Branch Connectors or Bus Bars or Combiner

[Phil_413]

Hi, I'm new here and I'm trying to build an emergency solar and battery backup system. Where I'm having trouble is fusing my solar array setup. I have 4 Trina Solar panels, model number TSM-360DE06X.05(II) with the following specs:

Pmax = 360W
Vmp = 37.0V
Imp = 9.74A
Voc = 44.8V
Isc = 10.3A
Max Fuse = 20A

I want to use these panels in a 2S2P configuration since I bought a Victron 100/50 controller. If my math is correct, I get the following:

Pmax = 1,440W
Vmp = 74.0V
Imp = 19.48A
Voc = 89.6V
Isc = 20.6A

I attached a crude schematic. Feel free to critique the design and math.

But I'm trying to figure out where to build in fuses from the solar panels to the charge controller. I think I need 20A fuses on each of the two strings. But when I put these in parallel, what do I do? If I apply a 1.56 safety factor, I have 20.6A * 1.56 = 32.136. Many of the Y branches I've found are rated for 20A. Even the 4 input, 1 output branch is rated at 30A. So I think that's a no-go and I don't feel comfortable with a branch (but I could be wrong). I've seen recommendations for a combiner, but that seems a bit more complicated and cumbersome than I'd like. So, I'm wondering, is it safe to run both strings at 50 feet to bus bars and then fuse it between the bus bars and the charge controller? Is this safe this way? What recommendations do you have? I want this to be as safe as possible. I appreciate it!

 

[time2roll]

But I'm trying to figure out where to build in fuses from the solar panels to the charge controller.

No fuse needed. Can short the panels all day long and the wire will not get warm. No damage to the panels either.
Branch fuses are not needed unless three or more strings in parallel.

Even after the solar controller the amps are limited by the solar and with proper wire no fuse needed at the solar output.
Just a fuse at the battery or bus to protect the wire from the battery to controller.

 

[Phil_413]

No fuse needed. Can short the panels all day long and the wire will not get warm. No damage to the panels either.
Branch fuses are not needed unless three or more strings in parallel.

Even after the solar controller the amps are limited by the solar and with proper wire no fuse needed at the solar output.
Just a fuse at the battery or bus to protect the wire from the battery to controller.

I appreciate your input. Thanks!

 

[Phil_413]

I have a follow-up question regarding my design. Is there any reason that I shouldn't run two 10 AWG cables from my 2S2P configuration into bus bars (which will be in my garage)? I don't see that the current on each string will be an issue. I just wanted to avoid a combiner box since the total current (with safety factor) exceeds the amperage ratings on Y or Branch connectors. I appreciate your input. Thanks!

 

[time2roll]

That bus would essentially be the combiner box. I don't see any issues of concern.

 

[Phil_413]

That bus would essentially be the combiner box. I don't see any issues of concern.

Great, that I was my thinking. Much appreciated!