Help Connecting A Solar Junction Box
January 24, 2010 10:31 PM   Subscribe

I purchased a junction box for solar panels off ebay and need help figuring out how to properly connect it to a 12v battery.

Here is a photo of the box:

The thick wires connect to my solar panel, but I don't know how to do the other end. There are fuses and then openings with exposed metal. Should I just solder solid 14 gauge wire to the metal? Just want to make sure I get it right. The ebay seller did not respond to my queries unfortunately. I appreciate the help!
posted by meta87 to Technology (15 answers total)
Can you point to the auction? I can't see any useful details in that picture..
posted by Chuckles at 10:47 PM on January 24, 2010

On second thought, are those just push terminals? Not great for the current they have to handle, if that's the case, but I guess it works..

Okay, here we go, looks to me like it is intended to mount straight on the back of a panel, like this.
posted by Chuckles at 11:08 PM on January 24, 2010

It's pretty hard to tell what's in that box. I'm guessing the stuff towards the right is terminals of some kind? Are there any screws or lugs visible over there? The solar panels I've worked with of that size are all screw/lug/crimp connections.

The wiring should presumably be done so that one of the solar panels' wires goes straight through to a battery terminal, and the other one goes through the reverse-protection diodes you have there and to the other battery terminal. (And through a fuse, since you mention it.)
posted by hattifattener at 11:15 PM on January 24, 2010

Response by poster: Here is the Auction. Unfortunately there isn't much to go on.

My panel has the same chords coming out as the link you posted, but not a built in box.

hattifattener: Yes towards the right are what I think are terminals, but there are no screws or anything. There is an thin seperation between metal in the terminal that a small flat screwdriver can fit into.

Thanks for the help so far.
posted by meta87 at 11:38 PM on January 24, 2010

One possibility is.. Stick a screwdriver in the smaller slot and that should retract the metal clip in the corresponding large slot. Then insert wire into the larger slot and remove the screwdriver, locking the wire in place.

However, sounds like you don't really need this device on your panel... Are you using it because you want the diode?
posted by Chuckles at 12:34 AM on January 25, 2010

Best answer: OK, so I did some searching on the internet and found this page. That's just a random page on the internet, and if it's wrong then so am I, so you should confirm all this stuff to your own satisfaction before doing anything that might be dangerous!

Anyway, assuming that page is correct, here's how I'd expect you to connect that junction box. The part of the circuit diagram looped by a thin blue line is what I think you have in that box. On the photograph on the right I've marked the connections you'd want to make to connect solar cells to match that diagram.
posted by Mike1024 at 12:42 AM on January 25, 2010

Best answer: Yeah, I've been puzzling over this for a couple of hours, and Mike1024's diagram is the only one that makes sense to me. What threw me is the MC connectors (not visible in the OP's pics, but visible in the eBay pics) - they're common on sealed PV panels, so it really does look like the panel is supposed to connect to the cable, not the terminals.

meta87: Can you tell on your box which of the MC connectors is connected to the lead marked as +ve near the box? How about on your panel; which one is marked as +ve there? IIRC, the female (recessed) connector should be the positive from the source. If on the box the +ve lead goes to the female connector, then that would suggest that Mike1024's diagram is right.

If he is, then you'll still need a blocking diode - Schotty, for preference, and a reasonably high-current one - to connect it to the battery, as per the uncircled diode in his neat piccy.

Other than that: yeah, those are push connectors in the box - they take a fairly heavy duty spade terminal or, at a pinch, multi-stranded wire. Not recommended for solid-core wires, as that combination will have bugger-all contact area. You insert/release the spade or wire by sticking a screwdriver into the hole to the left and levering to take the tension off.
posted by Pinback at 1:27 AM on January 25, 2010

I'm amazed the junction box came separate from the panel. This is a step I would assume the manufacturer would do - at least I've seen it done on similar panels. I echo what Pinback says though. Also pretty sure there's a sealant/adhesive that should attach the junction box to the back of the panel but not absolutely certain/can't remember exactly what it was, sorry.
posted by peppito at 1:55 AM on January 25, 2010

Eh, sorry, you're attaching a junction box to a battery, NOT the solar panel, just ignore what i said.
posted by peppito at 1:58 AM on January 25, 2010

Response by poster: Wow thanks for the help so far, especially for the diagram Mike1024.

On the junction box, the positive cord leads to the male mc connector. I can't check the solar panel till later today, but I will let you know.

The only reason I bought this junction box was because I thought it was what I needed to connect to the MC connector cords coming of of the solar panel. I purchased the solar panel off of ebay, so it might not be the most standard panel.

I totally forgot to mention that I also bought a solar charge controller. So this junction box will actually be connected to the solar charge controller, then that will connect to the battery. At least that's how I think it is supposed to be setup. Thanks again!
posted by meta87 at 6:45 AM on January 25, 2010

Given your last comment you purchased the wrong item. What you have a standard junction box that is mounted on the back of a 72-cell solar panel. It ties 3 sets of 24 cells each into a 72-cell chain with a bypass diode across each set of 24-cells. Bypass diodes protect the panel if its partially shaded. I don't believe its of any use to connect a panel (which already has a junction box) to a battery & battery controller. Typically only a manufacturer of solar panels would use this item.

Solar panels are really not yet at the point where they're plug & play with standard connectors. You need to break out the electricians tool box to hook them up. The MC connectors on the panel are designed to connect to other solar panels in a series string (typically 10~11 panels for a grid connected home system). The MC connectors at the end of a string are then connected to standard electrical wire within an electric junction box and that cable run goes back to the inverter (or charge controller in your case).
posted by Long Way To Go at 8:37 AM on January 25, 2010

Response by poster: Long Way To Go: Thanks for the reply. Looking at the ebay description it looks like you may be correct. That sucks. I'm not setting up a complex system. This is just one 80 watt panel I want to connect to one 12v deep cycle battery with a solar charge controller in between. I'm going to use it for camping.

The solar panel has no junction box, just 2 wires with MC connectors on the end. How would you recommend I connect the mc connectors to the charge controller, which just has 14g multi-stranded wire coming out? I guess I could snip the MC connectors off, but I'm not sure I might want them in the future.

Thanks again.
posted by meta87 at 10:08 AM on January 25, 2010

Best answer: Well you've got a matching set of MC connectors on your defunct junction box. You could cut them off and connect them to the wires on your charge controller. That way you can connect/disconnect the solar panel from the charge controller, you don't need to 'damage' the solar panel by cutting off its connectors and you get some use out of the junction box you bought on ebay so it doesn't feel like a waste.
posted by Long Way To Go at 5:58 PM on January 25, 2010

If you send some links to the actual models of charge controller, solar panel & battery I might be able to make some sense of it. But fair warning, I'm an electrical engineer but I haven't ever built a solar battery charging system.
posted by Long Way To Go at 6:02 PM on January 25, 2010

Response by poster: Thanks I ended up cutting the wires from the junction box and the panel seems to be charging! Much appreciated everyone.
posted by meta87 at 7:47 PM on January 25, 2010

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