Breaker and or fuse sizing

Joe94

I am building my first PV set up for my off grid cabin. It is a weekend use cabin and I discussed sizing the system in another thread. My question now is how size my breakers and fuses. The set up is to run a 2x250 panels in series at 24v to a midnight classic 150. My battery bank will consist of 4 210ah golf cart batteries at 12v and then my inverter is a Suresine. I will also have a automatic transfer switch for my generator. The set up will need to meet code and has to be inspected. I called my local inspector and asked him a couple questions but he has never inspected a off grid PV system and told me to just draw a line diagram to submit with the permit and label everything clearly. So I'm working on drawing and planning this thing and have a few questions.

1. Should I use a combiner box for only 2 panels? My thought is no but I'm open to suggestions.

2. Should I use a breaker or fuse between the array and charge controller and size.

3. How should I set up the connections between the charge controller, battery bank, and inverter. In a panel of some sort or just run lines directly between things. I'm thinking in a panel but would like some advise. I want everything to be clean and organized but don't want it to be more costly or complicated then it needs to be.

I'm sure I'll have more questions at I get further in to this.

Thanks
Joe

Vic

Re: Breaker and or fuse sizing

Hi Joe

In the Classic manual, there are some wiring diagrams, and breaker size and cable size recommendations in the Appendix of that manual:

http://www.midnitesolar.com/pdfs/classicManual.pdf

You do not need individual breakers/fuses for the PVs, as you have a single string (at this time).

You should really have a breaker at the PV input to the Classic, and must have a breaker on the output of the Classic -- in the battery connection to the Classic. Use the manual info for sizing these breakers and the cables.

You will need a breaker in the positive connection between the inverter and the battery. More later, Good Luck, Vic

mtdoc

Re: Breaker and or fuse sizing

Breakers are sized to protect wiring. Wiring is sized to accomodate anticipated maximum current. If you think you might expand your system in the future (as many do) you might want to oversize your wiring into and out of the Classic CC now.

As Vic reccommends, you want a breaker into and out of your Classic. Midnites Baby Box combined with their DIN mount DC breakers is a nice economical solution for a small system.

Cariboocoot

Re: Breaker and or fuse sizing

You do not need any sort of circuit protection for just two panels.

Now here's the important question: are you going to stay with just two panels forever?

Think about future expansion, and wire for it now. That way later on you only have to plug in the panels and breakers and flip them on: all the right size wiring and connections will be there to handle the increased power. It sure beats having to take out all the old wiring and put in new.

Joe94

Re: Breaker and or fuse sizing

In the short term I will probably add 1 more panel at some point. 500wh is a little on the small side for the battery bank. Long term 3 to 5 years maybe I would like to make it a full time residence and I will be upgrading the system. I figure by that time my golf cart batteries will be getting a little week and I will take a look at upgrading the whole system. That is why I am going to use a midnight it should still work for future expansion as will the panels. I had already planned to use wire that will accommodate a larger array and battery wiring.