question

sams-vans avatar image
sams-vans asked

What causes a scorched/burned terminal on an MPPT?

I added a 170w solar panel to my existing 100w panel, for a total of 270w running into a 75/15 MPPT.

This worked well for over a year; upon prepping the vehicle for storage I noticed that the charge controller was no longer working, and investigation revealed that the PV+ input terminal had burnt up into the plastic around the terminal connection.

My dealer informed me that the connection at the terminal had come loose and created the issue.

My question is: did the excess wattage from the solar array generate heat to the terminal and cause it to loosen?

Would going to a larger 100/20 MPPT resolve the problem?


Moderator's note: Condensed for clarity - jfc200603

MPPT Controllers
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

8 Answers
Justin Cook avatar image
Justin Cook answered ·

@SAMS VANS, an important note based on something you said ("clipped 5 strands of wire") that I had missed earlier: it sounds like the wrong type of wire was used, and this will cause the overheating issue. There is only one type of wire that is acceptable to use, and your note that only 5 strands were clipped from an 8AWG cable to allow it to fit into an 10AWG terminal indicates that the wrong wire was used. Screenshot from the MPPT manual:


image.png (185.3 KiB)
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Justin Cook avatar image
Justin Cook answered ·

@SAMS VANS, if your terminal is scorched or burned then you had a loose connection; your PV will not cause this, only failure to fully tighten the terminal to begin with or the terminal may have loosened over time if the installation is in a van or other installation subject to a high degree of vibration.

One thing I have seen in some installations is that the wire insulation is not fully stripped back and so the terminal is tightened onto the insulation rather than the wire; this faulty connection will cause arcing and heat at the terminal and, eventually, device failure and possible significant system damage.

As a side note, it is inadvisable -and in fact specifically advised against- to connect mismatched panels to a single controller. If you have a 100w panel and a 170w panel, each panel should be connected to its own controller.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

sams-vans avatar image
sams-vans answered ·

THANKS JUSTIN. YES I DO BELIEVE IT WAS CAUSED BY LOOSE CONNECTION. I NEED TO KNOW IF EXTRA WATTS FROM SOLAR COULD BE CAUSING CONNECTION TO LOOSEN AS IT IS RATED BY SPECS AT 220W AND I HAVE 270W. I KNOW CONTROLLER WILL NOT ALLOW OVER CHARGING EITHER WAY , BUT MAYBE IT CAN NOT HANDLE ETRA HEAT CAUSIN TERMINAL TO LOOSEN. HATE TO REPLACE AND NOT ADDRESS UNDERLYING ISSUE. ALL TERMINALS WERE INSTALLED WITH GREAT CARE IN AND TIGHTENED AND CHECKED 3X OVER.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Justin Cook avatar image
Justin Cook answered ·

@SAMS VANS, no, the addition of the mismatched panel would not cause the PV input terminal to overheat unless the wire itself was overheating, so if you're certain that your connection at the controller is good, you should check the system wiring on the PV side to ensure that you don't have a loose connection elsewhere. The 75/15 will not accept 8AWG at its terminals (maximum 10AWG) so either your wiring is different than you think it is, or you've trimmed strands from an 8AWG cable to get it to fit into a 10AWG terminal, in which case you could easily have a runaway strand that is arcing or some other very dangerous condition.

You should not run those mismatched panels into a single 100/20; as noted in my original reply, mismatched panels should not be connected to a single controller. Rather, you should put each panel on its own 75/15.

Also, as a moderator here and in the interest of furthering the knowledge base for others who might have this issue, I have edited your original post to make your questions clear and to remove the ALL CAPS. Please refrain from using all caps in the Community, as this makes the information and questions incredibly difficult to read, which makes it difficult for myself and other users to assist you or to find pertinent information in the future.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

sams-vans avatar image
sams-vans answered ·

Panels are wired parallel?

1 comment
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Justin Cook avatar image Justin Cook ♦♦ commented ·

@SAMS VANS Is that a question? I don't know how you have them wired.

If you have them wired in parallel, then yes, check all of their connections including especially the "y" connector or however you have them paralleled together.

If they are wired in series, then check their connections where they are connected in series.

0 Likes 0 ·
sams-vans avatar image
sams-vans answered ·

Sorry I am new to this. The wire is 8AWG five strands of wire were clipped at termial connection as directed by the dealer/designer (AM SOLAR). Heat shrink was then placed over the wire, terminal depth was measured and wires were stripped accordingly. The connections are all good. Still wonder if PV+ is getting hot and causing expansion / loosening of wire at terminal over time. And if going to larger mppt would fix problem. I was told mppt 100/20 can be used with 290W solar array and tech manuals confirm this. Solar array is wired in parallel as directed by dealer.


2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

sams-vans avatar image
sams-vans answered ·

Yes all connections are good. Contacted dealer and they assured me that although it may not be advisable to mismatch panels all the math has been done and panels are safely / correctely wired to the MPPT. My original problem is that yes PV+ became loose at mppt. Would the excess watts of solar array cause this to heat at terminal and loosen over time? And if so would going to larger mppt 100/20 which is rated up to 290w solve problem? Original

mppt was the 75/15 which is rated up to 220W.

2 comments
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Justin Cook avatar image Justin Cook ♦♦ commented ·

@SAMS VANS, as answered earlier, no, the loosening at the input has nothing to do with the panel wattage, so will not be solved by installing a larger controller.

0 Likes 0 ·
sams-vans avatar image sams-vans Justin Cook ♦♦ commented ·

Ok thanks ,I am going to replace charge controller with another MPPT 75/15 and going to take the position that the wire must have just come loose at the terminal on its own.I will double check all connections and check them all on a regular schedule as part of my maintenance routine in the future. Thanks for the help!

0 Likes 0 ·
sams-vans avatar image
sams-vans answered ·

AM SOLAR still takes the position that they stand behind their electrical sytem design/wiring. I have ordered a new charge controller and will be reinstalling with extreme attention to detail and monitoring the connections on a regular basis. If this problem should arise again the future I think I will be replacing the wiring between solar roof penetration box and charge controller. Thanks for all your help and knowledge in addressing this problem.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.