How to use the MC4 connectors on Smartsolar?

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Paul asked Mar 9, '20

How to use the MC4 connectors on Smartsolar?

Hi all,

The user manual for my smartsolar MC4 model does not help me in deciding which way to wire up my PV panels to the unit. I only have 2 panels (390 watts each) and was originally going to wire in series and then into the pos/neg in's on the regulator. However the MC4 model regulators have several pairs of MC4 inputs which means I could just send cables from each panel straight into the regulator without having to series or parallel them at the panels first.

So, what is the most efficient way to wire these panels up please.

A little more info in Victrons wiring ebook and regulator manuals would be a great help.

My panels are 390watt Voc 75.3v Isc 6.55A.

Thanks

MPPT Controllers Solar Panel wiring

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wkirby ♦♦ commented · Mar 09, 2020 at 07:19 AM

What is your battery Voltage?

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Answer 1 · 2020-03-09T07:42:41Z

Paul answered · Mar 09, 2020 at 07:42 AM

Battery bank is 12volt.

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Answer 2 · 2020-03-09T07:43:16Z

JohnC answered · Mar 09, 2020 at 07:43 AM

Hi @shars.p

Use this calculator: https://mppt.victronenergy.com/

That is a very high panel Voc, and unless you have a 250/ rated mppt you'll need to wire them in parallel anyway.

If just a 150/ unit, parallel should work fine anyway into any batt V. The MC4's run to a common bus, so it's just a convenience thing.

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Answer 3 · 2020-03-09T07:53:03Z

Paul answered · Mar 09, 2020 at 07:53 AM

I have just re-read the PWM vs MPPT whitepaper at Victron.com and if I read it correctly, PV panels should be wired in series to max voltage going in up to the limits of the regulator. The regulator then performs its P=VxA magic. This was my understanding originally and my plan was always to wire in series. I suppose what I am trying to understand is how the MC4 PV inputs behave ie are they going to series my PV inputs inside the unit if I just connect each panel to a pair of MC4's or are they just a parallel input? If parallel then I assume that the regulator will operate the most efficiently if I series the panels and then connect just as i would if I had a Tr version.

By the way my controller is a 250/80 MC4.

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JohnC ♦ commented · Mar 09, 2020 at 08:26 AM

In that case it won't matter which way you wire them. You're unlikely to see any difference in performance at all.

Choose by your wiring preferences..

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Answer 4 · 2020-03-09T08:20:47Z

wkirby answered · Mar 09, 2020 at 08:20 AM

JohnC is correct. With that combination oif panels and controller, you can pretty much wire them as you you like.
However, you are right, the controller will operate a bit more efficiently with the panels in parallel (Voc 75V), also this w configuration will help with any shading issues.

The MC4 connectors are all in parallel, so wire each panel to a pair of MC4 connectors to have the panels in parallel

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Answer 5 · 2022-12-07T02:34:43Z

missingegg answered · Dec 07, 2022 at 02:34 AM

My understanding is that it's a good idea to have over-current protection in place when paralleling more than two strings of panels. If a 3 input MPPT charger is just connecting the panels to a common bus, then hopefully the manual would instruct you on having appropriate external fusing?

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