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Rasmus Mikkelsen avatar image
Rasmus Mikkelsen asked

Not charging with full potential, exporting excess to grid

Hi all.

I have a 400ah 18650 48v battery. Using 250ah of them from 3.5v-4.0v. Charging to 55.6v and then the 0.4v is applied for excess solar to grid = 56v/14cells, 4.0v cell.

I have multiplus 2 48/5000, mppt 250/100, cerbo gx, 6.2kwp array.

This might be a simple question, but I have been wondering this for some time now. How come the victron gear wont charge the full potential to my batteries? Right now im exporting 1500w to grid, instead of filling up my battery as fast as possible?

Could be bad weather later in the day, which means I'm potentially missing out on some kwh's of storage for the evening/night.

Is this due to the 0.4v offset that is applied later on? I know it's not my bms (batrium) there is literally no reason for those 1500w beeing exported to grid right now :-)


Have a great day


screenshot-20230622-111920-vrm.jpg

ESS
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Alexandra avatar image Alexandra ♦ commented ·
@Rasmus Mikkelsen

Do you have battery life on or off?

What is your soc in case of grid faliure set at?

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Rasmus Mikkelsen avatar image
Rasmus Mikkelsen answered ·

Hi Alexandra

Min. SoC unless grid fails is set to 0%. Grid is very stable here, in Denmark inverter has to shut down if grid fails so no power on the lines.

I'm using "Optimized without battery life"

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Alexandra avatar image Alexandra ♦ commented ·

So technically the system has been told everything is excess ;)

And in DVCC there are no limits to the charge current? Does your bms communicate with the system and send CCL at all? Saying it is not the bms is not entirely correct since it is not an officially supported bms. I mean they work just not always as expected.

For export to happen the mppts will be outputing higher than the dc bus voltage to create potential. Otherwise there would be no movement.

You can check batt voltage vs dc bus voltage vs mppt batt terminal voltage

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Rasmus Mikkelsen avatar image Rasmus Mikkelsen Alexandra ♦ commented ·
Hi :-)


I'm not sure what you mean by system has been told everything is excess? If I set SoC limit to 10-20% doesnt that mean that in daily use of the system, it won't go below 10-20% so to always preserve 10-20% for backup when grid fails, which it doesn't. Well maybe once or twice a year during a storm.

Yea victron doesn't talk at all to batrium when grid feeding is enabled.

I did have a 70a limit on charge current in DVCC, have disabled this now. Also I have enabled "limit managed battery charge voltage" to 55.6v, maybe I shouldn't?

Yea bms sends ccl values and so on, but victron seems to not care for it hehe :-)

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Alexandra avatar image Alexandra ♦ Rasmus Mikkelsen commented ·
@Rasmus Mikkelsen
Yeah to feedback it has to ignore the battery telling it not to produce. It is mentioned in the ESS manual.

I meant that if the SOC is set low anything above that is technically excess. If i set a system to 90 % then it charges the system to that before considering production as excess.

If you don't want your battery to charge at all from grid maybe consider disabling the internal charger and set the sodlc in case of grid faliure higher then it will charge up higher on solar before export. Otherwise you will need to look at node red to control the battery charging and export balance.



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Rasmus Mikkelsen avatar image Rasmus Mikkelsen Alexandra ♦ commented ·
Thank you Alexandra. Yea what I'm after is a more aggressive charge curve really. But not sure it's possible. As n-dee stated below they are at 55.67v at the picture, and target is 55.6v with 0.4v offset. So its probably lowering the current as we are nearing 100% soc.

I might have a look at node red, thank you :-)

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n-dee avatar image
n-dee answered ·

Hi,

On the screenshot you've got 55,67v so it should go to zero then... (limit charge voltage to 55,6)

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Rasmus Mikkelsen avatar image Rasmus Mikkelsen commented ·
Hi, yea that is true. So it's because of the 0.4v offset that is confusing. Victron is then probably lowering current until 100% soc is reached, I just thought it was early it did lower the charge current around 70% SoC (ignoring my ccl from bms) but I think that is expected.
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