Combiner Box

Arrow

I've got a relatively small, low power solar setup. In all, I'll have two or maybe three strings generating up to 400W. Do I need a combiner box for such a small arrangement? Or can I simply use 2 to 1 MC4 connectors? What's the limiting factor: The ampacity? The potential rat's nest? Something else?

Thanks

BB.

Re: Combiner Box

You need to look at the Series Fuse Rating for your solar panels...

For example, you may have a panel with Isc~8 amps, and a series fuse rating of 15 amps.

If you have a three parallel string array--If one panel is shorted, then the other two panels can backfeed ~16 amps into the one shorted panel/wiring harness.

Typically, you can have one (no parallel) string or two parallel strings, no combiner box/fusing is required. And if you have three or more parallel strings, then a fuse/breaker per string is required.

-Bill

Arrow

Re: Combiner Box

I see what you mean. All the combiner boxes I see online are way over spec'ed for my purposes -- 20 inputs rated to 1000V; that sort of thing. Is there a smaller, cheaper but still safe way to combine power from my various PV strings?

PV specs: STC/NOTC
Pmax 205W/148W
Vmp 37.7V/34.4V
Imp 5.43A/4.30A
Voc 45.3V/41.6V
Isc 5.81A/4.70A
Maximum series fuse rating 10A

vtmaps

Re: Combiner Box

Arrow wrote: »

I see what you mean. All the combiner boxes I see online are way over spec'ed for my purposes -- 20 inputs rated to 1000V; that sort of thing. Is there a smaller, cheaper but still safe way to combine power from my various PV strings?

I suggest: http://www.solar-electric.com/mnpv3.html

Its weatherproof so you can set it up outdoors near the panels. It has room for a Midnite surge protector. The best place for the lightning arrestor is outdoors by the panels... you don't want lightning coming into your house on the PV wires.

Are your panels on the roof? If so, run the ground cable down the outside of the house to its ground rod.

--vtMaps

Arrow

Re: Combiner Box

vtmaps wrote: »

I suggest: http://www.solar-electric.com/mnpv3.html

Its weatherproof so you can set it up outdoors near the panels. It has room for a Midnite surge protector. The best place for the lightning arrestor is outdoors by the panels... you don't want lightning coming into your house on the PV wires.

Are your panels on the roof? If so, run the ground cable down the outside of the house to its ground rod.

--vtMaps

They're on an outdoor pagoda in a school's courtyard. I'm planning on putting as many components as possible in a glass-roofed underground container, guts open if possible as an educational tool.

vtmaps

Re: Combiner Box

Arrow wrote: »

They're on an outdoor pagoda in a school's courtyard. I'm planning on putting as many components as possible in a glass-roofed underground container, guts open if possible as an educational tool.

All the more reason to do it right. The midnite solution is listed and meets code. If you are trying to educate students you should show them how to build a safe legal system.

--vtMaps

Photowhit

Re: Combiner Box

Since you'll be in a weather proof area, you could save a bit by using one of the Midnite Baby Boxes. You will also need din rail breakers for each string(up to 4 strings). You can combine the negative side of the solar panel feeds with a suggested Bus Bar, or you can now find push-in multi line wire connectors, note that these are connectors and must be done in an accessible manner, like inside the baby box.

ggunn

Re: Combiner Box

Arrow wrote: »

I've got a relatively small, low power solar setup. In all, I'll have two or maybe three strings generating up to 400W. Do I need a combiner box for such a small arrangement? Or can I simply use 2 to 1 MC4 connectors? What's the limiting factor: The ampacity? The potential rat's nest? Something else?

Thanks

You can use Y connectors if you only have two strings, Any more than that and you need a combiner box.

BB.

Re: Combiner Box

Be careful if below grade--You want to make sure that it does not get flooded in winter/from sprinklers.

-Bill