#153680  by NeilV
 Fri Aug 02, 2019 9:02 pm
Nut17 wrote:
Fri Aug 02, 2019 8:23 pm
It is often too easy to complicate things unnecessarily. A good result. :TU
You could simply fit an ignition switched relay between the battery banks so they are only in parallel when the engine is running.
Thanks, that’s basically what the DVSR does now, only connecting them when there’s a charge voltage high enough (27.6v for 2 minutes) ... think I just need a diode to stop the lithium’s higher voltage from holding the connection once it’s triggered, though the 50A cutoff works there too 🤔

The manufacturer has a “lithium” wiring diagram showing the ‘inching switch’ as this relay, but I tried this manually and the lithium having more than 26v (till 30% SoC) just keeps it connected anyway :roll:
 #153731  by NeilV
 Sun Aug 04, 2019 7:08 pm
Neddy wrote:
Sat Aug 03, 2019 10:05 pm
He means cable with a cross-sectional area of 50mm², Ray.
Yep, battery interconnect rated for 400A (leftover from my double AGM via DVSR setup before)

Then 16mm2 for the solar controller and bigger Inverter, and the connections between the 60A BMS (negative) and again on the 65A Victron battery protect (positive) complements of the autoelectrical brother in law :D
 #155719  by NeilV
 Sat Oct 12, 2019 11:38 am
So I’m soon to add my final 280W panel and have an end result of 2*250W(8A) and 2*280W(9A) for a total 1060W through my 40A Epever Tracer all at 24v.

Not really fussed at the small difference between the panels, but recently heard that MC4 plugs are only rated to 20A, and as I have all three (current) panels on a three way MC4 joiner before coming down through the roof on one pair of 6mm wires down to the controller, I’m a bit worried I might blow either the 20A inline fuse or overdo the 20A rating of the plugs.
I can easily up the fuse, but it’s there to protect the plug so not really a good idea!

Lithium will take whatever it can at max input so the potential 30-34A from the set all in parallel in good sun could be a problem?

I’ve already seen a 20A input via the solar once when I came out of a shady park into the good sunshine around 11am, so I’m now wondering how to safely accomodate the extra panel best!

I think I basically have two options, without another wire penetration to the controller (or extra controller)
1) to series and then parallel the two pairs 250-280=530W (twice) thus dropping the amp input and letting the MPPT sort it out inside (also potentially keeping the voltage higher for longer in low light)

2) disconnect one of the panels and only connect when it’s needed in low light/winter conditions

I’m heading toward (1) as it’s not a manual control so less likely to go wrong, but know that some here say parallel is best no matter what!

At this point I’m not able to do another hole in the roof as SWMBO is anal about the potential leak factor :lol:

Your thoughts?
 #155733  by Neddy
 Sun Oct 13, 2019 12:46 pm
No need to drill more holes, Neil - your existing 6mm cable would be quite adequate whichever way you go. Even with all 4 panels connected in parallel, transmission losses would be acceptably low at only 1.5% for a 3 meter run, for example. With mis-matched panels you are never going to get your full 1060 watts worth, but that won’t matter on sunny days when you will have an ample sufficiency of solar power regardless of whether you connect the individual panels in series or parallel. The situation would be very different in low light conditions, however, when running all four panels in parallel would give double the charge current of the series/parallel setup you propose. There are pros and cons whichever way you go, but for me, going all parallel would be the better option by far, giving more power when you need it the most.
MC4 connectors would be adequate – the chance of your seeing a solar panel output of more than 30 amps is very slim indeed. If you really are worried about this, don’t use an MC4 connector for the final 6mm panel/controller lead.

 #155737  by NeilV
 Sun Oct 13, 2019 5:11 pm
Thanks Neville,

Yeah it’s the 20A limit I’m worried about rather than 30A, but what junction box/connectors do you suggest for 4-1 liking on the roof? I currently have a 2-1 MC4 Y junction and a 3-1 junction too.

I was planning to junction the 2x280W at the back where they’ll be anyway, and then junction that pair with the other two with the 3-1 just before they go though the roof... but am open to a different connection system there if the MC4 are under spec?
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