farmerbrown avatar image
farmerbrown asked

Grounding MPPT 100/20 on aluminium trailer boat

I am in the process of putting 2 x 100 W solar panels on my 7 metre aluminium trailer boat. I may add additional panels at a later date. I see that there is a screw for attaching an earth wire to the solar controller. I have a 12 volt DC system and all electronics are wired positive negative to the house battery. Do I earth the solar controller directly to the negative on the battery? or should I earth to the hull? If I earthed to the hull wouldn't this lead to electrolysis? What happens if I do not attach an earth wire to the solar controller? Looking forward to your feedback

MPPT Controllers
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2 Answers
tilo avatar image
tilo answered ·

If the battery negative or let´s say DC circuit negative is not connected to the hull (earth), there is no point in connecting an earth cable from the charge controller earth point to the negative battery pole, as you would still be without connection to earth (the hull). If you want to connect earth, you need a connection at some point to the hull, either directly from the charge controller to the hull, or via the battery pole and from there to the hull.

The solar controller will work with or without the earth cable.

In terms of electrical safety I don´t think there is a problem if you do not connect an earth wire to the solar controller, as there are only low voltages involved.

Regarding electrólysis of the aluminium hull, I think that is more of a problem if your hull is connected to an earth cable from the shore (with AC), or with another metal piece of more noble metal with water contact. I am not from the boating world, it is just a theoretical consideration, without practical experience behind. If you are not sure, I would not connect an earth cable, to avoid this electrolysis topic.

You might connect an earth cable to your solar panel frames (if the panels have aluminum frames) to help discharge a possible atmospheric lightning current to the hull and water.

You could have a look at this Victron document about cabling (which is still in preparation):

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tilo avatar image tilo commented ·

After reading the following article (mentioned by JohnC in another topic) I recommend connecting DC negative to the hull, to avoid a possible corrosion of the hull.

If the boat is not in the water most of the time, it is probably less important.

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kai avatar image
kai answered ·

The electrolysis issue is that the earth wire (bonded to your hull at one end and connected to the shore earth on the other) allows for a circuit to be formed between your aluminium hull and other hulls also electrically connected to the same shore earth.

Removing the earth wire has safety implications if you also have 120/240vac onboard as well (not clear from post).

i recall there was a section on electrolysis w.r.t. boats at the back end of the referenced victron doc - if you have 120 or 240VAC onboard then look at the section for the suitable mitigations against electrolysis but still retaining the earth protection.

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