So I recently got an RCT Axpert VMIII with a Pylontech UP5000 as a UPS for loadshedding.

 

When connected to the grid, the output of the inverter seems normal with 230V between live and neutral, 230V between live and earth and almost 0V between neutral and earth.

However, when Eskom cuts out and the inverter is running from the battery, the output changes: 230V between live and neutral (normal), BUT 115V between live and earth and 115V between neutral and earth. Because there is still 230V between live and neutral my appliances seem to be working fine, but I'm not comfortable with a neutral that is not close to earth all the time.

I have an earth wire connected from the main DB to my inverter and battery. The output of my inverter leads to a wall socket, which is also connected with the same earth wire.

 

Have I wired something wrong or is this normal?

Please help.

When mains disappears you should, on the output of the inverter, with a relay, take neutral to ground, but this should not be connected, when Eskom supplies power, as far as I know. But do a bit of research about this 1st, before following my suggestion here...

 

10 minutes ago, Kalahari Meerkat said:

When mains disappears you should, on the output of the inverter, with a relay, take neutral to ground, but this should not be connected, when Eskom supplies power, as far as I know. But do a bit of research about this 1st, before following my suggestion here...

 

You are spot ON

Thanks!

 

I'll try the above and give an update once I'm done.

 

Cheers for now.

18 hours ago, Wiggly Electron said:

Have I wired something wrong or is this normal?

It sounds like you have it wired correctly, but this is not normal or safe.

When everything is powered down and isolated, you should see zero ohms between the inverter neutral output and inverter earth. Unless the inverter is older than about 2017. But I don't think any VM IIIs are older than that.

I suppose it's possible that you have a faulty relay RY1, or faulty wiring inside.

The 115 V that you see between neutral and earth or active and earth is due to the EMI capacitors forming a voltage divider. Your multimeter must be very high impedance; usually you see 90-100 V because the multimeter load is significant against the medium-high impedance of the EMI capacitors. Any RCD/GFCI after the inverter likely won't work like this, which is the big safety concern.

I would check that your wiring from the inverter's earth terminals (AC-in or AC-out earth) to the distribution board's earth is good.

If you happen to have a very old model that doesn't have the automatic grounding of AC-out when in battery mode, then you will indeed have to arrange some external relay. But it has to know when the inverter is in line mode or not. Does your machine have setting 38, grounding box enable? If so, you can set it up so that the "clean contact" can drive your external relay at just the right time (when the inverter is in battery mode).

Thank you Coulomb for your insightful reply!

 

I only bought my inverter a month or so ago, so it *should* be quite new...

The earth wiring seems to be all good after I double checked it with my multimeter.

 

When I power everything down, I get >100MΩ (yes mega, not milli) between earth and neutral and also between earth and live on the output of the inverter. Does this mean that something in my inverter is broken?

My machine does not have setting 38. I have checked the manual, which states that the dry contact is operated depending on the battery voltages defined in Program settings 12 & 13. Probably useful when using lead acid batteries, but useless in my scenario.

 

Is there a firmware that I would be able to flash onto my inverter to get to setting 38?

 

Otherwise I guess I'll have to build an op-amp circuit to measure the voltage between earth and output neutral. I can then use this op-amp circuit to energise the N to E bonding relay. If there is a large enough voltage between E and N, the relay will bond the two together, while it will disconnect the two when the inverter is in bypass mode and there is almost no difference between E and N.

 

Update: I have fitted a relay to bond the live and neutral. The relay is operated by Eskom mains power, so if there is power the relay breaks the bond and when there is no power the bond is re-engaged. The only drawback is that the output is still floating for about 10 seconds when mains has just come online. This is however way better than it floating all the time! Pity my inverter cant signal it without any dodgy modifications.

Edited March 23, 20224 yr by Wiggly Electron