SOC calculation worse with latest Multiplus firmware

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pmikep asked Feb 25, '21

SOC calculation worse with latest Multiplus firmware

First, let me say that I understand that, for my setup, the Multiplus's calculation of SOC will inherently be incorrect.

(Right now I have my battery bank being charged by both my Mutliplus and occasionally by my SmartSolar MPPT. So the Multiplus cannot see the current being fed to the batteries by the MPPT.)

Still, the SOC calculation was better with the firmware immediately prior to v481 that is now.

And I think it can be "hacked" to do better, as below.

Consider the following two screen shots, taken at two parts of the day.

This first shows the battery voltage is 26.56V and the SOC is 57%.

Now, as the day progressed, with solar charging, the battery voltage has increased to 26.82V. But the SOC has decreased to 31%!

I know that this incorrect SOC calculation is because the Multiplus is (apparently) looking at current only, and has seen 7 to 8 Amps leaving the battery all day, but is not seeing current coming in from my MPPT.

But as I said above, the previous firmware of the Multiplus handled this situation better.

Might I suggest a software hack, that when the battery voltage increases, the SOC calculation be prevented from displaying lower? That would solve the false low SOC reading in this case.

MultiPlus Quattro Inverter Charger SOC

before.jpg (68.1 KiB)

after.jpg (68.6 KiB)

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Answer 1 · 2021-02-25T06:11:58Z

trip-tracks answered · Feb 25, 2021 at 06:11 AM

A Battery Monitor such as the SmartShunt or BMV-7xx series would sort this issue without a "hack", as you suggest.

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pmikep commented · Feb 25, 2021 at 06:23 AM

Yes, I understand. My point was more along the lines of "The SOC calculation seemed to be better in the previous firmware. Maybe they can put some of that back."

(And, too, not stated in my OP, up until this latest firmware, I was using SOC for AC Input control (having it charge my batteries when SOC went below 65%), which worked fine a few weeks ago. But not now.

And even if I bought a BMV-7xx, it seems it would take more wiring and money to get it to talk to the Multiplus for SOC info.

For now, I'm using voltage to trigger AC Input control.)

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trip-tracks pmikep commented · Feb 25, 2021 at 08:10 AM

You didn't say what type of batteries you have, but with Lithium batteries being so popular, it is impossible to determine SOC based on voltage unless at the upper or lower knee.
A battery monitor is your only solution, I am afraid.
Victron recommend a battery monitor if you have anything other than AC loads from the inverter.

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pmikep trip-tracks commented · Feb 25, 2021 at 03:16 PM

Yeah, BB LiFePO4's.

As another idea - if Victron isn't doing it already - it seems to me that there should be a BT peer-to-peer network for all these different components, so that a user can buy a SmartSolar MPPT, and a SmartShunt, and the BT dongle for the Multiplus, and all of them can talk to each other over BT (say, for SOC calculation). This way the user doesn't have to buy extra hardware and doesn't have to physically connect data wires to each component.

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Answer 2 · 2021-02-25T08:15:37Z

seb71 answered · Feb 25, 2021 at 08:15 AM

Right now I have my battery bank being charged by both my Mutliplus and occasionally by my SmartSolar MPPT. So the Multiplus cannot see the current being fed to the batteries by the MPPT.

If you only have a Multiplus and a solar charger, this is always the case. Does not matter what firmware you have on Multiplus.

Probably before the firmware upgarde you had much less energy from the Sun (winter time), so the SOC estimated by the Multiplus was more accurate because the Multiplus was doing most of the charging, too.

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pmikep commented · Feb 25, 2021 at 03:11 PM

Perhaps. But the time difference between firmwares was two weeks. And it seemed to me that the SOC didn't decrease during the day while the MPPT was charging.

It occurred to me this morning that the All-In-One is going to have this same problem, since it is a Multiplus and a MPPT both in one box.

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Answer 3 · 2021-02-25T18:49:02Z

Matthias Lange - DE answered · Feb 25, 2021 at 06:49 PM

Did you checked all settings after the FW update?
A FW update usually reset all settings to default.

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pmikep commented · Feb 25, 2021 at 08:27 PM

Yes.

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