Combiner box...

[Nefariis]

Breakers should be bidirectional (certainly the ones pictured), there are no diodes in them to only cause the current to flow one way - in fact most of them are just a simple thermal trip.

I understand that no current will flow from the batteries back to the Panels, but that is because there are diodes in the charge controller and on the back of the PV panels - not because of the breakers.

And yes, my 4 panels will be installed in parallel and not in a series - 4 panels in parallel.


Ok, as I am writing this it finally hit me why this works...

Its simply just the definition between AC and DC current. DC only flows one way (from the power source) where as AC alternates forwards and backwards : /

I do quite a bit of AC wiring and I knew there was no way this would work as is - but I forgot that DC (unidirectional) doesn't quite work the same.

A good AC/DC practice model I suppose.

[ILFE]

Tomato Tomato.

There are still 3 breakers touching each other at one end like in the drawn (poorly) bitmap. Those breakers are not unidirectional - so what is stopping the current from two 15 amp breakers form tripping the third? Is the electrical current incapable of traveling backwards if there is a forward current? (which wouldn't make sense in that combiner box as it would seem like the two 15a breakers on the right would put a > 15 amp current on the breaker on the left)

Any more thoughts?

First, I am beginning to wonder if we are on the same page here. I may be off just a bit, but will do my best to stay with you.

Second, the DC current that passes through breakers in the combiner will only go one way, from the PV array to the controller. To my knowledge, no power will ever be sent back from the batteries, through the breakers and into to the modules. (If it were, it would drain the batteries at night time when no light were shining on the array. This is due to the protection diodes in the modules. I would hazard a guess that modern controllers have similar protection to prevent this from happening as well??)

Third, unless the panels are going to be installed in a parallel string, there is - realistically, no reason to even install a breaker between the PV array and the controller.

The only real purpose a breaker will serve, is as a switch to disconnect the PV array from the controller in order to work on modules in a series string. (If you have a two conductor wire that will carry more current than a single module can produce, the circuit protection will never be needed and the wire can never be damaged by the current coming from the PV array.)

When wiring two (or more) strings together in a combiner, will be the only reason / time to have breaker protection.

[Nefariis]

Tomato Tomato.

There are still 3 breakers touching each other at one end like in the drawn (poorly) bitmap. Those breakers are not unidirectional - so what is stopping the current from two 15 amp breakers form tripping the third? Is the electrical current incapable of traveling backwards if there is a forward current? (which wouldn't make sense in that combiner box as it would seem like the two 15a breakers on the right would put a > 15 amp current on the breaker on the left)

Any more thoughts?

[ILFE]

Am I missing something? How are people wiring these boxes so they input into a single slot on a charge controller?

Here is a typical combiner box and how it would be wired. Does viewing this image help?

midnite_combiner_box.jpg


EDIT: Alternatively, if it were possible to wire your array into a single series string, rather than parallel (as you have depicted in your drawing), you would only have one input to the charge controller and no need for a combiner box.

[Nefariis]

So I was looking through plans online for combiner boxes and the way these things are being wired from an electrical standpoint just doesnt make sense to me.


So if I built four panels that output 10 amps at 24v's and I wanted to put a 15 amp breaker on each panel - this is how I am seeing it done:

New Bitmap Image.png


This doesnt make any sense to me because fuses and breakers (most) are bi directional. So when the current passes through the first set of 15a breakers it could easily just feed back up the line and blow the breaker or fuse next to it.

Am I missing something? How are people wiring these boxes so they input into a single slot on a charge controller? It seems like there would have to be an isolator or a diode for each panel between the 15a fuse and the 50a fuse.

Thanks for the help