter of the copper core. Take note of any markings, and those on any crimped fittings.
 
nigelmercier said:
Then in the meantime you need to fit a fuse in the positive outlet from the bank, sized to suit the existing wire. To do this you need to measure it. We could probably get a rough idea if you could accurately measure the diameter of the copper core. Take note of any markings, and those on any crimped fittings.
Click to expand...
It's a pretty thick wire. Same dia as the one on my car battery. Should the fuse go from each battery in the bank to the on off both switch?
 
rosewood said:
It's a pretty thick wire. Same dia as the one on my car battery. Should the fuse go from each battery in the bank to the on off both switch?
Click to expand...

In which case rate the fuse to be just in excess of the maximum current that is likely to be drawn, or the maximum charge current, which ever will be the greater.

It will not matter that the wiring is much heavier .

It is conventional to put the fuse and the isolator switch in the positive wiring but there have been times in the past when for reasons which Sailorman will hopefully now explain, the isolator was put in the negative wiring
 
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