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roem avatar image
roem asked

ESS mode keep batteries charged is discharging batteries during feed in

I have a grid-tied system intended as back-up system including excess solar feed in into grid. Some particulars:

Solar panels 2,4 kwP

Smartsolar MPPT 150-100

Multigrid II 48/3000/35/32 230V

ColorControl GX

4x12V-136Ah lead acid batteries (third party).

ESS is applicable with mode "keep batteries charged" and "feed-in exces solarcharger power". Also absorption voltage and float voltage according manufacturer's specs.


This is working well except that I noted that during daytime (solar available; inverted to 230V and used for load and feed-in) the batteries are being discharged in small amounts as well. It looks like the more solar inverted (i.e. fan on multigrid) the higher the discharge rate of the batteries will be (max approx 100W). The result is that at the end of the day SOC of the batteries has been lowered and overnight it is being kept steady (including floatvoltage is maintained). So each day the SOC of the batteries is lower (approx 7-8%). For this I have two (2) questions:


1) How are the batteries supposed to be charged again? I assume "keep batteries charged" means on or up to SOC 100% (for back-up reasons).


2) Each day my batteries have lower SOC but the voltage is steady floatvoltage. How does this effect the start of the charge-sequence as according to manual switch float-to-bulk will be at 1.3V below float voltage? And eventually will it recognise the dynamic cut-off as float voltage is kept continious?


At this moment the only option I know is to reset the system in order to start Multigrid in bulk. For now this is okay to reset the system once every couple of days. But when I leave home for longer periods and I am not able to reset?


I would appreciate some help and/or clarification with this. Thanks in advance.



MultiPlus Quattro Inverter ChargerESS
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5 Answers
pracman avatar image
pracman answered ·

Have you set up scheduled charging in the ESS? I have two, one for off peak power and another during Solar PV. My two batteries (ZBM2 Flow) charge during solar PV and off peak power exactly as scheduled.


Disclaimer-I do not have nor pretend to understand lead acid batteries best interests.

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roem avatar image
roem answered ·

In ESS mode "keep batteries charged" there is no option for scheduled charging. Only in mode "battery life" there is. I have tried to work around and used battery life with SOC set at 100% and scheduled charging. Problem is that it blocked the feed in. This is apparently happening when battery falls below 100%.

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pracman avatar image
pracman answered ·

I usually have min SOC at 40% or so. I wonder if you used "battery life" and tried 80% SOC and set a 24 or less scheduled charge if this might meet your needs? I can get almost 100% is SBS mode in my flow batteries which gives me 20Kwh or so of U.P.S. As mentioned I am not a expert on maintenance needs of lead batteries so excuse me if I am off track.

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roem avatar image
roem answered ·

Firstly, I appreciate you're trying to think along with me. For your information my system has been installed a little over a year ago. It originally was intended as back-up system, but it took about one year before we got permission to feed-in into the grid. So the first year we used the system in mode "battery life" with SOC set at 60%. (Lead Acid batteries are recommended not to be used SoC lower then 50%). What I noted over this period of time that de battery-efficiency was only 50%. I tested with higher SoC and that makes the battery-efficiency even worse.

When I got the permission for feed-in it makes it financially more feasable to feed-in maximum into the grid and buy-back whenever I need the power. Therefore I changed mode to "keep batteries charged". Another advantage is that my back-up is (or at least should be) at maximum all the time. In this setting I noted what I wrote in my question.

I do not know if this "discharging" is happening during mode "battery-life" as well. I never noted it before. But battery-life did charge my batteries every day so it was hard to verify. With feed-in into the grid another aspect changed and that is that the inverter is inverting continiously at about 80% capacity rate during the day (as opposed to battery-life without feed-in which only inverted the loads needed).

So I can always go back to the situation I had before (battery-life and SoC 60%) and accept the financial consequences as is. But still my question remains that I expect with "mode keep batteries charged" means keep batteries full (SoC 100%) at all times. And apparently this is not the case in my system.


6 comments
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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi @ROEM

How do you know there is energy coming from the batteries?

What does your system consist of? how is PV connected? what kind of battery monitor?

Can you post graphs with battery voltage / current?


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roem avatar image roem Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi Daniël,

Our system is 3x3 275Wp solar panels connected to Smartsolar 150-100 MC4. On battery DC side connected to Lynx distributor 1000DC. From Lynx busbar one to Batteries in series (4x12V-136Ah) and one to Multigrid II 48/3000/35/32 230V. Color Control GX installed. No BMV but SoC tracking in the Multi.

See graphs. Note I selected Voltage and Ampere for 1 day for better view. I included Battery Watts graph in which you can see more watts are taken out of battery than vv.

Please note that feb 17th I checked batteries with density meter as well and results are consistent with graphs.

In case you need more info please let me know.

Thanks.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ roem commented ·

seeing the voltage graph, I don't think the battery is discharged at all.

SOC calculations seem off, this can be tweaked in the Multi's settings.

What I'm missing here is a DC graph also for a week, I wonder if there is any repeated Bulk charge. what are the charging settings in the Multi?

Please remember that the DC current is a calculated value here, the MPPT's current and Multi's current are subtracted to come to these values.

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roem avatar image roem Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Please find the DC graph for same period. DC Voltage is kept steady over this period at floatvoltage setting. Bulk/Absorption voltage is 59.4 V. Please note the bulk charge at feb 16th was initiated by myself by resetting the system.

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offgridvoltage avatar image
offgridvoltage answered ·

Hi Roem….what was ur final solution to this ? Did you figure out why the battery was discharging whilst in ‘Keep Battery’s Charged’ mode ?

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