I have 9x 330w Japan Solar panels on the NE facing roof and 8x 330W panels on a NW facing roof. Max open circuit voltage (STC) for each panel is 46V and max power 8.7A.

My old/current inverter is an old mecer, that used 3x3Pv  and 2x4PV strings in parallel on a combiner box. And as I found out the inverter has only 1 MPPT and because the strings are on different roof angles but all on the same combiner box, the system doesn't work very well (yes, there are bad installers out there.)

I'm upgrading to a sunsynk 12k 3p and so I need to up the input voltage to the new inverter to make it compatible: My plan is to put the 9x NE  panels in series and connect to one MPPT and the other 8 xNW panels on one string in series going to the other MPPT. This will give me a voltage of around 400v on each string which is what the Sunsynk likes  (Input range 200-650V). Please tell me if I'm wrong here, so I don't blow my inverter up). The chase from PV's to inverter is about 16-20m.

I have  a number of questions relating to the wiring and isolaters and fuses/surge protectors:

1. What gage solar wire is minimum for this load and distance to go from PV to inverter? 4, 6, 10mm?
2. What else do I need to put between the PV panels and the inverter?

• Cut off switch/isolater ? One per string?
• A fuse? If any, at what rating? On pos and neg cables?
• A surge protector? We live in George, so there is not much lightning?

     3. If I can reuse some of the old cable, and I need to join pieces together, is it ok to use a high amp chocolate block connector, or solder a join plus tape/heat shrink, if the the joins are not exposed to the elements?

Welcome. 

Quotes/installs I've seen have used 6mm wire, and "16-20m" isn't a huge distance. I would imagine that a bit of voltage drop from a string is inconsequential versus say a 12V automotive system. 

I don't have a PV combiner box but simply protection/isolation (2 in 2 out), one string to each of the 2 MPPTs, with each + and - fuse protected, each string surge protected, and each string can be isolated. Picture below. 

Fuse rating - I think your string amp plus add 25% margin. Others better placed to answer. 

Reusing old cable - cable isn't too expensive, may be best to replace, and connection surely via solar connectors rather than blocks?

 

Edited March 14, 20232 yr by Kalahari Cruiser

3 minutes ago, Kalahari Cruiser said:

Welcome. 

Quotes/installs I've seen have used 6mm wire, and "16-20m" isn't a huge distance. I would imagine that a bit of voltage drop from a string is inconsequential versus say a 12V automotive system. 

I don't have a PV combiner box but simply protection/isolation (2 in 2 out), one string to each of the 2 MPPTs, with each + and - fuse protected, each string surge protected, and each string can be isolated. Picture below. 

Fuse rating - I think your string amp plus add 25% margin. Others better placed to answer. 

 

This is how a PV interface should be like. 👍

Thanks for the reply, I'm off to go shopping for Mr Z.J. Beny and friends. Wish me luck in finding someone with stock🙄

I had mine made up to spec by Advanced Product Technology (APT) in an IP65 rated housing. Received excellent service and good communications from a gentleman called Mitch (I think he’s in the Durban branch, had it sent to Cape Town branch from where I collected by courier). I felt that price was fair too. 
 

https://www.aptsaonline.co.za/pages/pv-combiner-boxes-600v-1000v-dc

On 2023/03/14 at 10:50 AM, Againstthegrains said:

I have 9x 330w Japan Solar panels on the NE facing roof and 8x 330W panels on a NW facing roof. Max open circuit voltage (STC) for each panel is 46V and max power 8.7A.

My old/current inverter is an old mecer, that used 3x3Pv  and 2x4PV strings in parallel on a combiner box. And as I found out the inverter has only 1 MPPT and because the strings are on different roof angles but all on the same combiner box, the system doesn't work very well (yes, there are bad installers out there.)

I'm upgrading to a sunsynk 12k 3p and so I need to up the input voltage to the new inverter to make it compatible: My plan is to put the 9x NE  panels in series and connect to one MPPT and the other 8 xNW panels on one string in series going to the other MPPT. This will give me a voltage of around 400v on each string which is what the Sunsynk likes  (Input range 200-650V). Please tell me if I'm wrong here, so I don't blow my inverter up). The chase from PV's to inverter is about 16-20m.

I have  a number of questions relating to the wiring and isolaters and fuses/surge protectors:

1. What gage solar wire is minimum for this load and distance to go from PV to inverter? 4, 6, 10mm?
2. What else do I need to put between the PV panels and the inverter?

• Cut off switch/isolater ? One per string?
• A fuse? If any, at what rating? On pos and neg cables?
• A surge protector? We live in George, so there is not much lightning?

     3. If I can reuse some of the old cable, and I need to join pieces together, is it ok to use a high amp chocolate block connector, or solder a join plus tape/heat shrink, if the the joins are not exposed to the elements?

On the cable size, the Sunsynk manual will tell you what size cable you should use for everything including grid connection and PV cable size. 4mm2 cable is usually more than enough, will see losses of less than 1% on the length you are going to use