Directional DC breakers in combiner

Re: Directional DC breakers in combiner

The "combined DC plus bus" is the source of the high current (not really that high for solar panels vs battery bank). The current direction "reverses" if one of the panel strings is shorted out... So as drawn, the configuration is correct (assuming LOAD is at the bottom of the breakers in this drawing).

Regarding your main array cable back to the charge controller--You do not need another breaker. The wiring should be rated to carry the total array current. (3x12amp=) 36 amp minimum rated cable.

For most installation, folks use larger cable to keep voltage drop down... So there is no chance the solar array will exceed the current capacity of the cable--There is no requirement an additional main breaker unless you want to install an "array off switch" next to your charge controller (for example, the combiner box is a fair walk away/top of roof/other difficult spot to reach).

Of course, there are breakers for every positive cable leaving the battery bank sized to the loads/cable awg size.

-Bill

Re: Directional DC breakers in combiner

unyalli wrote: »

The load would be the charge controller correct?

Think of a shorted solar panel or shorted charge controller as the "loads" (i.e., current flow is reversed--Source of high current is the PV bus bar or Battery Bank).

The MNEPV din rail breakers are positive at the bottom where the panels connect negative at the top where the bus bar is.

If I understand correctly, that would be "backwards" for a common installation that assumes battery/pv bus is the common "top" of the breaker. Not sure what is going on (unless these were designed for telecom system that have -48 volt power systems).

A shorted panel will pull current in reverse from the other panels through the breaker.

Yep--Under an "normal" conditions, it is not possible for a solar panel to exceed Isc "generated output" current (unless there are reflections from snow/mirrors/windows amplifying the solar irradiation).

-Bill