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Old 12-03-2018, 18:38   #1
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Connecting Solar Controller: Wiring All The Way To The Battery?

hello,

i am revisiting my solar controller installation, and can't help wondering: the controller is a few feet away from the 1-2-both switch, and even closer to the massive negative bus connecting to the distribution panel. yet, i originally ran both pos and neg wires from the controller directly to the battery (with a fuse on the pos just before the battery), just like the controller manual suggested - and that's at least an additional 20' round trip of #8 wire.

what would be the issue with running these #8 awg wires just to the 1-2-both switch (so that it's #1 awg from there on) and the neg bus (and then it's 1/0)? i can put a fuse or breaker sized for the #8 awg wire running to those thicker ones.

sounds like it would be simpler, less of a mess, and less resistance. what am i missing, other than potential use case of being able to physically disconnect the batteries from all switches and what nots, while still charging them with solar?

the boat is a 38' sloop, house is 2 x group 27, starting is 1 x group 24 (which i'm going a size up to group 27 now), and the controller is a Morningstar. the battery box is under the cockpit floor and as much as i'd like to go with all GC2's, this is all that can possibly fit in the battery box: three 27's, i can't even go up a size to group 31.

thank you!
anton
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Old 13-03-2018, 07:42   #2
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

The switch adds two lugs and two connections, a fuse at the switch adds more connections. These all add resistance and contribute to voltage drop. I prefer very low voltage drop on charging systems. Without ratings on the Morningstar, I can't check wire charts, but I suspect 8AWG is a bit small. Rod Collins has posted a newer article about fuses and connections and voltage drop here;; https://marinehowto.com/fusing-termi...-voltage-drop/
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Old 13-03-2018, 08:03   #3
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

#8 fine strand is the thickest it will take. Would really running a #8 awg wire all the way (20 feet round trip) going to result in less resistance than #1 awg but with the two additional lugs of the existing battery cable?
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Old 13-03-2018, 09:05   #4
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

There is nothing wrong with doing it this way. Its always better to have the bigger cable carrying the current.

Doing it this way will not bypass the shunt which measures your + & - ah (if you have one) so it will properly measure your amp usage and yes, you will need to have a fuse to protect the smaller wire.
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Old 14-03-2018, 08:14   #5
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

Are you proposing to hitch the solar to the house terminal on the 1 2 Both switch?
I think that will be equivalent to connecting directly to the House battery. Will you have access to the fuse?
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Old 14-03-2018, 08:18   #6
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

Yes, that’s exactly what I’d like to do. The smaller fuse to protect the thinner wire going to the 12both switch will be on this wire, and yes there’s a place where it’s accessible. I also plan to fuse my batteries (as per discussion of Maine Sail on his site) using MRBF fuses which go directly on the pos battery terminal.
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Old 14-03-2018, 10:12   #7
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

You can tolerate some voltage drop from panels to controller. Panels will put out nearly same current up to 16V to overcome some drop. But it is most important to minimize voltage drop controller to batteries by using appropriate wire sizes for the length. IMHO you want the only direct connection to batteries to be the main switch. Small current you get from panels will cause negligible drop across switch and any fuses.
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Old 14-03-2018, 11:48   #8
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

A proper solar installation has the positive from the panels running into a breaker. The output of the breaker feeds the solar controller input. The output of the solar controller goes to another breaker. The output of that breaker feeds the batteries, either through a OFF-1-2 switch, or directly, your choice. You need to be able to disconnect the batteries from the solar charger and the panels from the solar charger independently as recommended by most charger manufactures. Having said that, check the installation instructions for your particular charger and follow their advice.
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Old 15-03-2018, 06:52   #9
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

Depending on the proper amperage capacity of the wires, I use only a fuse at the battery. In this case there would be a fuse at the switch as well. I do fuse each panel in my parallel arrangement.
I use a Blue Sea STDP battery switch to disconnect both the battery and panel sides of the controller.
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Old 15-03-2018, 08:15   #10
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Re: Connecting Solar Controller: Wiring All The Way To The Battery?

Once installation is complete, you will occasionally need to disconnect your batteries from your solar charger, such as when changing batteries, cleaning battery connections, etc. You may also need to disconnect your solar array to replace a damaged panel, add panels, etc. (caution, solar arrays can output lethal, heart stopping DC voltages!) To disconnect the system, you need a switch (I use breakers) to disconnect the batteries from the solar charger. Although not absolutely necessary, ideally this switch only disconnects the solar charger without disconnecting your batteries from other loads like your DC lights, pumps, electronics, etc. You also need a separate switch to disconnect the solar array from the solar charger. Because the output voltage of the solar array varies based on panel design as well as whether the panels are wired in parallel, series or a combination of both, the electronics of most solar chargers are powered by the batteries rather than by the solar array. This means the battery switch should be switched on first to power up the charger before turning on (connecting) the solar array. Conversely, the solar array should be switched off (disconnected) before disconnecting the batteries. Depending on the design of the charger, doing it the other way around can sometimes damage the electronics. Just to make sure I don't forget this, I have a label on my battery disconnect breaker that says, "First ON, Last OFF".
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