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BMV SMART-712 'Charged Voltage' & other settings for BYD B-PLUS 51.2V setup?

Hi from Christmas Island, with a couple of 100% off-grid, solar setups, each using a bank of 4 BYD B-PLUS 2.5. 2.56kWh, 51.2V, LFP Battery Units. I've installed a BMV SMART-712 shunt to hopefully give more accurate SOC, but am unsure on exact charge values I should dial in, really struggling to find answers online, and all businesses I've reached out to haven't really been able to give me any info. My system uses a Victron MultiPlus 48/3000 35-50 and a BlueSolar Charger MPPT 150/70.


Main question is - What should 'Charged voltage' be? I have it set to 56.8V (it was on 55.2V for ages which seems low and may explain why my batteries never seemed have much capacity). Some battery spec sheets (and written on battery itself) say "Working voltage: 44.8V-57.6V" but other spec sheets for the same battery say "Operating Voltage Range: 43.2~56.4V". If it's too low I worry i'm not getting full capacity from my battery (critical in my case), and if too high I worry I'll fry it somehow.


I'm more confident about the other settings, but would love some reassurance:

Discharge floor: 90% (I assume that's correct way around, not 10%)

Tail current: 4%

Charged detection time: 3m

Peukert exponent: 1.05

Charge efficiency factor: 98%? (I see mentions of only 'round trip efficiency 95-96%' on the battery specs though? Sounds low?)

Current threshold: 0.05A

Time-to-go averaging period: 3m


Thanks very much, I'd really appreciate some advice.

Chris

BMV Battery MonitorSOCBYD
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2 Answers
swell-lodge avatar image
swell-lodge answered ·

Thanks @Rob Duthie, however, I am familiar with that linked page, it does not provide any of the settings which the VRM SMART-712 is asking for, which is what I am looking for. And it also contradicts itself providing two different values for Absorption Voltage (which I assume is different again to the 'Charged voltage' value that the VRM calls for.


Half way down the page is suggested that using VEConfigure, some charge parameters could be set in the MultiPlus but points out that the values won't really be used anyway as it's normally overridden by the BMU but "However as a precaution it is advised to set these as suggested below." It then suggests Absorption Voltage 55.2V. Scroll down a few more paragraphs to the suggested MPPT charge settings, and then it says to use "Absorption Voltage: 56.5V". Which is correct? And How does Absorption voltage relate to 'Charged Voltage' anyway?


Any insights would be invaluable! It's doing my head in.


Thanks


Chris

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Rob Duthie answered ·

Hi

Use this link to setup the BYD batteries correctly.

Also you will need to use the VE Config to set them up via a Mk3 to USB interface as well.

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


Regards

Rob D

NZ

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Thanks @Rob Duthie, however, I am familiar with that linked page, it does not provide any of the settings which the VRM SMART-712 is asking for, which is what I am looking for. And it also contradicts itself providing two different values for Absorption Voltage (which I assume is different again to the 'Charged voltage' value that the VRM calls for.


Half way down the page is suggested that using VEConfigure, some charge parameters could be set in the MultiPlus but points out that the values won't really be used anyway as it's normally overridden by the BMU but "However as a precaution it is advised to set these as suggested below." It then suggests Absorption Voltage 55.2V. Scroll down a few more paragraphs to the suggested MPPT charge settings, and then it says to use "Absorption Voltage: 56.5V". Which is correct? And How does Absorption voltage relate to 'Charged Voltage' anyway?


Any insights would be invaluable! It's doing my head in.


Thanks


Chris

Hi


I would stick with those setting first anyway, as you don't won't to push it as the BMS will take over any and has full control over the charge and discharge anyway.

So it won't fry the batteries.

I have a similar system using Pylontech and there max voltage is 53.2 as they are Lithium phosphate they have a much lower voltage than Lithium manganese cobalt types.

Does you battery ever get to 100% when fully charged?

VEConfigure Charge Parameter Setting Battery type Lithium Charge curve Fixed Absorption voltage 55.2 V Float voltage 55 V Absorption time 1 Hr

Note: make sure to double check the float voltage after completing Assistants, and if necessary set it back to 55 V.

4.3 Inverter Settings

In the Inverter tab of VEConfigure

VEConfigure Inverter Parameter Setting DC input low shut-down 47V DC input low restart 51V DC input low pre-alarm* 51V


Regards

Rob D

NZ

Hi @Rob Duthie - thanks =)


Are you saying that 'charged voltage' i'm looking for to enter into the VRM SMART-712 battery monitor, that's not actually controlling the charge at all, it's just a voltage that the VRM waits to see for its own SOC calculations, and when it sees it, it will decide that SOC is 100% and will calibrate itself. That's it? So basically I could just watch and see what voltage the battery gets to one sunny day when the BMU has completely charged the battery, and just use that voltage as this 'charged voltage' 100% trigger for the VRM? If I set too high, VRM will never think it's full, set too low and it'll think it's full early but the BMU will actually keep charging further?


Thank you =)


Chris



Hi Chris


That's sort of sums it up.

Regards

Rob D

NZ

THANKS very much =)