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conradjdw avatar image
conradjdw asked

MultiPlus II SOC reading incorrect

Hi all, I have the MultiPlus 2 with 7 AKKUTECH (http://www.akku-tech.com/en/product-details-4.html) batteries. The Multi is connected with VE.CAN - CAN type-b to the battery CAN port. (The batteries all all connected together via RS485 jumper cables) The Multi can see all 7 modules on the GX.

I have selected to have the SOC read from the Battery CAN.

An example of an issue i have now: If I log into the battery or just observe the battery LCD screen, it shows a SOC of 85%, but the SOC displayed on VRM is say 100%.

Sometimes its correct (shows the primary battery SOC), other times its just way off. I want to resolve this discrepancy.


How do i solve this? Other than it being annoying in VRM, im worried that the incorrect values may prematurely shut down the invertor or prematurely stop charging - leaving me with quite an inefficient system.

SOC
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5 Answers
JohnC avatar image
JohnC answered ·

@conradjdw

Make sure the Multi's own battery monitor is disabled.

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conradjdw avatar image conradjdw commented ·
I have done this now, but it did not seem to make any difference. The reading that i saw in the VE Config before I turned it off appears to be a kind of average of all the SOC from the battery array. (ranging from 85% to 100%)
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nickdb avatar image nickdb ♦♦ conradjdw commented ·
For unsupported batteries it is best to ask the manufacturer for how to configure it for victron.

All you can do is select the bms as the monitor in the gx setup, assuming you can see it from the gx.

The rest you will need to ask them for support directly.

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conradjdw avatar image conradjdw nickdb ♦♦ commented ·

I have adopted this solution with the house. AKKUTECH support is absolute zero, brick wall, nothing! The local distributors have tried to help, but cant help, they just don't know either.

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conradjdw avatar image conradjdw commented ·

Something I am seeing is that in the Remote Console (of the GX), I can see the battery section is reading the Sate of Charge as 100%... so its just using what its fed in from the CAN (i suppose that's what i asked it to do).

So now is guess the question is why is the CAN feeding it a SOC of 100% when logging in directly into the battery (or observing the LCD) is showing the correct SOC?

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conradjdw avatar image conradjdw conradjdw commented ·

1686403886528.pngThis is NOT the SOC on the (primary) battery LCD. One of them sure, but not all 7.

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1686403886528.png (24.8 KiB)
nickdb avatar image nickdb ♦♦ conradjdw commented ·
They seem to be emulating BYD.

It appears that either the battery isn’t configured to communicate properly to victron or they aren’t properly compatible.

There will be little victron can help with here if it is reporting incorrectly.

You have verified that under the GX settings, system settings, that the monitor is set to the CAN battery and DVCC has been enabled.

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conradjdw avatar image conradjdw nickdb ♦♦ commented ·
Correct: battery monitoring is set to CAN, and DVCC is on.


Ok, so if the battery bms is total junk… what can I do then? Could I manually manage the battery charge with a shunt and a BMV?

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nickdb avatar image nickdb ♦♦ conradjdw commented ·
When all else fails a shunt is the best plan B.
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Alexandra avatar image
Alexandra answered ·

@conradjdw

Interesting, usually a pack(like BYD) reports the lowest battery as the system SOC. It seems the manufacturer of yiurs has decided opposite.

The real question you should be asking is why is the SOC of the batteries so different? Do they have an issue with determining SOC, some trigger to early when current drops during charging.

How is your bank wired up?

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conradjdw avatar image conradjdw commented ·

Interesting, usually a pack(like BYD) reports the lowest battery as the system SOC. It seems the manufacturer of yiurs has decided opposite.

Yes, this appears to be one of the main problems. Its very strange.


If i was to opt of physically changing out the BMS, what board would you recommend?

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nickdb avatar image nickdb ♦♦ conradjdw commented ·

From the compatibility list:

List of 3rd party BMSes that are known to work with Victron (but not tested by Victron!):

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conradjdw avatar image
conradjdw answered ·

@Alexandra yea I’m not impressed by the BMS at all.

I have all 7 batteries connected to a DC combiner box, attached to that is the Multi and the Mppt, with a GX. It’s pretty standard stuff, and everything else works fine. It just this very strange SOC.

Let’s say the bms it a total loss, before I throw out 7 (what seem to be brand new) batteries, could I use a shunt based system rather? Then the batteries just become a basic storage.

As you can imagine the SOC of each battery gets wildly different at times. I have to do a long charge-up every so often. Would a shunt (or a shunt per battery) solve this?

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Alexandra avatar image Alexandra ♦ commented ·

@conradjdw

I would switch to a shunt definitely.

Nice feature with the shunt will be time to go to your discharge floor of 90%, its a neat feature.

And dont stress about it. You obviously have a correcy sized bank, even the discharge current would not be an issue. So comms aren't necessary and capacity is capacity.

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conradjdw avatar image
conradjdw answered ·

Ok, so it seems clear the shunt is the way forward. I’ll ask my installer to add it.

Just some questions on this: I’m assuming that one shunt would be fine for all 7 batteries at the common negative, right?

Do they cater for LifePo4? They don’t seem to be based on a battery chemistry. Or are they settings?

I have noticed the SOC differ drastically from one battery to the other. The shut just provides the SOC, for the entire bank, would this also solve the imbalance? I assume the correct amount of charge time should solve the imbalance, right?

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Alexandra avatar image Alexandra ♦ commented ·
@conradjdw

No the standard can pass 500A over it no problem

The peukerts setting is the main change between lead and lifepo4.

The shunt will sync to 100% soc only when charged voltage is met and the whole bank is drawing under a certain (settable) amperage. Theoretically if balancing is an issue then the system would need to be set for a longer absorption time.

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conradjdw avatar image conradjdw Alexandra ♦ commented ·
Will add the shunt and provide feedback, thanks
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conradjdw avatar image conradjdw Alexandra ♦ commented ·

Theoretically if balancing is an issue then the system would need to be set for a longer absorption time.

On closer inspection of the battery balance problem it appears that their voltage is the same across all 7 batteries (52.6v), but the SOC varies from between 50% and 99.6%. If i'm not mistaken this is a characteristic of the LifePo4 charge/discharge curve.

Seems like i need to sync them up with a full charge up and long absorption.


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Alexandra avatar image Alexandra ♦ conradjdw commented ·
It happens, i have installed a few brands now that have SOC issues. I guess they havent quite worked out the firmware. A longer absorption helped. But the shunt was the best move on the systems.
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conradjdw avatar image
conradjdw answered ·

Some feedback from the field:

So it turns out the underlying problem was that the batteries had different parameter settings on some of them. One had its overvoltage alarm on 54v and its fully charged voltage setting at 52v, so this is why i was getting strange SOC readings, and over voltage errors on the GX. So after a bit of hacking around with PbmsTools.exe and having to guess the admin password, I eventually reset all the parameters on all the batteries! Yay

With regards to the Shunt. I have installed it, and changed over to using it as the primary battery monitor reading for the GX and to show in the UI. I will need to keep an eye on it for the next few days to make sure it tracks with the (now correct) SOC of the battery array.

More to follow.

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