Grounding Mobile Solar

[WilliamH]

Question 1: I am building a solar light trailer. I have two 250W 60 cell modules with Vmp of 30.1V. (I would have bought 72 cell modules, but these were donated) Is it all right to put them in series which could exceed 80Voc in cold temperatures. I don't know why, but I was under the impression that mobile solar was not to exceed 50V DC.

Question 2: The charge controller is a Morningstar PS40 MPPT. It has a system ground terminal that the manual says must be bonded to a permanent earth ground. Can the trailer frame safely take the place of the earth ground?

Question 3: Do the module frames and other metal components have to be bonded to the trailer frame?

Question 4: Why is there no mention of grounding in the mobile systems displayed on the this website? Am I missing something?

Again...I'm new to mobile solar.

Thanks

 

[KBWaldron]

Search for grounding. There are a number of threads on this topic with good information.

 

[WilliamH]

Search for grounding. There are a number of threads on this topic with good information.

Thank you KB. I'll give it a go.

 

[erik.calco]

Search for grounding. There are a number of threads on this topic with good information.

I searched for grounding and found your post. ?

 

[WilliamH]

I think that is called irony.

 

[KBWaldron]

I searched for grounding and found your post. ?

I assume you found the other posts as well. ?

 

[erik.calco]

I assume you found the other posts as well. ?

No. I got exhausted lol ?

 

[KBWaldron]

I’m concerned that you may not know of the search function. Upper right of screen is a search button. Search all forums for grounding. My apologies.

 

[WilliamH]

I found a video of William Prowse explaining grounding on one of his You-tube videos. I'll share it with you all this weekend. I'm not at home right now.

 

[WilliamH]

Here it is. It answered some of my questions.

I did continue my search and learned some more from other sources. I was able to find the answers to most of my questions. I'll give it a go:

(Disclaimer: Please remember that I am a beginner with mobile solar and I am conveying what I have learned from sources that I believe to be legitimate. If any of you out there with more experience see errors here, please let me know. I hope to get this right for my project and to share with others what I learn. I am not disclosing my other sources in case my understanding does not accurately represent their explanations)

1. Non-current carrying metal: Each component in your system that has metal parts that are not part of the electrical circuit (and should not be energized), must have a grounding terminal or lug that gets bonded to the chassis of your vehicle. This would include, but is not limited to, the frame of your modules, the chassis of your charge controller, the chassis of your inverter, the chassis of metal light fixtures etc. This is very much like the equipment ground of a residential system but is done to keep them all at the same electric potential.
2. Current carrying conductors: The negative current carrying conductor must get bonded to your vehicle chassis at only one location. It can happen on the solar side or on the battery side, but not both. This is called the system ground. The manual for my MPPT controller clearly states that you cannot connect the negative terminal of the controller directly to Earth Ground (which in this case is the vehicle chassis). Usually the negative terminal of the battery is where the system grounding to the vehicle chassis occurs.
3. Maximum Voltage: Your charge controller will have a voltage window. It will not turn on if the voltage from the array is too low. It will damage the controller if it is too high. My MPPT controller has a max voltage of 120v. My two modules have a Voc of 36v (at standard test conditions) but a Vmp of only 30.1v. You need about 34v to charge a 24v battery bank, I cannot wire my two modules in parallel, because they will not produce enough voltage (especially on a hot day) to charge my 24v battery bank. I was worried about wiring them in series because the array would exceed 50V. According to my most reliable source, this is not an issue if you have a MPPT controller. That is because the controller will drive the array voltage down to just above the voltage needed to charge the battery bank. Also, When the batteries are not charging, the MPPT controller will open the array circuit. Furthermore, the 50v limit only applies to systems that are not grounded, So, as usually, I was likely worrying for no reason.
4. If you don't ever hear from me again, well... you might want to find your own sources for understanding mobile grounding.