Multiplus 2 with Victron SmartSolar MPPT - incorrect SOC

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offgridpowerwestoz asked Sep 22, '20

Multiplus 2 with Victron SmartSolar MPPT - incorrect SOC

The State of Charge is displayed incorrectly on the Colour Control GX display and it's showing a drifting pattern towards 0%. A the moment the SOC reaches 8% during the day and goes down to 0% over night, even though the batteries are fully charged up.

We have the following components in an off-grid system we installed for our client:

1 x Victron SmartSolar MPPT 150/70-Tr

1 x Victron Multiplus-II 48V/3000VA 35-32 inverter charger

1 x Victron Colour Control GX

4 x Deep Cycle AGM Battery 12V 200Ah C20

12 x 330W solar panels

The system is connected to the internet via VRM.

The MPPT charge controller charges the batteries up, by 8.30-9am in the morning and then goes to float for most of the day.

Why is the SOC displayed incorrectly?

Technical support from the distributors suggested installing the BMV or the Smart Shunt to fix the issue. However, the Victron manual says this is not required. The site is far away from our office.

Can anyone point me in the right direction how to fix this issue?

I've read the other threads with similar issues but the solution proposed didn't work for me.

I really appreciate your advice.

Here are the settings from VE Configure on the Multiplus II:

Here the SOC graphs from the last 30 days:

Here the voltage, current and MPPT status from today:

Multiplus-II MPPT SmartSolar CCGX Color Control SOC

settings-df-last.jpg (55.6 KiB)

settings-df-last-2.jpg (62.7 KiB)

soc-pattern.jpg (27.1 KiB)

voltage-and-current.jpg (48.9 KiB)

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Answer 1 · 2020-09-22T13:13:34Z

JohnC answered · Sep 22, 2020 at 01:13 PM

Hi @OffgridPowerWestOz

What I think is happening here is that the Multi is seeing a slightly higher V than the mppt is, so the Multi isn't registering an Absorb state. It will still register a rise in SOC, but once that reaches 95% it will stop doing that, and is awaiting to see it's own Absorb V satisfied before it continues. So in effect you'll lose 5% per day. And your graph shows close to that.

A quick fix is to drop the Absorb setting in the Multi to where it can see it. I'd go down say 0.5V to test, then fine-tune it later.

Re the settings. With the low drawdown shown, 95% might be ok, but the 85% default is likely better for heavier use. You may find it pushing early to 100%, and whilst the client may well like to see that, it's not really right.

Same goes for the 1.00 Charge Efficiency. That's unrealistic, and in reality will be closer to 0.85. Or even less.

To get the devices looking at exactly the same V, you could invoke DVCC in the CCGX. Even then I'd set the Multi Absorb maybe 0.1V below that set in the mppt. That's SVS, and then there's STS, so the mppt can use the Multi's Temp probe to compensate V settings over the whole day, equivalent to what the Multi would do.
https://www.victronenergy.com/live/ccgx:start#dvcc_-_distributed_voltage_and_current_control

The BMV and Smartshunt are far more precise devices. But they need tuning too for best results..

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offgridpowerwestoz commented · Sep 24, 2020 at 02:21 AM

The issue still persists, even after changing all those values. Any more ideas how to fix this (other than installing a smart shunt or BMV)? Surely the Multiplus can determine the SOC better than this? Just not sure what I'm missing in the settings.

Current settings on the Multiplus are:

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soc-pattern-2.jpg (27.3 KiB)

1600913969005.png (75.9 KiB)

changed-settings-v2-b.jpg (64.0 KiB)

JohnC ♦ offgridpowerwestoz commented · Sep 24, 2020 at 11:26 AM

Ok. Questions and maybe things to try..

On ~28th Aug there was a spike upwards. Perhaps a generator charging via the Multi, has reached Absorb and reset to 95% as it should. Then finished off at 100%?
If so, can you home-in on that occurrence and try to relate it to the other parameters the Multi is seeing, particularly V. Also what the mppt was seeing at that Abs level. If you post any more graphs, zoom in to just a single day, even less.

You could even try to simulate this (again?). Shouldn't take long with a generator if the batts are charged.

Are there any loads other than the Multi, like dc loads?

What firmware in the kit? Particularly the Multi.

@OffgridPowerWestOz

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Answer 2 · 2020-09-23T02:46:03Z

offgridpowerwestoz answered · Sep 23, 2020 at 02:46 AM

Hi John, thank you for the quick reply. I've just changed the settings to this as per suggestions... Got battery efficiency value from the battery supplier. Let's see how it goes. It will take another day I presume before we can see the effects. Also checked up on the DVCC settings, they were already set as per the recommendations. Thanks again for your help.

changed-settings-v2.jpg (56.5 KiB)

changed-settings-v2-b.jpg (64.0 KiB)

dvcc.jpg (38.4 KiB)

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