Question about EM540 and feed-in with negative grid set point

Q&A and troubleshooting
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1

Hello, I have three questions

  1. Is it worth setting the EM540 baud rate to higher than the default (9,6kbps) or the cerbo supports only (9,6kbps) ?

  2. Is it normal that the EM540 meter has bad data (consumption, export and import to the grid) on the VRM portal?

  3. And another question, when I have set the grid point to -350W(permanently) and still at the end of the day I have a grid import of about 150-300W. Is it normal?

Setup:

EM540 (via usb rs485 to cerbo gx), cerbo gx, 3x MP II 48/5000/70, pylontech US5000 battery, ESS mode without battery life, all latest firmware

2

Hi

Higher baud rate is not possible, i have a EM540 and no problems with data, is you connection ok?

You can have grid power usage with -350 negative value, ESS will try to balance at -350w but if you have high loads it can draw from grid

Also do you have multiple US5000 batteries or just one?

3

Yes,connection is correct and I have 4x us5000
With the high load, you’re probably right that it do not have time to regulate so it takes something from the grid.

I use the data also in Loxone via modbus TCP and if I compare for example yesterday, I have on VRM export 19,8 kWh, import 0,3 kWh and self consumption 34,9 kWh and in Loxone was export 33,3 kWh, import 153 Wh and self consumption 27,3 kWh. Solar power production was 59.8 kWh on the VRM and 60.6 kWh in loxone, so I understand some small difference, ± 1kWh or some rounding in Watt , but difference in export data and self consuming data seems too big a difference. Maybe it is normal, but I have no way to compare it to another installation. Data in loxone seems more real to me.
When I look at the live view in loxone, I see the same values as on the VRM (but faster because I read them every second) I know the VRM is a bit slower, but it is weird to me that the values would be so different at the end of the day.

4

Have / can you check the numbers against that of the energy supplier’s readings? VRM also only logs data at 1min intervals.

5

Yes, but only monthly and it was ± a few watts same, that is why I think the stats I read into loxone are more realistic, but before EM540 I was using ET340 and the stats were the same with VRM and loxone ±1kwh in exports and ± W in others stats, but after switching to EM540 the VRM data is mainly wrong in exports and self consumption, so maybe it is because as you say the portal only reads in minute intervals.
Never mind, I wanted to know if the problem is only on my side or if it is normal with faster energymeters

6

Sure. Also worth noting these possible differences. Q8: What’s the difference between ET340 and EM540 in 3-phase systems?**

These meters have a different way of calculating the total of energy imported and exported.

In the ET340, the energy imported and exported is counted at each individual phase and then the Total is provided from the sum of those values.

In the EM540, the energy imported and exported is counted as a total power, with net differential readings from each phase cancelling each other out.

Which Energy Meter is most suitable depends on the measuring configuration in your country. It is most common in Austria and Germany for example to only be billed for the total in a 3-phase system. So it is more accurate to use an EM540 to match the billing.

So if you are exporting from one phase and importing from another phase after the energy meter, but before the billing meter, then you will not be charged for this, and the meter should not count it as an import and an export.

This is also how Victron’s phase compensation feature works, to make the most of the cost savings for an ESS system when there is a differential in generation and load across different phases.