copper wire corrosion

[894tom]

I have installed a solar power system for an off grid system. I completed this project around a year ago. I check the batteries every month or so for maintance purposes. I noticed that under the bright sun my charge controller was sleeping. I found the problem was one of the cables had corroded/disconnected to the point where it disconnected all incoming power to the charge controller. It had a black residue on it that I could wipe off with my fingers....Mold? Ash? I attached two photos of the pin that was removed from the Anderson connector.

How did this happen?

Couple points to consider:
The system is a portable system that is based on a trailer.
The trailer has just under 1200watts of solar panels.
The panels are run in series at about 120vdc.
Due to its mobile purpose I use Andersen plugs as quick disconnects that are exposed to the elements.
The circuit breaker did not trip.
The lead that was corroded was the positive lead.

[inetdog]

I have installed a solar power system for an off grid system. I completed this project around a year ago. I check the batteries every month or so for maintance purposes. I noticed that under the bright sun my charge controller was sleeping. I found the problem was one of the cables had corroded/disconnected to the point where it disconnected all incoming power to the charge controller. It had a black residue on it that I could wipe off with my fingers....Mold? Ash? I attached two photos of the pin that was removed from the Anderson connector.

How did this happen?

Couple points to consider:
The system is a portable system that is based on a trailer.
The trailer has just under 1200watts of solar panels.
The panels are run in series at about 120vdc.
Due to its mobile purpose I use Andersen plugs as quick disconnects that are exposed to the elements.
The circuit breaker did not trip.
The lead that was corroded was the positive lead.

Points to consider in looking for the solution:

1. The PowerPole connectors are not sealed in any way, so they are not ideal for use exposed to the elements. Especially if water can puddle around them or if the + and - connectors are stacked together.
2. Did you crimp or solder the wires? If you soldered them, did you use acid-core solder or acid type flux? This will leave a residue which can eventually corrode the wires.
3. Any DC wiring which is exposed to the weather is subject to leakage currents, especially if the water surrounding them is not clean, but possible even with just rainwater. At 120 volts, the leakage current can be quite high. Especially if the + and - connectors are mounted side by side, as is commonly done with Anderson PP connectors.
4. DC leakage currents can cause copper to dissolve at the + side and plate onto the - side. The plated side is not harmed (much) while the + side corrodes away. This is the reason that Telcos have used positive-ground for their DC power.

Some suggestions:
1. Use a different connector type which is specifically weather tight. Or
2. Put a weather tight covering around the connectors, and keep them clean at all times, and/or
3. Keep the + and - connectors separate from each other and any conductive surfaces. The insulation will prevent short circuits but not leakage.

[Sunking]

Pretty typical of DIY jobs you used the improper terminals, tools, and installation technique. You are lucky you did not have a fire.

[894tom]

Pretty typical of DIY jobs you used the improper terminals, tools, and installation technique. You are lucky you did not have a fire.

I dont know what could have caught fire. The Anderson connectors are at the end of a 12ft. wire run with nothing flamable nearby. I have asked around but have not heard any suggestions for the proper watertight terminal(s). I had the Anderson plugs put on the wires professionally. They were crimped and soldered out of my view and have no idea how they did it or what type of solder they used about nine months ago. What I can say is that I stripped off the cable and found a brown powdery substance where the wire once was.

I would love to hear suggestions on the proper type of plug/terminal.

[inetdog]

I dont know what could have caught fire. The Anderson connectors are at the end of a 12ft. wire run with nothing flamable nearby. I have asked around but have not heard any suggestions for the proper watertight terminal(s). I had the Anderson plugs put on the wires professionally. They were crimped and soldered out of my view and have no idea how they did it or what type of solder they used about nine months ago. What I can say is that I stripped off the cable and found a brown powdery substance where the wire once was.

I would love to hear suggestions on the proper type of plug/terminal.

Well, the industry standard for PV these days is the MC4 connector. And it has been around a lot longer than 9 months. It incorporates a watertight seal, is designed for outdoor exposure in terms of UV resistance, etc. It provides a safe insulation for handling the high voltage DC around both male and female connectors when they are unplugged. The asymmetric design makes it harder to accidentally reverse polarity when connecting. It is UL tested for this specific use, although it should not be used to disconnect under load, if that is what you intend to do. A switch or CB is much better for that purpose!

I suspect that the professional was more familiar with RV use (12 volt) than with PV and high DC voltages. Otherwise he would have talked you out of using them in the first place.

The brown powdery substance is probably copper oxide and is what is left after the metallic copper has left the building (moving as copper ions under the influence of the electric field.)

[RussN9ZP]

I dont know what could have caught fire. The Anderson connectors are at the end of a 12ft. wire run with nothing flamable nearby. I have asked around but have not heard any suggestions for the proper watertight terminal(s). I had the Anderson plugs put on the wires professionally. They were crimped and soldered out of my view and have no idea how they did it or what type of solder they used about nine months ago. What I can say is that I stripped off the cable and found a brown powdery substance where the wire once was.

I would love to hear suggestions on the proper type of plug/terminal.

High resistance connections like the ones you have there can cause a fire. Andersons are good for indoor but not outside.

[megabyting]

The corrosion is due to the unsimilar (incompatible) metal contact. The copper in this case became sacrificial metal at the anode terminal. Using bi-metal wire and aluminium lugs may stop this kind of corrosion in a DC system. The anode is where the chemical oxidation takes place, and vice verses for the cathode. Copper wire is OK for AC system without DC bias because there is no permanent anode in the system.

[Sunking]

Why are you digging up a 5 year old thread? Highly suspicious for a 1st time poster.

[sdold]

I do the same thing sometimes, search for interesting topics or keywords, find something I might know something about, add a post, and then figure out that I've resurrected an old thread. It's embareassing.

[SunEagle]

Why are you digging up a 5 year old thread? Highly suspicious for a 1st time poster.

I checked to see where that poster was from and they are on my watch list for future spam posts.

[Sunking]

I checked to see where that poster was from and they are on my watch list for future spam posts.

Smart move.

[megabyting]

I was investigating the outdoor copper - aluminium corrosion problem. Bi-metal lugs were used to join the copper and aluminium conductors but the aluminium cable was eaten away in just 2 years of service. The solution is to add a moisture barrier to the joint to prevent the dissolve copper oxide flows on to the aluminum conductors. I don't know it is an offence to dig up an old post. Sorry for the inconvenience.

[SunEagle]

I was investigating the outdoor copper - aluminium corrosion problem. Bi-metal lugs were used to join the copper and aluminium conductors but the aluminium cable was eaten away in just 2 years of service. The solution is to add a moisture barrier to the joint to prevent the dissolve copper oxide flows on to the aluminum conductors. I don't know it is an offence to dig up an old post. Sorry for the inconvenience.

It is not against the rules to resurrect an old post. The problem is that most "spammers" like to add their "new" post to an old thread which is the start of them doing things we don't like.

Thanks for your input and welcome to Solar Panel Talk.

[sdold]

I don't know it is an offence to dig up an old post. Sorry for the inconvenience.

Thanks for joining and for your contributions. Even if the original poster is long gone, adding to the information repository is useful for future readers, which is why we don't delete all of the old threads as soon as all of the questions were answered. Welcome to the forum. If you stick around long enough you'll see examples of what Sunking and SunEagle are talking about.

[Sunking]

OK use No-Ox-Id Special A grease. Absolutely no better product money can buy and it is cheap. A small tube will last a lifetime unless you are a pro using it every day. If used correctly will last longer than your kids will live.

Additionally if you are going to use aluminum wire all terminal equipment must be rated AL/COR. Do not use anything rated AL/CU.