Need to disconnect one array from another and don't want to die

[ron_jeremy]

This 24V off-grid PV system pre-dates me by many years but I've finally got around to starting some upgrades.

Currently, there are 8 x 75W panels (2 strings of 4) feeding into a Xantrex 150V/60A SCC as shown here:

arrays.jpg

Here's a pic of the combiner box:

combiner-box.jpeg

I have 3 x 350W panels to replace the lower 4 x 75W panels and will feed them directly into my new Victron 150V/60A SCC.
The existing 4 x 75W panels in the upper string will stay connected to the Xantrex SCC until I get around to replacing those panels, too.

So, there will be two independent 3 x 350W strings feeding two 150V/60A SCC's.

Questions:

- What is the correct equipment disconnect sequence for me to safely disconnect the lower string?
- Once I've disconnected the lower string from the combiner box is it ok to leave the upper string of 4 x 75W panel's connections in the combiner box (I would remove the box once new panels are also installed on upper mount)?

[littleharbor2]

Wait till early evening or daybreak., or in the dark if you choose. There won't be any current flowing. Just remove one wire nut, pull the lower string out then replace with a yellow or red wire not, whichever fits best. Repeat with the other leg.
Leave the one string connected, no problem.

[ron_jeremy]

Should I be turning off any equipment: inverter, AC disconnect, DC disconnect, etc?

[littleharbor2]

If you have a disconnect between the PV and Controller you can disconnect there but if you do this at the times suggested there will be very little or no current flowing so I wouldn't worry about it. Your array is not large enough to be a problem. When you add the new panels you should have some sort of dc rated breaker/disconnect before the controller if you don't already.

[azdave]

Very secure base on those two pole mounts.

Good luck with the project!

[ron_jeremy]

As mentioned above, I'll be wiring 3 panels in series on each mount and feed each string to two independent 150V/60A charge controllers.

This is the spec of the existing panels I'll be removing:

panels-old.jpg

Specs of the new panels to be installed:

panels-new.jpeg

A few questions, if I may:

• The existing solar charge controller output wires go directly to the battery bank main positive and negative terminals. Do I simply follow this same procedure and add the output cables from the new SCC to the battery bank terminals, too?
• The wires from the existing SCC to the battery bank have "1000V 6 AWG" written on them. Can I use the same cable for the new SCC considering the much larger 3 x 350W panels in series connection?

[littleharbor2]

A few questions, if I may:

• The existing solar charge controller output wires go directly to the battery bank main positive and negative terminals. Do I simply follow this same procedure and add the output cables from the new SCC to the battery bank terminals, too?
• The wires from the existing SCC to the battery bank have "1000V 6 AWG" written on them. Can I use the same cable for the new SCC considering the much larger 3 x 350W panels in series connection?

You can go straight to the battery but you should add a set of bus bars to your system and connect your battery, loads and both SCC's to it.
How far away is the SCC and battery? What is the total current you will be sending on them? I notice you are planning on running two separate strings of 3 panels. 11 amps per string so far so good but are you going to pull another set of wires for the second string?

[ron_jeremy]

are you going to pull another set of wires for the second string?

Yeah, I have some cable for the other string. Speaking of cables, I need to get a couple more MC4 connectors because I forgot to factor the PV disconnect box. Anyway, while I wait for more MC4 connectors to arrive, can I use some large wire nuts to temporarily join the bare ends of PV cable in order to reach the SCC? The wire nuts would join one string of 3 x 350W panels to existing cable going to the SCC.

[littleharbor2]

Yeah, I have some cable for the other string. Speaking of cables, I need to get a couple more MC4 connectors because I forgot to factor the PV disconnect box. Anyway, while I wait for more MC4 connectors to arrive, can I use some large wire nuts to temporarily join the bare ends of PV cable in order to reach the SCC? The wire nuts would join one string of 3 x 350W panels to existing cable going to the SCC.

I believe I answered that question in another forum.