
I have recently bought a Photonics 50W "semi-flexible" solar panel to keep the 100Ah domestic battery up to charge when I'm not on board, and to provide enough to drive autopilot, lights etc. when I am. It will operate through my existing 'Solsum' regulator. I'm about to mount it on a varnished marine ply board so I can lash it wherever is the sunniest but my problem concerns the wiring.
The panel has been supplied with a 0.9m length of single-core cable attached to each end of the diode box, terminating in MC4 connectors (apparently the standard for solar panels). Clearly this is not going to reach the regulator. I want to extend the cable to 5m or so in order to be able mount the thing more or less anywhere on the boat and have been told that I need 2.5 sq mm cable. This presents two problems:
(a) 2-core flexible cable of this size doesn't seem to exist. I've looked on line and it seems you can get 1.5 sq mm 2-core, 2.5 sq mm single or 3-core.
(b) this seems excessively large for the maximum 4A or so that the panel can produce. (50W/12v = 4.17A). In fact the output voltage is given as 17.5, so the max current will be 50/17.5 = 2.86A) So why do I need the chunky cable? Will 1.5 sq mm or even 0.75 sq mm do?
And are MC4 connectors really waterproof to IP67?