Solar confusion

[jonathanhsm]

To take advantage of all this glorious sunshine I am fitting a 100 watt panel to a 10 amp MPPT (dual battery) solar controller, and onto batteries, in a 12 volt system.The instructions say to use 12 awg 4mm² two core cable throughout.

I can understand that between the solar panel and the controller. – load surges exposed to the weather etc. But why can’t I use ‘normal ’ cheaper 2.5mm² 2 core cable inside the boat between the controller and the batteries which is rated at 25 amps ? Even 1.5mm² is rated at 15 – 20 amps.

 

[starfire]

Voltage drop....

 

[PaulRainbow]

To take advantage of all this glorious sunshine I am fitting a 100 watt panel to a 10 amp MPPT (dual battery) solar controller, and onto batteries, in a 12 volt system.The instructions say to use 12 awg 4mm² two core cable throughout.

I can understand that between the solar panel and the controller. – load surges exposed to the weather etc. But why can’t I use ‘normal ’ cheaper 2.5mm² 2 core cable inside the boat between the controller and the batteries which is rated at 25 amps ? Even 1.5mm² is rated at 15 – 20 amps.

Post #2 is technically correct, but it does depend on where you mount the controller, in terms of distance to the batteries.

How far is it ?

 

[wonkywinch]

Domestic 1.5 and 2.5 cable is usually solid core. Unsuitable for a vibrating location. It's why trains, planes & automobiles use stranded cable.

 

[rotrax]

If you buy the correct cable and connectors you will have reliability. Four years ago I installed 400W (2x200W panels). I kept wiring as recomended by the supplier, used proper terminals and connectors and kept the runs as short as possible. The connectors allow sealing with silicone grease, addition of a properly sized fuse and easy connect/disconnect.

Plenty of output, my batteries have never had any external charging since I installed Solar. When aboard in summer we run 2 large friges and a freezer 24/7.

 

[jonathanhsm]

Post #2 is technically correct, but it does depend on where you mount the controller, in terms of distance to the batteries.

How far is it ?

Its only about a metre. I am guessing I could use some 2.5mm² stranded cable as for a car/boat. But for the extra couple of quid and peace of mind I might as well stick with 4mm² !
Many thanks all.
Apart from vibration etc. I still don't quite understand how normal house 13 amp supply only needs 1.25² mm and a 10 amp supply on a boat needs 4mm² ?

 

[noelex]

Its only about a metre. I am guessing I could use some 2.5mm² stranded cable as for a car/boat.

2.5 square millimetre cable would be fine.

 

[Boathook]

Its only about a metre. I am guessing I could use some 2.5mm² stranded cable as for a car/boat. But for the extra couple of quid and peace of mind I might as well stick with 4mm² !
Many thanks all.
Apart from vibration etc. I still don't quite understand how normal house 13 amp supply only needs 1.25² mm and a 10 amp supply on a boat needs 4mm² ?

Home is 240V and boat 12V. You can have a bigger voltage drop at home. Voltage drop on a boat means less power, etc. 10% voltage drop on a boat is 1.2V so then down to 10.8 volts. A lot of boat electronics pack up just over 10 volts due to low voltage ......

 

[wonkywinch]

Its only about a metre. I am guessing I could use some 2.5mm² stranded cable as for a car/boat. But for the extra couple of quid and peace of mind I might as well stick with 4mm² !
Many thanks all.
Apart from vibration etc. I still don't quite understand how normal house 13 amp supply only needs 1.25² mm and a 10 amp supply on a boat needs 4mm² ?

The lower the voltage, the more losses per ohm of resistance.

That's why electricity distribution is done at thousands of volts and stepped down locally.

 

[PaulRainbow]

Its only about a metre. I am guessing I could use some 2.5mm² stranded cable as for a car/boat. But for the extra couple of quid and peace of mind I might as well stick with 4mm² !
Many thanks all.
Apart from vibration etc. I still don't quite understand how normal house 13 amp supply only needs 1.25² mm and a 10 amp supply on a boat needs 4mm² ?

13A ring main is 2.5mm.

If the controller is fitted 1m from the batteries you can use stranded 2.5mm cable, the voltage drop will be tiny. But, the difference between 2.5mm and 4mm is left that £20 per metre and as you're already buying 4mm to go from the panel to the controller it seems pointless using 2.5mm

2.5mm domestic cable is about 70p per metre cheaper, so an even bigger waste of time (and the wrong stuff)