question

djdemond avatar image
djdemond asked

SoC why is it so flaky?

I have two installations both ESS grid-parallel battery systems both primarily time-shifting off-peak electricity to peak times. Each using multiplus II 48/5000/70 units.

2p16S configuration brand new EVE 230Ah LiFePO4 cells with Daly BMS 250 amp.

However, despite the nameplate capacity being 48V 460Ah for each pack, the actual performance varies considerably with temperature for example. As such I might get 300Ah before the SoC shows as low (I am using 25% SoC as ESS low limit) or I might get 350Ah.

I understand that voltage, on paper, is a more accurate measure of charge, than counting charge in and out (Ah) but under load, it is unreliable as it drops. So we use SoC whilst under load. However, it doesn't seem to be very intuitive or clever.

How is the battery pack in my MG5 LR EV managing itself without what I am having to do - the constant tweaking of the capacity in VEconfigure or the ESS stop on SoC level.

I want to set the thing up and then forget about it.

Also, can someone explain what the adaptive charging in veconfigure is all about?

Multiplus-IIESSSOC
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3 Answers
snoobler avatar image
snoobler answered ·

2P16S of 230Ah cells is a 460Ah battery.

Does your DALY BMS report SoC?


Are you using the MP battery monitor? If so, how is it configured?


How is the charger configured?


What are your ESS assistant settings?


Voltage is NOT a more accurate measure of charge. It is actually pretty horrible and unreliable in an active system especially between 40 and 90% SoC. Current counting is MUCH more accurate.


Adaptive is intended for lead acid. For batteries that are only discharged a small amount, it runs an abbreviated absorption time. For you with LFP, you should be charging to 56.8V with a fixed absorption time of 30 minutes. Float set to 54V.


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djdemond avatar image
djdemond answered ·

Does your DALY BMS report SoC? Yes, it does, one installation for example the BMS shows 73% but VRM shows 57.5. I have tried setting various capacities using VEconfigure but they seldom track with much agreement.


Are you using the MP battery monitor? If so, how is it configured?

Yes I am

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How is the charger configured?

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What are your ESS assistant settings?

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Thank you for your help.


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4 comments
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Not sure if this can cause your problem but your sustain and cut-off voltages are super low for a 16S LiFePO4 setup.

For BYD (also 16S LiFePO4) the recommended settings are 50V sustain and 47V for all cut-off.

https://www.victronenergy.com/live/battery_compatibility:byd_b-box

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djdemond avatar image djdemond Matthias Lange - DE ♦ commented ·

1674999903145.png

Rarely get anywhere near these low voltages, but finding it would cut off under load via the dynamic values at fairly high voltage.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@DJDemonD All 3 values seem less than optimal.

gigo.png


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djdemond avatar image djdemond klim8skeptic ♦ commented ·
Thank you that was very helpful. What values would you recommend?
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Al avatar image
Al answered ·
If the Daly BMS reports SOC, is it selected as the battery monitor in system setup on the GX device?

The Multi Battery monitor is not accurate, you shouldn't need to use it with the DALY BMS, or bmv / smartshunt which would be much more accurate than the internal guessing of the multi SOC.

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djdemond avatar image djdemond commented ·
Thank you. No, it is not as presently the Daly BMS is not interfaced to the inverter/RPI venus OS at all.
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Al avatar image Al djdemond commented ·
So I guess you need the Daly interface board to get it to work in Venus, seems others have got the Daly BMS talking to GX's, or get a SmartShunt.
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