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How to set it up to avoid back to grid behavior?


Marcel Cerdan
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Hey guys,

I'd like to avoid my system to go back to grid when batteries voltage dips for just a few seconds under the Back To Grid voltage setting.

Here is my system:

2x Mecer Inverters 5kVA/4kW SOL-I-AX-5M in parallels.

24x PV Canadian Solar 270W C26K-270P-FG

16x 12v AGM battery OmniPower OPR 240-12

1x Victron BMV 712

1x ICC Pi

I attached the inverter configuration.

It's running smoothly most of the time and we barely need to draw from the grid. Only when we have several cloudy days in a row.

However, I'm struggling with one issue. While the SOC remains above 90%, the voltage is sometimes dropping under 48V for a few seconds, triggering the Back To Grid setup. A few seconds later, the voltage is back above 50V, hence the Back To Discharge setup at 50V and not 54V.

Is there a way to prevent the system from going back to the grid when the deep below the triggering voltage is so short?

Cheers!

 

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28 minutes ago, Marcel Cerdan said:

I'd like to avoid my system to go back to grid when batteries voltage dips for just a few seconds under the Back To Grid voltage setting.

One solution is to use patched firmware version 73.00e with KettleKomp™. That feature compensates the battery voltage for presumed internal resistance before applying tests like "should I switch to utility mode considering this latest battery voltage reading". Also, if it does switch to utility (it's not perfect), the minimum time in utility mode is reduced from 10 minutes (factory firmware) to 2 minutes (patched firmware). I find that 2 minutes is a lot less aggravating.

What I mean by load compensation: if the measured battery voltage is 47.8 V and there is no load and no charging to speak of, then it's really 47.8 V. But if there is a 3000 W load, and the internal resistance is set at medium, then (for argument's sake) consider the battery voltage to be 48.8 V. At the highest level of compensation with the highest load, the battery voltage will be adjusted by 2.0 V. Similarly, if the measured battery voltage is 47.8 V, but the net current into the battery is say 50 A, then consider the battery voltage to be say 47.0 V. The idea is that a chunk of the sag or rise will be due to internal resistance of the battery, so let's adjust for it. Now, there are only four settings for internal resistance (plus a fifth option of zero compensation), and internal resistance varies with battery temperature and state of charge, so this is all very approximate. But it's way better than no compensation. There are displays for both the raw and compensated battery voltages on the LC Display. There is also a command to read the two values, in case you want to do something with it in a Pi or 'Duino.

You might want to wait to see what happens with the soon to be beta released patched firmware version 74.40e. This patched firmware has all the features of 73.00e, but is designed for PF1.0 models. Nevertheless, it has been shown to run on inverters like yours and mine (both PF0.8 models). But it may take a while for me to finish alpha testing (it went into my first inverter today, but I need fine weather for testing out in where the inverters are, and the forecast is for intermittent rain). Also, you may care to wait for some others to beta test first. Also, and I'm in this camp, you might be uneasy about a firmware update that turns your 4 kW machine into a 5 kW machine like magic.

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13 hours ago, Marcel Cerdan said:

I'm already running on 74.40 firmware. Does it means that we turned our 4kW machines into 5kW ones?

I suspect so. I'm reluctant to try it in my machine here for continued alpha testing.

Do you perhaps know that you've delivered significantly over 4 kW already, perhaps from logs? Did you perhaps also log temperature?

We know the inverter proper can take it,  since it's rated for 5 kVA; 5 kW is the same current when the load has a power factor of 1.0.

It's the DC-DC converter that I'm concerned about: especially the 16 MOSFETs (4 sets of 4 MOSFETs paralleled) on the battery side.

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@Coulomb

Hey! As you know from saving my ass of the error 90 a week ago or so, I'm on 74.40 for a while now. I'd say 2 months and a half now. Only because I was asked to install it by the local Mecer importer.

I use the ICC on Pi but I don't see load and temperature logs. Only graphs for the last 24 hours. If you know where to find them, I'm happy to extract them for you.

I can screenshot the graphs for a few days too at like noon every day.

I'm not sure we pushed the inverter above 4kW. We usually peak around 7/8kW on 2 parallels inverters.

Regarding firmware 73.00e, is it this one I found in the post on the AEVA Forum? http://forums.aeva.asn.au/viewtopic.php?p=70827#p70827

Cheers!

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3 hours ago, Marcel Cerdan said:

We usually peak around 7/8kW on 2 parallels inverters.

So then you haven't pushed either one past 4 kW, likely. As soon as I get mine paralleled, I might be able to do the same. But I'll probably drop down to 73.00e for safety as well.

 

3 hours ago, Marcel Cerdan said:

Regarding firmware 73.00e, is it this one I found in the post on the AEVA Forum? http://forums.aeva.asn.au/viewtopic.php?p=70827#p70827

Yes.

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