question

andrer avatar image
andrer asked

Reducing Amp's for 30A MC4 current limit by using Y cable?

Hi,

Can anybody tell me, if this makes any sense?
Therefore, using a Y cable to reduce the Amps per MC4 port.

The thing is, I like to avoid 4 cables going from the roof to the basement. 2 Cables (6mm2) are already there. But coming with over 55Ams, I have to reduce the Amps.

I have a MPPT 150/100 installed already in the basement

bildschirmfoto-vom-2023-12-28-02-22-25.png

The whole panel configuration here:

Panel configuration

mppt_calculator_28.12.2023, 02_30_07.pdf


And because the max Amps can be even higher than 55A, I even like to split one cable into 3 cables as I have 3 ports anyways.

Thanks and br

MPPT Controllerswiring
bildschirmfoto-vom-2023-12-28-02-22-25.png (880.0 KiB)
mppt-calculator-28122023-02-30-07.pdf (706.8 KiB)
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3 Answers
klim8skeptic avatar image
klim8skeptic answered ·

@AndreR As you know a MC4 connector has a 30a current limit. Including the ones on your Y splitters. You better run 2 pairs of cables from your array, with 2 strings on each pair.

Dont forget to have series fuses on each string of panels, both on the + and - cables.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
Another option would be to split the output between a PV breaker and the mppt. 2 cables into breaker, 4 (or 6) cables out.
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Alexandra avatar image Alexandra ♦ commented ·

You could terminal block them, run one fat cable down.

Terminal block and split up the cable over the MC4s again.

Just need to pay attention to lengths so you get a good sharing over them.

They are all common.

Example (not the best one but something like that will work. Just be aware of quality). You can mount it in an ip65 box with glands. Check the UV rating of the box/glands first though if mounted in the sun

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kevgermany avatar image kevgermany ♦♦ commented ·
Agree, but this doesn't solve the problem at the MPPT.
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andrer avatar image andrer commented ·
Oh, right, didnt think about that the MC4's have that limit too! The breaker seems to be the solution then! Thank you so much!!!
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kevgermany avatar image
kevgermany answered ·

Thinking more about this.

You have 4 strings. Configure as 2 pairs of 2 strings.

For each pair of two strings - use Y cable 2 into 1 into solar isolator - then from isolator into one set of mc4 connectors on the MPPT.

This keeps the current below the mc4 limit.

Don't forget the fuses as mentioned by @klim8skeptic

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Alexandra avatar image Alexandra ♦ commented ·
Two strings is still four wires (2neg 2 pos). Not sure if that was the four wires he didn't want. Or if four sets of wires.
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der-neue-hier avatar image
der-neue-hier answered ·

The MC4 conectors in the MPPT is bridged, so it doent matter if you are not over the 70A, there are also MC4 for 40 A to buy

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