Has anyone ever seen this before? I was asked to inspect a local farmer’s solar array which seemed to him to be underperforming. It was 8 x 150w panels that were only putting out about 550w on a good day. Everything looked fine from the outside until I checked the connector underneath the panels. The two-into-one MC4 adapter was melted. I replaced the adapter and found the panels to be putting out an acceptable 980w.

I’m trying to figure out why this would happen.... 

This happened to me about 2 years ago. One MC4 also melted like that. Turns out the cable was not crimped on properly.

8 hours ago, Solaris said:

I’m trying to figure out why this would happen.... 

It could also be mismatched MC-4 connectors. In Australia, they have to be the same brand; it's not allowed to mix different brands of connector. The theory seems to be that while cheaper (non-genuine MC-4) connectors would generally connect OK to each other, connecting to genuine MC connectors (MC is actually a trade name), or especially non-genuine brand A to non-genuine brand B, is much more likely to cause problems.

When you have Y connectors, you have three sets to match up: the panels, the Y-connectors, and whatever you use to connect the Y connectors to your cables. Sometimes there can be four, if the inverter has MC-4 connectors built-in.

I have every crimper for all possible applications but I don't know which one to use for these connectors.

My suggestion is to crimp the cable as best you can and then solder the wire to the connector as well. Soldering makes an excellent connection.. 

10 hours ago, Coulomb said:

whatever you use to connect the Y connectors to your cables.

This is where the problem appears to originate. I pulled the connector apart and it appears there was no solder and also I see rust inside.

GVC was right too in that there was no crimping

The Y-connector itself didn’t have an issue. The connection from the Y- connector to the cables going to the controller was the weak point. 

Thank you guys, this appears to be solved. 😁
 

On 2021/01/10 at 7:29 AM, Richard Mackay said:

My suggestion is to crimp the cable as best you can and then solder the wire to the connector as well. Soldering makes an excellent connection.. 

This is exactly what I have done. Crimp and solder together. I feel confident that it is now right. 👍

11 minutes ago, Vassen said:

Then I decided to buy a proper mc4 crimper. It actually is a lot easier and quicker with the crimper. 

Please post a pic of this crimper..

Thanks! I had a closer look at the MC4 connector. The actual socket (that you crimp) doesn't have a strain relief portion for the insulation of the cable (like the automotive connectors do). The strain relief mechanism is built into the plastic housing. So to complete the installation properly you need to screw the strain relief collar at the end of the connector to secure the cable.

The strain relief connectors that I have have a large diameter so I doubt if it will clamp cables with smaller diameters.

If the strain relief isn't tightened then all strain on the cable is borne by the crimped socket so this doesn't bode well for maintaining a good connection. 

On 2021/01/11 at 7:53 PM, Vassen said:

I’ve read somewhere that soldered joins are not recommended. Although they do make a good contact, they also tend to breakdown / “rust” ( can’t remember the correct term) over time.

I tend to agree with this. I have noticed that after a few years, certain things I have soldered tend to start rusting. My theory is that the heat of soldering compromises the tin plating of the metal.