12v Cabling for Solar

rusty the athlete

I have a 100W solar panel connected to a 12v 60AH solar lead acid gel type battery and I want to run a 2 core (red and black) cable from the shed where the panel and battery are installed into the house where I intend to run five LED lamps (3 to 4watt, 12v) a couple of USB recharging sockets, and a 30W 12v fan in the summer. The distance is about 10m from the house to the shed. I'm confused about all the different cable sizes on offer, which are usually expressed in millimeter squared terms and often refer to auto applications rather than solar. Would anyone have an idea of what diameter 12v 2 core cable would be needed and what the amp specification should be for the cable? Thanks a mill.

2011

A 100W load at 12V means the current will be 100/12 = 8.33 amps

A 1.5mm sq. cable can easily carry a current of this magnitude, but the losses (due to volt drop) would be high. In order to reduce the volt drop a larger cable size can be selected.

To calculate the volt drop multiply total resistance of the cable by the current. A quick Google will provide you withe the resistance per meter of cable sizes. Now you just need to decide what losses are acceptable while considering that larger sized cables cost more.

Does this answer your question?

freddyuk

You are not looking for "solar" cable but low voltage (auto) cable. This is rated by amps so you need to total up your maximum amps for the loads you plan to use and multiply by 1.5. Amps = Watts/Volts. Then check using a calculator (google it) to check the voltage drop along 10 m.
So if you get 17-20 amp twin core cable it should be plenty but needs to be double insulated. You can use speaker cable but this is not double insulated normally.
Use a fuse at the battery end to protect the circuit.
A 100wp module is not going to give you very much power unless in full sun and certainly not in winter. I recommend more solar input unless you usage is intermittent.

rusty the athlete

Thanks guys, there is enough info to help me find the cabling I now need. Many thanks again. By the way Freddy, my 100W panel does well even in an Irish winter, Ive never had any problems and the solar controller indicates I am getting power and remaining fully charged even on the gloomiest of days. In my summer house elsewhere I run 7 led lights and two 30w fans off an 80W panel array via a 45AH battery and this seems fine although this is in Thailand where there is year around almost direct sunlight.

freddyuk

Great if you live within the watt hours available no problem. I don't know what you run off the USB etc. but a router etc. could use a bit of constant power.
I would not rely on solar controller to give you correct readings all the time unless it is a well made unit. Also it is best to mains charge such a battery regularly to give it a "full" charge as solar rarely does this thus reducing the lifetime of the battery.
Thailand is cheating! If only we had that direct sunlight ESB would be out of business. At least our days are getting longer now as we turned the corner.