What is 'Common Negative' Solar grounding?

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UKNZ

25 posts

Geek

#245395 1-Feb-2019 18:50

Hi all

I'm building a solar system for my van, and my new Solar controller says it requires 'Common Negative' grounding. Even Google cant seem to help me with what this is and how to do it. Does anyone know what this term means exactly? Dont want to fry my new MPPT unit.

Thanks

Simon

DarthKermit

5346 posts

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#2171392 1-Feb-2019 18:57

I think this means your vehicle needs to have a chassis that is negative.

UKNZ

25 posts

Geek

#2171437 1-Feb-2019 19:08

thanks.

So I ground the negative battery -> MPPT wire to the chassis?

Whats the 'common' bit?

UKNZ

25 posts

Geek

#2171439 1-Feb-2019 19:17

Just found this when googling, which comes close to explaining it, but now I'm more confused than ever ...

Many solar controllers have positive ground; meaning that the solar panel + and the battery + and the contollers's load terminal + are all connected in common. The term ground in this case is the zero reference voltage. These connections are isolated from the vehicle chassis. So, in this case, for example, you would not connect the solar panel Negative (-) to the chassis.

Confusingly, the same term "ground" applies to the vehicle return path. So, loads connected to the vehicle battery and the house/aux battery are wired normally - a 12v fridge, for example. The negative is "grounded" to the chassis because that is the return "wire" for the circuit.

When you wire your solar controller, follow the connection instructions and don't be tripped up by the confusing use of the word "ground."

Aredwood

3885 posts

Uber Geek

#2171773 2-Feb-2019 13:19

UKNZ:
Just found this when googling, which comes close to explaining it, but now I'm more confused than ever ...

Many solar controllers have positive ground; meaning that the solar panel + and the battery + and the contollers's load terminal + are all connected in common. The term ground in this case is the zero reference voltage. These connections are isolated from the vehicle chassis. So, in this case, for example, you would not connect the solar panel Negative (-) to the chassis.

Confusingly, the same term "ground" applies to the vehicle return path. So, loads connected to the vehicle battery and the house/aux battery are wired normally - a 12v fridge, for example. The negative is "grounded" to the chassis because that is the return "wire" for the circuit.

When you wire your solar controller, follow the connection instructions and don't be tripped up by the confusing use of the word "ground."

You have answered your own Question.

Common negative grounding is simply having all negatives linked to ground. And all switching / fusing / control done on the positive side.

Common positive systems can be a massive can of worms. As the negative terminals of different devices are all at different voltages in a common positive system. And you have to be extremely careful to avoid unintended current paths between different devices. Especially as vehicles are designed to be common negative from the factory.

MichaelNZ

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Integrity Tech Solutions

#2171862 2-Feb-2019 15:46

Common negative grounding is as others have said. But quite frankly, do not electrically ground it.

Connect your solar panel to the charger controller via 2 fuses - one in the +ve line and one in the -ve line and your are good.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

Aredwood

3885 posts

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#2171913 2-Feb-2019 16:28

MichaelNZ:
Common negative grounding is as others have said. But quite frankly, do not electrically ground it.

Connect your solar panel to the charger controller via 2 fuses - one in the +ve line and one in the -ve line and your are good.

What purpose would those fuses do? As most solar panels only have a very small difference between their output current at Max Power Point. And their short circuit current. For example, I have a 270W panel that is rated to 8.57A at MPP. And 9.3A Short circuit.

You only need fuses on solar panels where you have multiple panels in parallel. Then you need to install the fuses into each branch.

Of course you definitely need a fuse between the controller and the battery. Assuming you have the common negative system, only fuse the positive cable to the battery. And as close to the battery as practical.

UKNZ

25 posts

Geek

#2172032 2-Feb-2019 23:21

Thank you @Aredrood and Michael, my faith is restored that I can do this! The terminology is confusing, but the concepts make sense, and the extra info was useful, thank you.