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DIYBMS & Victron Integration - Couple of questions and one feature suggestion

Hi Everyone - My first post here.

Im a home powerwall builder here in NSW Australia. I have a 45kwh Nissan Leaf based powerwall in 14S21P configuration ~800ah.

I currently use Batrium BMS and am seriously considering making the switch to DIYBMS.

As I use Victron inverters and MPPT’s, I will need the new Victron integration and have a question or two and a feature suggestion regarding the Victron Integration (as requested by Stuart).

Q1. When doing a full DVCC Victron integration Do I require the DIYBMS Shunt, or can the DIYBMS grab the data from the Victron Shunt? Another way of asking is can either shunt be used?

Q2. What are the appropriate Victron DVCC Settings when using this BMS? (SVS on/off, etc)

Feature Request: I know Stuart was after feedback on the Victron integration and one thing the Batrium lacks is variable charge rate charging (based on say SOC or Battery Voltage.

When I have full sun, I can charge at 150+ amps - Which is fine when the cells are at 4v, but as we approach 4.1, the charge rate needs to be throttled back - to avoid some cells going to high.

The RECBMS has published their algorithm for this - And it would be ideal if the DIYBMS could do the same:

Battery Pack’s Charging Algorithm (from their instruction manual):

The communication between the REC BMS and the Victron CCGX is established through the CAN bus. All the parameters that control the charging/discharging behavior are calculated by the BMS and
transmitted to the CCGX unit in every measurement cycle.

The charging current is controlled by the Maximum charging current parameter. It’s calculated as
Charge Coefficient CHAC x Battery capacity CAPA. The parameter has an upper limit which is defined
as Maximum Charging current per device MAXC x number of inverter devices SISN.

When the highest cell reaches the Balance start voltage settings, charging current starts to ramp down to 1.1 A x Number of Devices until the last cell rises to the End of Charge Voltage. At that point the Maximum charging voltage allowed is set to Number of cells x (End of Charge Voltage per cell – 0.2 x end of charge hysteresis per cell). End of Charge SOC hysteresis and End of charge cell voltage hysteresis is set to prevent unwanted switching. SOC is calibrated to 100 % and Power LED lights ON 100 % Charge optocoupler is turned off. Charging is stopped in case of systems errors (See System Errors indication chapter). SOC is calibrated to 96 % when the maximum open circuit cell voltage rises above the 0.502 x (Balance start voltage + balance end voltage), minimum open circuit voltage above balance start voltage and system is in charge regime.

There is also a discharge algorithm, however, this is less important.

The manual is located here if anyone is interested: https://www.rec-bms.com/datasheet/UserManual_REC_Victron_BMS.pdf

Great work Stuart - I joined your Patreon a while back and am monitoring the progress. I have added the PCBs to the cart in JLPCB a few times, but I’m worried that I will be unable to source parts… I will need to bite the bullet at some point and just place the order.

Thanks Again!

DIYBMS requires its own shunt, although you are likely to still need the Victron shunt for monitoring on the Victron side. DIYBMS shunt data is transmitted to the Cerbo GX device.

I don’t run a Victron setup, so unfortunately I can’t specify what these should be.

Looking at the details you list from REC BMS, that looks interesting.

At the moment, DIYBMS has simple DVCC settings largely driven when a module enters bypass, but this could be changed to something based on SOC or voltage etc.

What I’m looking for is somebody to define what is likely to work for them in a suitable Victron environment/setup - I don’t have that equipment so have no easy way to test the setup.

Hi Stuart

Thanks for the reply.

I am finding there is a disconnect between BMS makers (for example, Batrium and your own solution) and the hardware they integrate with. The end result is potentially poor integration with virtually no documentation - and no one person is certain how it all actually works.

I realise it must be hard however as there are so many systems that are potential integration possibilities. Victron thou have an awesome little system and are very popular, so would make a great choice for tight well tested integration.

In my experience with the Batrium unit, its shunt data gets sent to the Victron GX device - and for all intents and purposes, it appears as though there is a Victron shunt in the system.

My guess is the DIYBMS shunt works the same - So no Victron shunt would be required.

The DVCC integration is extremely important with a Victron system. When enabled all charge parameters are controlled by the battery (BMS) rather than the charge settings in the inverters / MPPT units.

I would love to see similar integration to the RECBMS unit - if that helps.

Does the recbms have a published interface?