Grounding MPPT 100/50

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Matt Knight asked Jan 30, '19

Grounding MPPT 100/50

We are soon to be installing a Victron SmartSolar 100/50 in our RV. It will be connected to 4x 100W solar panels in a 2s2p configuration. Our travel trailer’s 12V ground is connected to the trailer chassis.

Do I need to connect the solar panel negative to the PV- on the Victron solar charger or can I instead connect PV- to the existing common ground (ie the chassis) and connect the solar panel negative to the common ground too?

This is how another MPPT Charger we have installed is wired but I see no mention of it in the Victron documentation. Doing this would simplify our cable runs.

solar wiring Grounding

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Guy Stewart (Victron Community Manager) answered · Jan 30, 2019 at 12:44 PM

You should connect the solar panel negative to the solar panel negative terminal on the MPPT. Do not use your grounded vehicle chassis to connect the negative of the PV string.

I understand this will mean an additional cable run.

From the Wiring Unlimited Draft :

Do not ground the positive or negative of the PV array: the PV negative input of the MPPT is not isolated from the negative output. Grounding the PV will therefore result in ground currents

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Matt Knight commented · Jan 30, 2019 at 12:50 PM

Understood - thank you! This is the information I was looking for.

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vivuscraig commented · Feb 01, 2019 at 08:11 PM

@Guy Stewart (Victron Energy Staff) Guy, can I ground from the controller directly to the chassis? From what I understand, the negative of the PV string should go directly to the controller. Also, the negative of the battery should go directly to the controller. So can I run the ground from the ground screw on the side of the controller to the chassis.

I think that is what you are saying.

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Guy Stewart (Victron Community Manager) ♦♦ vivuscraig commented · Feb 01, 2019 at 10:54 PM

Yes, you can connect the ground screw on the external case of the controller to the vehicle chassis.

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Answer 1 · 2019-01-30T13:16:27Z

Matt Knight answered · Jan 30, 2019 at 01:16 PM

@Guy Stewart (Victron Energy Staff) just following up, is a circuit breaker required on the positive output (battery) side of the charge controller? I assumed one was but I just noticed the specs show it contains “Output short circuit” protection. I will be including a breaker on the positive input (PV) side.

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Guy Stewart (Victron Community Manager) ♦♦ commented · Jan 30, 2019 at 01:18 PM

Best practice is to have a circuit breaker or fuse sized 75% below the current rating for every piece of wire.

In the case of the positive output on the battery side, a slow blow High Rupture Current fuse is appropriate, and should last the life of the installation.

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Matt Knight Guy Stewart (Victron Community Manager) ♦♦ commented · Jan 30, 2019 at 01:24 PM

That was my design but then I read that the charger has built in protection. I wondered if that were sufficient but it sounds like not.

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Guy Stewart (Victron Community Manager) ♦♦ Matt Knight commented · Jan 30, 2019 at 01:35 PM

There is some protection inside the units, but it isn't rated to the wire you connect. It is also not user replaceable, so you are FAR better off with a serviceable fuse.

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