AC coupling voltage spike

DIY
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1

Hi,

I have an offgrid Victron Multiplus 5Kw, fronis inverter 5Kw (in MG50 mode), MPPT RS 450/200, 30kwh 48v lithium battteries with pylontech BMS

The problem is that when the battery is fully charged and a big load (toaster) disconnects suddenly the voltage surges up to 60v momentarily throwing a battery overvoltage error on the cerbo.

I decreased the fequency values in ESS slightly, but it still uses the AC coupling before the DC coupling.

Should I just keep decreasing the fequency values in ESS until DC coupling takes priority or is there a better way to make big loads draw from the DC side when at 100% charge?

2

Is the fronius set up correctly?
If you are offgrid you should be using pv inverter support not ess.

3

Sorry you are right its not ESS it is using PV assistant.

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As far as setting up the fronius I used the following instructions, there wasnt much to do except update to latest firmware and switch it to MG50 mode.

1.3 Setting up the Fronius with Setup MG50/MG60

When not pre-ordered with a MicroGrid setup, follow these steps:

  1. Make sure that the Fronius PV inverter is updated to at least the firmware version mentioned above. See Inverter list above.

  2. After making the inverter operational according to the manual, select the language and after this the country specific setup.

  3. Here choose MG50 or MG60 depending on the system frequency.

  4. Ready to start up.

4

And it does show MG50 on the fronius console screen.

5

You still need to do the dno settings here.
Particularly this one…

In the same menu, set Sunspec Model Type to int + SF

Does the Fronius connect to GX correctly?

I found the stock settings work ok for my fronius offgrid.

6

I’m curius why the DNO settings requirements would be listed in the AC-coupled PV with Fronius PV Inverters [Victron Energy] document as something that needs to be done for on-grid ESS design installation manual but not mentioned in off-grid insructions. I will give that a go - Thanks.

Yes Fronius is using wifi and is seen correctly in GX

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7

I’ve made the changes to the fronius

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8

now its displaying the firmware version in the GX!!! Thats an improvment, thanks.

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9

Yes, it is important there is the full communication to the system.
Change your controlling priorities as well to modbus being the priority.

10

I’m still getting the error messages that happens when the batteries are 100% and a high power device is instantly switched off like a toaster popping up.
In this instance all the power is coming directly from either the RS or the fronius and they cant respond to the sudden reduction of load quick enough and throws an error.

11

Are you batteries when they are 100% at absorption voltage or float?

Have you programmed them to 52v and 51v as in the guide?
Using the pv inverter assistant instead of ess is preferable when offgrid.

12

Thanks LX,

Which guide are you referring to? I’m using PV intereter assistant.
https://www.victronenergy.com/live/ac_coupling:fronius
I looked through this guide and I cant see anything about programing voltage to 51v and 52v.
Pease let me know.

13

I was referring to the inverter programming