question

mbonnar avatar image
mbonnar asked

chassis grounding clarification

Hola,

Yesterday, I received a SmartSolar 100/50 charge controller ordered thru Amazon. It's to be installed in my RV. Going over the manual (version 02, Sept. 21st 2017), section 3.2 states 'The charger must not be connected with grounded PV arrays (one ground connection only)'. Does this mean I should not be grounding my solar panel frames to the RV chassis? My plan was to ground the solar panel frames to the RV frame in one location and ground the charge controller housing to the RV frame at another location. According to the statement in the manual, this should not be done. Please clarify the statement for me so I have a better understanding. Thank you for your time.

Kind regards,

Michael Bonnar

chargerGrounding
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gazza avatar image gazza commented ·

What I think they are getting at by the phrase.. 'The charger must not be connected with grounded PV arrays' is that you DON'T ground the -ve side of the PV, it is ok to ground the metal frame of the panels (which is isolated from the whole power generation -ve and +ve)

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ripper avatar image
ripper answered ·

They want two wires running from the solar panel to the mppt. As the frame of the panel is isolated from the wafers that are making the electricity you can ground the frames to the chassis as much as you want and bolt the mppt anywhere you want too. You also need two wires running to the battery as the unit is also isolated against the mounting holes.

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mbonnar avatar image mbonnar commented ·

That is my understanding, the manual is not specific.

Thanks for your input. Have a wonderful day.

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rjoustra avatar image rjoustra commented ·

Okay on this note I have an additional question. My four charge controllers chassis are bonded with my inverter chassis and will be bonded to my solar panel frames and then to the chassis of the coach, but my question is this is installed in a motorhome and my battery negative buss bar is also grounded to the chassis. Both positive and negative wires for each array go through DC breakers. Am I missing anything?


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Kevin Windrem avatar image Kevin Windrem rjoustra commented ·

You are good as long as neither the positive or negative leads to the INPUT of the MPPTs are not grounded

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rjoustra avatar image rjoustra Kevin Windrem commented ·

The mppts are landed on the buss bars which ultimately go to a chassis ground vis the buss bars. Is this right?

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Kevin Windrem avatar image Kevin Windrem rjoustra commented ·

Yes you should be connecting the system DC negative bus to chassis ground somewhere (just one place).

The Victron manual states that the MPPT chassis is NOT connected to battery negative, so if you want the chassis grounded, you'll need to do it yourself. But from the wording it sounds like it is not required.

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rjoustra avatar image rjoustra Kevin Windrem commented ·

Yes I daisy chained the MPPTS chassis’s’ together and plan on taking the to the same motorhome chassis ground point my inverter chassis are grounded to and ultimately the PV frames. Will this cause an issue with my mppts since the negative buss bar and frames and device chassis all land on the motorhome chassis. Or should I forgo any of the above being chassis grounded to the motorhome

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Kevin Windrem avatar image Kevin Windrem rjoustra commented ·

No, since the MPPT chassis are not connected to the battery negative.

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rjoustra avatar image rjoustra Kevin Windrem commented ·

They will be via the motorhome chassis connection since the buss bar I also ground to the motorhome chassis. I guess that’s why I’m confused.

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gazza avatar image gazza rjoustra commented ·

Check out the picture I posted below. What you have done is fine. The chassis of the MPPT is isolated from the PV inputs. What you DON'T do at any point is ground one side of the PV -ve and +ve , those terminals are also isolated from the panel frames so it is ok that the "frames" of the panels are bonded to ground. I hope that is clear?

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gazza avatar image
gazza answered ·

From Victron publication "Wiring Unlimited":-

Off-grid system grounding.

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. The PV frames however may be grounded, either close to the PV array or (preferably) to the central ground. This will provide some protection against lightning. Ground close to the battery. The battery poles are supposed to be safe to touch. The battery ground should therefore be the most reliable and visible ground connection. The DC ground cabling should have a sufficient thickness to be able to carry a fault current at least equal to the DC fuse rating. The chassis of the inverter or Multi/Quattro must be grounded. There is basic insulation between AC and chassis. The chassis of the MPPT solar charger must be grounded. There is basic insulation between AC and chassis.

Please note that the AC distribution with fuses or MCBs and PV array and PV frame grounding are not shown.


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Mark Anderson avatar image
Mark Anderson answered ·

what did you end up doing? I’m also confused by the fact that binding things to chassis and connecting battery negative to chassis is essentially binding to the battery negative (the chassis is a huge bus bar)

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Fideri avatar image Fideri commented ·
@Mark Anderson
Did you ever resolve this? I have exactly the same confusion. Ultimately, everything is interconnected via the central negative busbar.

Fideri

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Mark Anderson avatar image Mark Anderson Fideri commented ·

unfortunately not

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Fideri avatar image
Fideri answered ·

Thank you @Mark Anderson and @Gazza for your replies. All done following Wiring Unlimited and the specific manuals. I was confused by @Kevin Windrem comments, repeated twice, that the battery negative is not to be grounded. I read my MPPT manual again. It only mentions the solar panels in this context. I guess Kevin meant the panels.

Fideri

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Kevin Windrem avatar image Kevin Windrem commented ·
Sorry for the confusion. My comments were intended to mean that the battery negative is not INTERNALLY connected to the MPPT chassis.


Of course the battery negative SHOULD be connected to the system chassis and the MPPT chassis SHOULD be connected to the system chassis.

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Fideri avatar image Fideri Kevin Windrem commented ·
Thanks @Kevin Windrem. All clear and good now.
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Mark Anderson avatar image
Mark Anderson answered ·

@Fideri so you DID connect the battery ground to the chassis?

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Fideri avatar image Fideri commented ·
@Mark Anderson
Yes.
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