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Victron ESS mode keep batteries charged is discharging batteries during feed in


ROEM
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Hello,

 

I have some questions for which I have not found an answer/reply yet on the internet and victron community forum. I hope some of you can help me with the following:

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.

 

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6 hours ago, ROEM said:

So each day the SOC of the batteries is lower (approx 7-8%).

I suspect this "SOC creep" isn't real. First, look at the voltage. If the voltage is more or less stable around the configured float voltage (usually it will be slightly above it), then the answer is that the SOC is inaccurate and your system is in fact working just fine. I will get into that next.

Right, so on your hardware list I did not see a BMV (battery monitor), so I have to assume you use the SOC tracking in the Multi. If you look on VE.Configure, there is a battery charge efficiency value:

Selection_474.png.60dcdae7d872326bf47278b4aa0e45f0.png

If this is set too low, your SOC will tend to creep downwards. This is because for each 0.8 Ah that leaves the battery, the Multi needs to see 1Ah go back in before it will consider the battery full again. If your battery is more efficient than that, the battery will fill up before you get the extra 20% into it... and the SOC will reflect this. You will then see this southwards creep over a few days.

Simply tune this value upwards. But do check that the voltage is held. If the voltage is permanently held at float... then the issue is likely SOC creep and not an actual discharging battery.

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Hello Plonkster,

 

Thank you for your quick reply and explanation. This is what I was hoping for.

 

For your information: I am just a user (but with a little knowledge about electrical systems due to my merchant marine background). I already contacted my installer/suplier about this but no response from him. He also did not supply me with the tools (password etc) to look for myself inside VE Configue. I only have acces to the Color Control.

1 hour ago, plonkster said:

If the voltage is more or less stable around the configured float voltage (usually it will be slightly above it), then the answer is that the SOC is inaccurate and your system is in fact working just fine.

Yes, float voltage is stable.

 

1 hour ago, plonkster said:

so I have to assume you use the SOC tracking in the Multi

Correct.

 

1 hour ago, plonkster said:

If this is set too low, your SOC will tend to creep downwards. This is because for each 0.8 Ah that leaves the battery, the Multi needs to see 1Ah go back in before it will consider the battery full again. If your battery is more efficient than that, the battery will fill up before you get the extra 20% into it... and the SOC will reflect this. You will then see this southwards creep over a few days.

Simply tune this value upwards. But do check that the voltage is held. If the voltage is permanently held at float... then the issue is likely SOC creep and not an actual discharging battery.

 Ok. This is clear for me. I will contact my supplier again and request him to either check this setting or supply me with the password, so i can do it myself. Then I will monitor it a couple of days and let you know the outcome.

Thanks again

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15 hours ago, plonkster said:

What password would that be?

I was under the assumption that I need a password as per manual:

 

VictronConnect - VE.Bus Configuration guide

Edit this section # Warning

:⚠️:

The features described in this document are powerful tools. They are intended for use by Victron-trained Engineers, Installers and Dealers. Its usage must not be attempted by system Owners and Users.

Configuring our Inverter/chargers, such as Multis and Quattros, requires both training and experience.

Victron offers no direct support for un-trained individuals carrying-out configuration.

Settings are protected by a password. This password is provided with Victron training. Please contact your Victron Distributor for further information



 

I have had contact with installer/distributer now. I will let you know the outcome in due time.

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