3 x 100w Solar Panels - Cable and T-Plug thoughts please

[Ian-n-Suzy]

Hi,

I'm just looking at ordering some bits for a 3 x 100w Mono Solar Panel system upgrade to our Van, wired in Parallel.

I was going to wire the 3 panels in parallel using a triple MC4 T-Plug near to the roof entry gland.

There would be a shortish run of about 1.5m from the tails of panels 1 and 2, to the MC4 T-Plug, and the 3rd panel already has an .8m tail which would reach the MC4 T-Plug.

With a run through the roof gland, to a Victron 100/20 MPPT of about 3.5m.

I considered wiring it in series to keep the amps down and let the MPPT Controller take care of sorting it out at the other end, but was concerned about shading on any part of the panels shutting the whole system down.

My question is regarding the cable thickness, I was originally going to go with 6mm2 Solar PV Cable, but if the pre-wired tails on the Solar Panels are 4mm2 will this have an impact?

Do you think 4mm2 be suffice considering the overall run of about 5m? (I'm unsure if the rules of voltage drop wiring sizes are the same for PV cable as even 4mm2 is pretty thick (rated at 55a - the 6mm2 is rated at 79a).

Any thoughts re cable thickness and the use of the triple F Plugs rather than Y Tails?

TIA

 

[Ian-n-Suzy]

No thoughts re using 4mm2 or 6mm2 PV Cable?

 

[Camping Gaza]

4mm would be fine all round, but bigger is better, whats the issue? even at 19 volts or there abouts DC, 5 meters of cable is nothing you will not get much amperage out of the panels even in full sun, certainly not close to 55 amps. But lessening the resistance all round is always a winner.

Not a lot in it really 4mm vs 6mm ? Use whatever you have the most of.

Run them in parallel cos in series in the slightest of shade will reduce the efficiency regardless of your controller. (google it for conformation)

Finally don't expect to get the performance what the specs tell you or you will be heartbroken.

If you can get all the connectors off the roof and into the van, and then it dont matter how you connect them ( I have mine connected using chock blocks) theres no water present

 

[TinaLes]

I discovered when I eventually found them,that the Solar pre-installed solar cables in our van were really good quality 6mm double insulated.
The problem was that my Victron Blue Solar Bluetooth controller has 4mm terminals, so it was a struggle to get them to fit. I had to buy a bag straight crimp pins in the end, which was annoying as I only need 4!
The cable run length from the roof gland to the controller would have been 5Mtrs approx, so 6mm was appropriate for 200watts of solar potentially delivering 16.67 amps, volt drop would vary as voltage increases/decreases from solar, but working on 12 VDC it was 0.47Volts representing 3.92% for the 5mtr run.

300watts of solar has a theoretical but not achievable (100% Full Sun) of supplying 25Amps.
Over a 5Mtr run with 6mm cable at 12VDC that would be a 0.71 volt drop representing 5.92%.
If you can fit 4mm cables between panels, then 6mm from below the roof gland position to the controller that would be best for volt drop purposes, however most vans are wired with 4mm all the way, but then they dont have 300 watt worth of panels fitted at the factory, as 100 watts are the normal option.
Good luck, check out the input/output terminal cable size on the controller beforehand if you can.

Les

 

[Camping Gaza]

Try gold plating your connections, you will have something to talk up about at sherry parties

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[Ian-n-Suzy]

Thanks for the replies.

I've fitted them before to previous vans and to friends vans also, and also to a couple of PV conversions, but was unsure regarding the 4mm2 or 6mm2, as I have usually gone "belt and braces" with 6mm2 PV Cable even replacing it at the junction box on the panels if it was fitted with 4mm2.

There is already a panel up there (going to ditch this and replace with 3 identical 100w panels), but the reg is only 6a and the wiring gauge didn't take into account any future upgrading. I'm just wanting to make sure I get the most out of it without going OTT if possible.

from Victron: "Max. cable size that fits terminals: 6mm² "

I'll hold back on the Gold plating for now though, lol.

Thanks again.

 

[Silver-Fox]

Can you not get two 150 panels on?

I recent renewed mine and joined two panels with the supplied 4mm then went to 6mm to controller.

I also shortened the 4mm cables instead of having coils on the roof ?

 

[Lenny HB]

No thoughts re using 4mm2 or 6mm2 PV Cable?

4mm will be fine. In summer when you have the highest output the small volt drop that will reduce your charge rate is not worth worrying about. In winter with the panels only producing a few amps the drop again will be insignificant.
e.g. if you lose 5% of 18 amps you will still have over 17 amps available, in winter if you lose 5% of 4 amps it only reduces to 3.8 amps.
Also the difference between 4mm & 6mm cable is only 2% over 5m so you are really only losing 2% compared to 6mm.

 

[Ian-n-Suzy]

Can you not get two 150 panels on?

Hi,

There is an Air Con Unit, Oyster, 2 big Heki's and 2 small ones plus a Turbo Vent already up there and they have been spaced awkwardly. So even going for 100w panels took some planning and I needed to find some "compact" panels to fit within the available space.