Hey everyone, looking to see if any other Axpert users are experiencing this.

Hardware:

Conversol 11kW Max

Array of 6x 400W panel, array of 5 + 5 400W parallel panels with anti-reverse diodes

5 x 5kW LiFePo 51.2V batteries

Unit operating on battery only, internal inverter mains contactor open.

Recently I went to install some extra end mounts to my aluminium solar roof bars that the panels are connected to. When I touched the bars I got a continuous very uncomfortable buzzing feeling (I did it at night as I knew there could be capacitance when the panels were producing). Grabbed a fluke and checked and there appears to be 70V AC on the roof bars. Anyone have any theories why this would happen? I didn't ground the bars when I was installing as I knew the system was transformerless, but I'm questioning whether this was the correct move now. Any advice appreciated.

 

PS I also seen another post elsewhere where someone got a jag from their metal roof, they were also using a 5kW axpert inverter:

Link to post

What roof type tiled or corrugated? Are the solar roof mounts grounded with at least 6mm² wire to a earth spike? If it persist you need to use more than one earth rod. Is both strings earth's tied together. Is your inverter input and output terminals earthed?

Roof type is slate tiles, supports are bolted into wooden rafters (So relatively well insulated). Inverter input and output terminals are earthed. The panel frames and the associated bars are floating, not earthed. From memory (I installed a couple of years ago now), what I inferred from the Axpert manual was that the panels should not be tied to earth because it's not a galvanically isolated inverter. Willing to be corrected if that's been misinterpreted though!

Edit, found the manual text:

Edited August 22, 20241 yr by Phalanxer
Minor text correction

10 hours ago, Phalanxer said:

Roof type is slate tiles, supports are bolted into wooden rafters (So relatively well insulated). Inverter input and output terminals are earthed. The panel frames and the associated bars are floating, not earthed. From memory (I installed a couple of years ago now), what I inferred from the Axpert manual was that the panels should not be tied to earth because it's not a galvanically isolated inverter. Willing to be corrected if that's been misinterpreted though!

Edit, found the manual text:

The above refers to PV source not to be grounded( neg of modules) array equipment must still be grounded, but not the PV source. So the negative from the pv array must not be grounded. The actual mounting rails that holds the pv modules in place must be grounded otherwise no COC.

You need to always ensure that there is no dc leakage between modules( micro cracks or faulty panels) leaking dc to the mounting rails. This normally occurs during wet weather hence the reason i do IR test on each panel before installation.

Thanks for the clarification, I'll look at installing an earth to the equipment. I also can borrow an IR tester from work, I'll test the panels to make sure no leakage. Is it possible to bond the panels to the DNO earth or is it advisable to drive a spike for a local earth?

Yes, those high PV voltage models are nearly always non-isolated (certainly for all Axperts). So there is a large 50 Hz potential between PV- and earth. PV+ would also be lethal even at night, I would think.

Presumably, non-earthed rails would get some fraction of that from capacitive coupling.

Always disconnect PV panels from a running inverter, even at night, to work on them. The PV inputs are not passive!

Thanks Coulomb, that's good advice.

I checked the local regulations and it's OK to continue to use the DNO (Distribution Network Operator) earth even when in island mode. However it did unveil a topic I hadn't considered before. When disconnecting from the DNO supply, it will mean the earth and neutral are no longer bonded at source, leaving a floating neutral. Do the internal mechanisms of the Axpert inverters bond the earth and neutral automatically when the DNO is disconnected?

Edited August 23, 20241 yr by Phalanxer

8 hours ago, Phalanxer said:

When disconnecting from the DNO supply, it will mean the earth and neutral are no longer bonded at source, leaving a floating neutral. Do the internal mechanisms of the Axpert inverters bond the earth and neutral automatically when the DNO is disconnected?

If you mean when the AC-in and AC-out ports are no longer connected, do the Axperts bond AC-out neutral to earth, the answer is yes. Though there is a screw inside that apparently can be removed to thwart this, so check with a multimeter that AC-out neutral connects to earth when the inverter is totally unpowered.