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hebs avatar image
hebs asked

Node-Red BMS SOC %

Hello everyone, I hope you all have a great new year.


I have a question about the BMS SOC percentage figures in Node-Red: do any of you get this figure other than rounded to whole number percentages? Node-Red using the Victron nodes only shows SOC rounded to the nearest whole number. I am fairly sure that my BMS (Seplos Smart BMS - CANBUS) is sending the SOC to two decimal places. I would really like the extra granularity in Node Red.

Does anyone have any experience of this?

Do you all get SOC rounded to the nearest whole integer?


Thanks


BMSSOCNode-REDVE.Bus
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4 Answers
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

There are already nodes that send or receive from/to RS485 or Canbus and this can be a good starting point:

https://flows.nodered.org/node/node-red-contrib-socketcan

https://flows.nodered.org/node/node-red-contrib-serialport-rs485

If Seplos sends SoC in such a high resolution, it should be relatively easy to intercept and then use the data for your calculation.

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nickdb avatar image
nickdb answered ·

While the BMS may show a more granular SOC internally it may not send that information.

My BMS for example sends two different scales via CAN, the first is rounded up, the second is in 0.5% increments.

CANID 0x355 sends the SOC data.

The first two digits are SOC in % (MSB/LSB), the next two are SOH.

The final two are SOC again but more granular.

Your BMS may allow you to pull the data you want differently but via CAN it may be more limited.


screenshot-2023-01-02-at-110900.png


screenshot-2023-01-02-at-110900.png (14.5 KiB)
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nickdb avatar image
nickdb answered ·

That’s how it works. SOC is a derived metric, rather pointless tracking to decimal places when the BMS isn’t that accurate to start with.

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hebs avatar image hebs commented ·

I have edited my post - I accept that the BMS isn't that accurate but the granularity isn't pointless to me:


I am using AC Power (average last 15 seconds), SOC & Battery Capacity to estimate remaining time (at current usage) until the battery hits the minimum SOC.

With 1% increments (@ 400W usage) and a 20 kWh battery, this gives 30 minutes. I would like to try and get better granularity than 30 minute jumps and I know that my BMS has this granularity (even if it is not precise, the relative aspect is still useful) and I believe that it sends it via CANBUS but it appears that the Victron nodes round it to an integer.


A better question would have been... has anyone written their own nodes to exploit this?

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xsilvergs avatar image
xsilvergs answered ·

I use the Modbus nodes to read data instead of the Victron nodes. I think one of my previous posts has some info on this.

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