PV System wiring help

[williamt]

Hello Everyone

This is my first post here, but I've been reading and learning from the forum for a while now.

Anyways, I'm in the process of setting up my PV system and I've reached a point of confusion and need some help please.  At my cabin I have 4-0 (0000) wires from my battery cabinet feeding to my electrical closet where the inverter will sit. From the batteries, once in the closet, I have a large junction box containing a 250amp fuse, after the fuse (on the load side) I tap off #2 wires to feed a 12v subpanel, then the 4-0 wire will continue to a breaker and the inverter. 
My problem is that i am going to use a Xantrex C series charge controller and I am confused on where to wire it into the batteries. Do I tie it into the 4-0 wires before the fuse (supply side), after the fuse (load side), or do I need to wire the charge controller directly to the battery bank? If I tie into the 4-0 wires is there a problem of feeding power to the sub panel and inverter when it should be feeding the batteries?

I've studied alot of wiring diagrams and even spoke to my electrician at work and i just can't seem to get clarity on this.  Please help.

Thank you, thank you, thank you

Will

[MountainDon]

Hi Will,

I have to work this AM     but shall be back in the afternoon and give you my thoughts.

Have you read our Off Grid Topic in the General Forum?

Don

[williamt]

Hi Don

Yeah I've red through the off grid topic a couple times, its been helpful, but i'm still confused on this point.
Maybe i'm just thinking about it too hard?
I look forward to your input

Thanks

[MountainDon]

I believe it is best to treat the charge controller and the inverter as totally separate circuits. So the charge controller should be connected to the batteries with its own cables and a fuse or breaker in the positive lead.

The NEC wants devices connected in a manner that will allow removal of one component without interfering with any other unit. That is one reason why I set my system up the way it is, using copper buss bars at the batteries. There is a positive, negative and a ground buss. The negative buss and the ground buss are connected together at one point. Only one point.Then the ground buss is connected to the 8 ft ground rod in the earth itself.

The batteries connect to the buss as a unit or several series strings using the buss as the parallel connection. The inverter also connects via the buss and has its own breaker. Ditto the charge controller. Any part can be removed for service without interrupting any other including not interrupting the ground.


Just as an aside, in case you were not certain, most AC breakers can not be used for DC. DC is different. A DC breaker should have a voltage rating that is at least the system voltage x 1.56 to ensure its ability to survive voltage spikes that can occur under certain cold weather conditions. This is for any DC system that is connected to PV modules.  Breakers may have a correct orientation for safe operation. Usually that means mounting the breaker vertically with the breaker arm located in the up position when ON or in service, not mounted on it's back. There may be variations, ones that are okay in other positions.

Some charge controllers need to be isolated, disconnected, from the batteries when being placed into service. Mine has to be first connected to the batteries and then when programmed connected to the PV modules. I don;t know about your model. I mention this as if there is a properly sized breakers between the PV modules and charge controller and another breaker between the charge contrioller and the batteries it makes that easier. The breakers also provide protection.

[williamt]

Thanx Don

Very informative.
So to summarize I can connect the positive from the charge controller to the positive of the battery bank with a breaker/fuse and the negative can tie into the negative bus in my 12v sub panel?

I have already connected the negative from my sub panel to the building ground

I was looking at Airpax breakers for the charge controller and inverter ( i believe i got this from your thread)
Whats your thoughts on the Square D QO line for lower amps, this is what i used for the subpanel as i read on different sites that they are UL approved to 48v DC?

[MountainDon]

The negative from the CC should be as direct as possible to the batteries. If that buss is close and there is no way the circuit can be broken when servicing another system component that would work.

The QO breakers are good for low voltage DC. Rated at 48 volts DC they should not be used in a system with a higher than 24 VDC nominal voltage, because of the safety factor that should be used. I have a couple in use; one each at 12 VDC and 24 VDC.

And yes, I do have some Airpax high voltage DC, medium amperage at the charge controller and high amperage (on the inverter)

If you have batteries in a series/parallel connection pattern there are better and best ways to connect them. Best is connecting any series strings to a heavy buss. How many batteries have you, voltage of each battery and system voltage?

[williamt]

since my system is still under construction I am using a lone marine deep cycle for 12V DC power when the generator is not on. I get 2 or 3 days at the cabin every two weeks so i'm trying to build in stages.  I am still shopping what betteries would be the best.

I have tested what the cabin in drawing off the generator and it is at 2.5 to 3 amps with everything on.