Combiner box

Gregaba

I have a 400 watt system with a Renogy 40 amp cc and I also have a Epever 100 amp CC with 800 AH of battery's..

I receiver  my new 4 100 watt PV's this week. All running 12V for now.

I want to use the Epever for all 8 100W panels.

Planning to run one set of PV in series and one in parallel.

My question is I was looking at combiner box's today and noticed the breakers are listed between 10 and 68 amp's.

Which one should I order?

BB.

It depends on how you wire the array (typically panels all in parallel for a PWM controller on 12 volt battery bank; or series or series/parallel on MPPT controller and/or higher voltage battery banks).

You need to look at the solar panel specifications... Typically you will see a series protection fuse (or similar wording) rating. For example, a 100 Watt panel with Vmp~18 volts, the series protection fuse rating will be around:

• 100 Watts / 18 volts = 5.56 Amps Imp
• 5.56 Amps * 1.25 Isc (estimate) * 1.25 typical series fuse rating = 8.7 amps guess--Or approximating 8-10 amps Series fuse (guess), may be as high as 15 amps--Check the specifications

For example, random 100 Watt Renogy panel:
https://ca.renogy.com/renogy-100-watt-12-volt-monocrystalline-solar-panel-slim-design/-dp58-152108/

Normally, you only put series protection fuses/breakers in when you have 3 or more parallel strings of panels...

To configure your array... You need to know exactly which charge controller/battery bank voltage you have...

For example a typical Renogy 40 Amp MPPT controller has a maximum Voc-cold voltage of 100 Volts (at least one spec I saw)... More or less for very cold climates, Vmp-std should be around 2/3rd of Vpanel-max (allow for sub freezing weather) or 100vdc*2/3=66 Volts

If your 100 Watt panel is Vmp~20 volts, then 66 volts / 20 volts Vmp-std = 3.3 = 3 panels in series maximum (warmer climates, you can run higher Vmp-array voltage).

For the Epever, around 150 VDC max * 2/3 = 100 volts Vmp-std max (for cold weather). Or 100 volts / 20 Vmp-std per panel = 5 panels in series for this controller (again in very cold climates).

The suggested minimum/optimum Vmp-array voltage is ~2x Vbatt-charging voltage... 2x14.75 volts charging = Vmp-array-sted minimum optimum = 29.5 volts... Or 2x "20 volt Vmp for 2 panels in series as "optimum minimum array voltage" for either controller.

For the 40 amp (MPPT) controller, .looking at a 2series * 2 parallel array (no combiner box needed).

For the Epever 100 amp (MPPT?) controller with 8 panels... You can run either:

• 2 series * 4 parallel (need combiner box with 15 amp fuse/breaker)
• 4 series * 2 parallel (don't need a combiner box).

The 2s*4p is slightly more efficient, but costs more in wiring and combiner box+fuses/breakers. The 4s*2p is slightly less efficient (by 1% or so) but saves you a lot in wiring and combiner box costs.

Again, review the manuals. And check the Voc/Vmp/Imp/Ispf (series protection fuse rating) and the exact controller(s) you are using (MPPT/PWM, specifications). It can be a bit confusing the first time through--But specifications do make sense once you step through them a couple times.

If you wanted to get "closer" to Vpanel-max input voltage rating... You/we really need to go through the math to see how many panels you can put in series (i.e., cold climates, Voc-array rises; climates that are always warm to hot Voc-array falls).

-Bill

Gregaba

Bill

Thank you again. For some reason this is starting to make a little sense to me as I read more on it.

Greg