ESS with Fronius, problems with overload and AC2

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bulraydin asked Jan 15, '21

ESS with Fronius, problems with overload and AC2

Following setup : 3 x Multiplus 48/5000 II, 1x MPPT 250/100 , 1x Fronius Symo 12.5 and 2 x BYD 15.4

AC1 out and AC2 out are separated.

AC1 loads sum up to 10kW and AC2 loads sum up to 10kW max

We have been observing 2 problems :

1. Approximately every 7 or 10 days we encounter this problem. During daylight, while Fronius is producing 2-3 kW, and system is working with reasonably low loads under ESS batterylife, suddenly one of the phases gives overload alarm and system shuts down. We ask the household, they say nothing of high power was being drawn that moment.

2. During ESS, now and then AC2 output is disabled, although there is grid on the mains.

Following my observations :

This overload situation or AC2 output disabling never happens when system is in passthru mode.

Overload situation seems to happen while Fronius is producing, could it be that due to sudden clouds, the pv production makes a dip and then the multiplus try to invert that missing power ? which is then too sudden and causes overload ?

AC2 disabling : could it be that during ESS AC1 and AC2 are being regarded as one output and as soon as the total load of AC1 + AC2 goes higher than 15kVA AC2 is being dropped ?

What are your suggestions to debug these problems ?

ESS Fronius

2 |3000

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Answer 1 · 2021-01-17T09:48:02Z

Paul B answered · Jan 17, 2021 at 09:48 AM

1 x is the DC voltage also rising by chance

2 x check to make sure that frequency shift is working correctly and that the PV inverters are deratting correctly when the batteries are FULL and mains is off (refer item 1)

3. re the AC 2 out dropping are you using the general flag assistant and is it set correctly

4. if the above is of no help then please supply a screen shot of all the assistant settings

5. I presume you have a venus GX unit as its not shown in the items list, is there anything else thats connected.

6. is everything on the latest Fw versions

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bulraydin commented · Jan 19, 2021 at 01:08 PM

hi Paul

thanks for your comments.

1. DC voltage is not changing much at that moment. Also the resolution of VRM portal is just 1 minute, hence we never could catch how this overload was happening.

2. Frequency shift is working fine. We only use the Assistant ESS. Inside this Assistant you can set the PV inverter details.

3. As mentioned in 2. we don't use any other assistant. Hence there is no special programming for AC2 out. We really don't understand why AC2 is dropping out while the grid is available.

4. the settings are really usual setting for ESS

5. The system is controlled over Cerbo GX, to this everything is connected (Fronius, MPPT Charger, BYD batteries)

6. Yes everything is latest FW.

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Answer 2 · 2021-01-17T13:53:36Z

thomasw-1 answered · Jan 17, 2021 at 01:53 PM

Update:
Please have a look to following thread. It seems to have a similar issue like you.

Hi @bulraydin,
Yesterday I disconnected a system from gid in order to bypass Fronius throttling.
When I looked later to the system I observed following interesting situation.

Fronius Symo produced about 3.000W (1000W per phase) and 4.200W have been absorbed on L3 of AC-Out 1. On phases 1 and 2 the consumption was at ~1.000W. At that moment the MultiPlus-II 48/5000/70-50 on L3 already indicated overload by LED, although only ~3.000W had to be generated by that MultiPlus (5.000W actually expected below 25°C).

Since the device should be capable to cover 5.000W, I am really irritated. In my case at least the system didn't shut down. But at least it could explain, that system decides to shut down far quicker than it actually should do.
Firmware bug?

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marekp commented · Jan 17, 2021 at 02:08 PM

Fronius Symo produced about 3.000W (1000W per phase) and 4.200W have 
been absorbed on L3 of AC-Out 1. On phases 1 and 2 the consumption was 
at ~1.000W. At that moment the MultiPlus-II 48/5000/70-50 on L3 already 
indicated overload by LED, although only ~3.000W had to be generated by 
that MultiPlus (5.000W actually expected below 25°C)

For MP-II 48/5000, 4000W is expected at 25C not 5000W.

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screen-shot-2021-01-17-at-30701-pm.png (38.1 KiB)

Ingo commented · Jan 17, 2021 at 02:08 PM

Just a quick note on the expected load carrying capacity - see datasheet excerpt below.

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1610892388511.png (41.8 KiB)

bulraydin commented · Jan 19, 2021 at 01:18 PM

Hi @ThomasW. indeed, this thread could help me with the sporadic overloads. My firmware is 470, I thought online over vrm I could update always to the latest. But seems victron professional still needs to be checked.

However would this solve also the sporadic drop out of AC2 output ? From your last thread I know, we have almost exactly the same system (3xmultiplus, byd and mppt and fronius) Have you also seperated the loads to AC1 out and AC2 out ?

As mentioned this AC2 out dropouts occur only while ESS is running on a mixed mode ( batteries, solar grid together )

We just need to know how this ESS algorithm really works. I guess it sees AC1 and AC2 as common and limits the power to these loads as inverter power. As soon as load is higher then invert power it drops out the AC2 ?

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thomasw-1 commented · Feb 18, 2021 at 09:56 PM

Please consider that firmware 481 fixed following issue:

False overloads proved still to be possible.
A cause for this has been found and a solution is implemented to prevent this.

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