question

paulcooper avatar image
paulcooper asked

BMS connection lost four times in two months

I realise this question has been asked a few times in this community but they all occurred some time ago and in one response @Guy Stewart (Victron Community Manager) said that it has been resolved in a firmware update. I have the latest firmware:

  • BYD Premium LV battery
  • BMU firmware v1.22
  • MPPT RS 450/100 (firmware v1.10)
  • Multiplus II GX 48/5000 (firmware 498)
  • GX firmware v2.92 Large

Each time the MPPT was displaying #67 BMS connection lost and the MPPT disappeared off the Remote Console pictogram. A reboot of the Multi fixes the issue. The first time the error occurred was in October 2022, then once a few weeks ago, and today I got the error twice. After the second occurrence I reseated the VE.Direct cable in the Multi and the MPPT and will see if that improves matters.

One thing to note is that the error seems to occur when the Multi is changing state – the first time was back in October when the battery reached 100%. Today the error occurred when the Multi was switching ESS state from:

  • "Optimized + BatteryLife: SoC below dynamic SoC limit", to
  • "Optimized + BatteryLife: self consumption"

This can't be just a coincidence, surely?

Multiplus-IIBMSerrormppt rs
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paulcooper avatar image paulcooper commented ·

It happened again this morning, just as the Multi was switching from "Optimized + BatteryLife: SoC below dynamic SoC limit" to "Optimized + BatteryLife: self consumption".

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3 Answers
anthony avatar image
anthony answered ·

Hi, There is a later version of FW available for the MPII - V500

Also have you checked the BMU CAN cable?

Anthony

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paulcooper avatar image paulcooper commented ·
Many thanks - I'll update the FW. I have checked the BMU CAN cable but I will do it again. The reasons I don't think it is hardware are the following:

1) My MPPT disappears from the Remote Console at the moment this happens. So it seems to me that the MPII and MPPT stop communicating.

2) It always happens at a state change in the MPII. For example, this morning the error happened again at exactly the time that the MPII changed from Below Dynamic SoC Limit to Self Consumption. Also the VE.Bus state momentarily changed from External Control (where it should remain) to Bulk.

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nickdb answered ·

The multis cannot cause or affect BMS lost errors.

These are either a bad cable or, the BMS itself is shutting off and blocking discharge which would result in low voltage alarms on the inverter.

BYD should have a bms utility that allows you to look for bms alarm/error states. I would check that.

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paulcooper avatar image paulcooper commented ·
Thanks @nickdb . I think the MPPT reporting BMS lost is a symptom of another problem, that is the MPII and the MPPT stop communicating. Please see my comment to @Anthony above for further details. But I will check the BMS log to see if there are any further clues.
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nickdb avatar image nickdb ♦♦ paulcooper commented ·
Losing comms isn't an issue of itself, this happens every time you restart or update a GX.

They revert to internal limits, so you need to check that the manual settings on the mppt and the inverter are set correctly for your battery, if these haven't been set right you can end up with a problem which the BMS reacts to.

How is the mppt connected? Best check cabling etc and get that link stable.


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paulcooper avatar image paulcooper nickdb ♦♦ commented ·

I'll check the settings.

My MPII is connected to the BYD BMU via BMS-CAN. My MPPT is connected to the MPII via VE.Direct.

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paulcooper answered ·

Thanks @nickdb and @Anthony. This issue has developed and I have expanded on it in another posting. Please see: https://community.victronenergy.com/questions/175242/multiplus-ii-gx-regularly-rebooting-and-causing-mp.html

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