Bigger cable for MC4 connector?

[smac999]

sounds like you are trying to combine all 6 panels to a single bigger cable? to a single controller?

your 3 sets of panels should each run to their own MPPT. so 10awg is likely fine for each one.

[GTom]

Originally Posted by CharlieJ

What is the output voltage of each of your series panels? What is the output current of each of your series panels and the current downstream of the combining wye.? And, finally, what is the circuit length from panels to the batteries, broken down into the series portion and the parallel section?

Just done the exercise. They are producing around 18V, I plan 2 series 2 parallel setup, meaning in the main cable that runs from the deck to the controller gets 36V and ~10A. In the future, adding more panels maybe 20A. According to this table, Voltage drop on a 6mm2 (10 AWG), 6m (20') cable should be around 3% for 10A load and ~2x as much for 20A load:


I can live with 3%, but would prefer to stay with that if I add panels my system.

Originally Posted by sailormed

I soldered 10mm2 cable in MC4 connectors. It can be done, is a bit bulky but works. I did it for the same reason as you. Was not really necessary but if it is possible, why not. The other solution of course is to just cut off the connector and do a watertight crimp with heated glue.

Perfect, thanks for the positive feedback!

Originally Posted by smac999

sounds like you are trying to combine all 6 panels to a single bigger cable? to a single controller?

Yes, I already have the controller, planned to go with one single large panel but found a package of smaller ones as a very good deal after the controller arrived. What's wrong with a 2s/2p setup when the parallel groups have a blocking diode?

[TheThunderbird]

13,00V
Do you think 3% drop is acceptable ? You have 12,61V..critical, almost inadequate to charge batteries.

And amperage Demanded for same wattage goes up by the squared value, say +7%.

I work on a 1% drop assumption, say 0,1V drop.

Mind to DOUBLE THE LINEAR LEN GTH

I use dorades to reach the below deck

[GTom]

Originally Posted by TheThunderbird

13,00V
Do you think 3% drop is acceptable ? You have 12,61V..critical, almost inadequate to charge batteries.
And amperage Demanded for same wattage goes up by the squared value, say +7%.
I work on a 1% drop assumption, say 0,1V drop.
Mind to DOUBLE THE LINEAR LEN GTH
I use dorades to reach the below deck

Interesting point, fortunately I don't expect from <15V from these panels, but weather will tell. The two Schottky also introduce around 0.3V loss - actually an argument for a proper combiner box is an ideal diode circuit (sells <10$ on ebay). However, in case it requires one single additional contact might just invalidate the ideal diode idea because of contact losses.

[noelex 77]

Originally Posted by GTom

I think that table is for 12v. If you are connecting two “12v” panels in series, in percentage terms the voltage and power loss prior to the controller will be less. You are better calculating this using the correct numbers, but as rough guide the 10% column would be about 4% at your voltage and the 3% column about 1%.

So, you are doing better than you thought .

[john61ct]

Use Circuit Wizard app to calculate

[smac999]

at 36volt, the % drop would be a 1/3.

10a at 12v 40' 8awg for 3%
10a at 36v 40' 12awg for 3%. 8awg for 1%

it's the same volt drop vaule. 0.xx v but it's 0.xx /36 instead of 0.xx /12

[NotCook]

Originally Posted by GTom

Interesting point, fortunately I don't expect from <15V from these panels, but weather will tell. The two Schottky also introduce around 0.3V loss - actually an argument for a proper combiner box is an ideal diode circuit (sells <10$ on ebay). However, in case it requires one single additional contact might just invalidate the ideal diode idea because of contact losses.

I did this, too, but just to join all my panels in parallel to then run by #6 to below decks to the controller and batteries. The junction box is in the lazarette. I used 8/2 Marine cable from the junction box to each panel. The 8/2 worked with the MC4 connectors, with maybe a few strands clipped to fit it in very snugly. Seeing up to 19.2 Amps on occasion from 423 Watts from 4 panels. Very happy with the arrangement.