Battery Grounding?

[leaves]

Hi there

Is it important to ground a battery system?

On the negative pole.

Thank You

[Wetkit]

Hi Leaves,

I think according to wiring regulations it is required.

Perhaps somebody who have done commercial installations could give better advice.

I would think that it is extremely important to do it in area's where lightning can occur, or if you have high PV panel voltages present.

 

Here is a schamatic I found on-line.

 

[leaves]

Hello

Can you help me understand the difference between positive and negative grounded components?

How would this affected battery grounding with a component in the solar system that has positive grounding?

Thank you

[BenDL]

If you are talking about the DC side, then you would not ground either the positive or the negative.

(By Grounding do you mean connecting to the system earth? Alsorefrred to as earthing?)

 

The schematic provided by Wetkit also does not show any grounding of the DC side.

It clearly shows running two conductors from the solar panels to the batteries.

 

Motorcars use negative grounding just to save on the use of conductors - the body of the car is used as one conductor.

(Some olde cars used positive grounding, proabably just to be different & to confuse the lawyers...)

 

I hope I have inderstood your question correctly?

[Wetkit]

@ BenDL,

I think you need to re-look the shematic a bit better. There is two grounding points, one via a surge arrestor and another via a breaker, both of these going to the common DC negative bar.

 

@ leave, I have only seen Positive earths on very old 6V cars. It was believed to help stop the metal rusting.

The Yanks might do positive earthing, as you know they do everything in reverse.

If you do have a component in your system that have positive grounding, do not ground the negative then. Something will go BANG!

 

The only reason for grounding the DC side, positive or negative, is to allow a safe return path for high static discharges, like with a lightning strike.

Would you really like a lightning charge to run through your complete system? Might not look too good afterwards

 

Perhaps an installer could comment on Positive grounding?

[leaves]

Thank You

I have noticed with my radio equipmet that has negetive grounding.

When I hook the DC radios onto the positive side of the battery only the radios powers up.

I would love to understand the physics of this. I belive the equipment does not know the diffeence as it is getting charge from the battery?

But how does this lack of voltage not going into the negetive end of the battery affect it?

Thank you

[BenDL]

Hmmm, the diagram. Yes, if you have a surge arrestor that will have to be connected to the body of earth. (But the negative pole of the battery is not earthed)

 

What leaves asked:

"Should the negative terminal of the battery be earthed/grounded?"

 

I see no advantage to doing this.

 

Ben

[Wetkit]

Right, so I spent some time on Google and read up a bit on the subject, as it seems to be a bit of an issue.

Here is some links for your own benefit, granted they mostly from the US.

http://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-grounding-dc-systems

http://www.solarpowerworldonline.com/2012/04/installation-practices-keep-your-pv-system-well-grounded/

http://www.nmsu.edu/~tdi/pdf-resources/CC102.pdf

http://www.nmsu.edu/~tdi/pdf-resources/CC103.pdf

 

http://www.solarabcs.org/about/publications/reports/systemgrounding/pdfs/SystemGrounding_studyreport.pdf

 

What it really comes down to, is that ALL exposed metal parts of any electrical system, be it AC or DC, needs to be grounded. That is the law.

 

It is also stated, that if your PV voltage is higher than 50V, the positive, or negative, of the PV needs to be grounded. And this is where the probelms start.

Go and have a good look at your MPPT, and you will find the negative input and output is common. So when you grounding the negative of the PV side, you in effect grounding the battery negative as well, through the MPPT controller.

When we move over to the Invertor, you will find that the older type invertors that have an isolating output transformer, the DC negative is also grounded to the invertor chassis.

The newer type transformerless invertors seems not to do this.

 

So, at least ground all the metal parts. What is reccomended as well, is to have the PV ground wire seperate outside the building to an earth spike. Incase of a lightning strike, it will keep the flash outside your building while traveling down the earth wire, and not be a fire risk inside the building.

[leaves]

Wetkit , spoke to a few guys, i think you spot on.

System grounding is essentail for a safe system.

Thank you, nice to learn all these things.

I was reading that the best way to ground is with x shape water pipe in ground placed horizontally just under the surface.

This sound okay?

[Wetkit]

The law states that any grounding point should measure 1Ohm or less.

Probelm is that to measure this, you need specialised equipment.

 

Now, just sticking stuff in the ground might looks like a ground point, but does it measure correctly?

 

The way to do gounding correctly is to make sure you know the type of soil you working wiith.

Here where I live, we have just sand, which is a very poor conductor, so we have to put stakes in the ground, some up to 6m deep, to get the correct readings. Sometimes you have to combine multiple stakes to get the reading low enough.

 

Last year we did a project at Nigel where we had to install around 1000m of earth cable around the buildings foundation to get the correct ground resistance.

 

Best would be to talk to your local electrical contractors and find out what they do in your area.

[Wetkit]

Right, getting back to this topic

To date I have NOT got round to eathing my own system as yet.

Now over the week-end I installed an new 48V invertor and changed my battery configuration to 48V as well.

While going over the battery connections, I sunnely got a very nice wallop from the battery terminal. It did not veel like an DC hit, so what the hell?

Later I got another lekka wallop from the battries

 

Got my meter out and started measuring, getting 190V AC between my battery terminals and Ground!

My best guess is it is the invertor switching noise creating this AC voltage on the DC side.

I measure it all the way to the solar panles as well.

 

My concern right now is that if I do earth the negative, could the AC jump to 380V on the posative???

 

Anybody had a similar problem?

[leaves]

wow. Could it be a short circuit in your Inverter?

L

[___]

I've seen the same thing. On my Victron inverter, it has a relay that disconnects ground and instead grounds to the case of the inverter when the grid-power is out (this has to do with boats and all sorts of corrosion to the boat itself if you ground to shore power), there is quite a bit of potential difference between the inverter case and actual ground, that is unless you ground the case itself. The current isn't very high, but it is there nonetheless.

[Sammyigt]

Wekkit has hit the nail on the head here.

Grounding of any exposed metal part is not only a safety factory but it is also the law. 

PV panels do also need to be earthed individually using an earth cable of equal or greater diameter to that of your DC PV cable, from there a 16mm earth cable needs to run outside the building to an array of Earth spikes.

[RikH]

Not sure. Since @Wetkitassumes one should earth the negative side of the panels. I don't, never. But I do earth the panels framework and mounting rails etc. So if you don't earth the - PV the batteries are also not earthed via the mppt. Just my thoughts.

Nice topic, thanks for bringing it up @Sammyigt.

[Wetkit]

@RikH, at no point did I say you must ground the negative of your PV panels, or you battery for that matter!

If you do that, something will blow up or end up killing somebody!!!

As @Sammyigt mentioned, all your PV panels needs to be grounded.

[RikH]

3 hours ago, Wetkit said:

at no point did I say you must ground the negative of your PV panels, or you battery for that matter!

Ok, I misunderstood that because I read to quick often. Like this:

On 2013/08/08 at 7:35 AM, Wetkit said:

It is also stated, that if your PV voltage is higher than 50V, the positive, or negative, of the PV needs to be grounded.

But when you don't continue reading you miss the part:

On 2013/08/08 at 7:35 AM, Wetkit said:

And this is where the probelms start.

Anyway, did you ever found the cause of this:

On 2013/10/28 at 3:22 PM, Wetkit said:

Got my meter out and started measuring, getting 190V AC between my battery terminals and Ground!

My best guess is it is the invertor switching noise creating this AC voltage on the DC side.

I measure it all the way to the solar panles as well.