Best Way to Join Two 8S Packs With Two 8S BMS's

[guidecca]

Your output breaker should be 20% over your expected load (63A) to prevent nuisance tripping. 75A or 80A?

The output breaker is 63A. Not sure what the output load is. The SCC has a maximum PV input current of 40A. 32.07A is the combined short circuit current of these three solar panels. So, the array is not over-amped. I am still concerned about the 32.07A frying the 12awg solar wires. I don't know if they are isolated or not. All the positives wires are on the same busbar and all the negative wires are on a different busbar. They go into the SCC; I don't know if there is a circuit until they get to the breaker and the SCC. * Correction: 25A vice 25v *

 

[MisterSandals]

The output breaker is 63A. Not sure what the output load is. The SCC has a maximum PV input current of 40A. 32.07A is the combined short circuit current of these three solar

Ok, disregard that comment. I will try to clean up that post.

 

[guidecca]

If the solar panel wires to my three panels is 12 awg with an ampacity of only 25 amps AND I have all three panels in parallel AND they have a combined short circuit current of 32.07A. How do I isolate the solar panel wires from the 32.07A?

First, 20A inline MC4 fuses are attached to the 12awg solar panel positive wires. Then, all the wires are inserted into a homemade junction box with two busbars; the positive wires go to a positive busbar and the negative wires to a negative busbar. Lastly, 6 AWG wires (positive and negative) exit the junction box and connects to a 63A DC breaker inside my van and then the 6 AWG wires go to the solar charger controller.
Are the solar panel wires protected? * Correction on drawing: change 25v to 25A *

ADVICE WELCOME

 

[Hedges]

20A Fuse per string protects the wires from 37A. (except for short run from combiner box to fuse)

 

[guidecca]

The current only increase to 32.07A when the three panels are connected together in this parallel config. We know that 12 awg wires will fry. What if the short run from combiner box to 20A fuse were 10 awg wire or 8awg wire? 8 awg wire would carry the current to the busbars without an over current issue. The only question I have is can you join two different size solar panel wires with a fuse between them?

 

[Hedges]

Dc mini breaker confusion

Wires in PV rack could short due to pinching or rodents. Pigtails between plastic combiner box and MC fuse holders not as likely, consider what is around them. Often, combiner box has fuse holders or breakers inside. Can a pigtail from a 12 awg solar panel wire to an inline MC4 fuse and...

diysolarforum.com

 

[guidecca]

View attachment 121514

View attachment 121515

Steve,

This is a diagram from Overkill BMS. Can you connect positive output on one BMS to negative output on another BMS? See the attached diagram.

 

[Steve_S]

Steve,

This is a diagram from Overkill BMS. Can you connect positive output on one BMS to negative output on another BMS? See the attached diagram.

Of course I often misinform & misdirect folks as I haven't got any sort of clue about anything... Yawnnnnn

 

[guidecca]

I don't know either. Hope the fires up there are getting rained on.