Solar panel wiring

[TyroSailor]

Evening all

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?

[stevejavelin]

The link below should take you to what you need. I've always found these products to be of good quality. Those connectors are pretty good and the wire is really excellent, Looks to be tinned.


http://www.lensunsolar.com/Solar-accessories

[TyroSailor]

Hmm - yes, thanks. But they seem to sell the connectors in groups of at least five pairs, and I only want one. And the 'food' miles in getting them from across the pond puts me off....
I found this place, https://www.ebay.co.uk/usr/friendly-green-giant selling on ebay. Only £1.69 a pair, British, and green

[Fulmar433]

I fitted a 60W solar panel to the roof of our off grid Coastal holiday home and used MC4 connectors and cables from eBay. I can't remember what size cable I bought, probably 4mm. Whilst not getting a direct soaking of sea water they get their fair share of sea spray and have worked faultlessly for the past 4 or 5 years. The cable lays on the roof and is showing no signs of sun damage. One problem seems to be with the battery, it seems to have lost its full capacity prematurely. The solar regulator is showing the battery is fully charged, but the capacity seems a lot less than it was. I have recently bought a Cetek 7 amp battery charger and have the battery at home currently running a reconditioning programme trying to improve it. I think I should have brought the battery home for some mains charging, a bit more regularly, rather than just relying on the solar panel. Maybe regular charging with the boat alternator will avoid this.

[Nigel Birch]

This sort of thing you mean?

https://www.edwardes.co.uk/en/products/ ... rPEALw_wcB

[stevejavelin]

Hi Steve

Look at the link again, 4th item. Also although for some reason price is given in dollars, they have a UK warehouse and supply from there. It all comes from China initially, like most things.

Don't know why I'm so keen on this firm other than they've been cheap for years- I bought my first panel off them about 10 years ago. My latest 60W semiflex seems really good but the wire and connectors are superb.

Enjoy whatever you get. You just can't beat the magic of solar

[BarryandLinda]

Hello Steve, I'd be really interested in your experience with your new solar panel and it's wiring. We had a 60w panel for about 10 years that expired 3years ago. We want to buy another, and will probably go for a 100w semi flexible which we don't want to mount permanently but move around as necessary to get the best output. We have an MPPT controller that is rated to 100 amps with the wiring going to a 2 pin deck plug on the stern. It's 3 core wire with the neutral wire unattached. Looking at the new connectors on various websites it seems my old plug is no longer fit for purpose. My questions are how can I make use of the deck hole to attach the new plug ( or is it plugs), and what has been your experience so far, or will I have to rip out the old cable and start again.
Comments from anyone with experience of the new panels would be welcome.
Many thanks.
Barry

[TyroSailor]

Hello Barry - and Linda

I'm heading for the boat in the next day or two and so will be able to report on the condition of the panel, its connections and the battery it's been charging (I hope) over the winter.

My 50W "semi-flexible" is mounted on a sheet of varnished marine ply in which I cut a hole for a handle and in the corners for lashing it to the south-facing rail. I shall unlash it when I start sailing and move it around as required. The MC4 connectors looked pretty robust, but as they were going to be unattended over the winter I put a layer or two of self-amalgamating tape over them to be on the safe side.

I doubt if the type of deck plug matters much, as long as it's watertight and makes good connections. No reason why the old one shouldn't continue to work, as long as it's not too corroded or can be cleaned up. Do have a look at it though - salt-laden air and spray can wick down the wires and corrode it from the inside with no external signs. I haven't yet fitted a deck plug - that's one of my jobs for this season - but at the moment I simply have the flex running in through a little gap in the companionway (and the cable from a 5W panel trickle-charging the engine battery comes in on the other side). To the inboard end of the flex I've fixed a socket such as is found on a lawn-mower flex, and run a short length to the regulator (Solsum 10A) with a plug on it. This will enable me easily to disconnect the whole thing if required.

Maybe I should have used three-core flex neglecting the earth conductor - inelegant but effective.

[BarryandLinda]

Hello Steve,
Just read your post on another thread and your panels seem to be doing exactly what you want them to. Thanks for the update.
Regards
Barry (and Linda)