Victron Venus GX and Electrodacus SBMS0

[Frank Thompson]

I am researching BMSs to use with the 8 280an EVE Li cells I have on the way and my existing Victron multiplus 3000,  mppt SCC, BMV702 battery monitor, and Venus GX controller.  In my current system the Venus GX receives state of charge info from the BMV702 and can regulate the inverter charger and mppt scc.  But, with my new batteries can I use and Electrodacus and connect it to the Venus GX so that the Venus GX will regulate the chargers based on info from the Electrodacus?  I know there are ways to use the auxiliary inputs on the multiplus so the Electrodcaus can regulate it directly, but the only communication port on the mppt scc is already used to connect it to the Venus GX, so I was hoping the Electrodacus could provide the needed informaiton to the Venus GX and it would still control charging and inverting by the multiplus and mppt scc??

[Dacian Todea]

The SBMS0 will stop the charge or discharge when battery is fully charged and also the SBMS0 will calculate the battery SOC more accurately than the BMV702 that will be redundant.

The larger Victron MPPT's have build in remote ON/OFF connector is usually a two pin connector with a wire link. If it is one of the smaller current MPPT's then you will need this remote ON/OFF cable to connect to SBMS0 and in that case the Venus GX can no longer be used  https://www.victronenergy.com/accessories/ve-direct-non-inverting-remote-on-off-cable

Also I do not think there is anything that Venus GX offers that is not also present in the SBMS0.

[Frank Thompson]

Thanks you confirmed by fear that the mppt scc can't work with both the Venus GX and the SBMSO so I will have to think this through some more.  This is from the Venus GX manual:  "In systems with an Managed CAN-bus BMS battery connected, the GX receives a Charge Voltage Limit (CVL), Charge Current Limit (CCL), Discharge Current Limit (DCL) from that battery and relays that to the connected inverter/chargers and solar chargers.""  I was hoping the SBMSO would work with the Venus GX in way that the Venus GX could then to all the management of charging and inverting.   The Venus GX provides a nice graphic system overview and ability to look at performance of each device on my phone or laptop.  My understanding is it also manages charging by the multiplus and mppt scc so they work together appropriately?  

[Frank Thompson]

So I'm starting to see a lot of advantages to the SBMSO even if I'm not keen on getting rid of the Venus GX, but have a few more questions.  So it looks like I can use a shunt for my battery and multiplus and another for mppt scc to totally monitor my system.  My maximum power usage would be 200a and I have 6 100w solar panels, can you suggest what shunts I should use?  Second without the distributed voltage and current control function of the Venus GX, how would this system sort out charging between the multiplus and mppt scc?  Lastly, I currently have my multiplus and mppt scc set up to not charge below 32 F, does this bms have a function to prevent low temperature charging? 

[Dacian Todea]

Yes there will be a battery shunt and a charger shunt so you can see the solar current the battery current and SBMS0 can then also calculate the Load current.

The 600W of PV panels will likely result in a max of around 20A in a 24V LiFePO4 so not much. 

Say you get 20A from PV panels and you have a 50A load on the inverter. 

Then the PV shunt will measure 20A and the battery shunt will measure 30A going out of the battery thus the SBMS0 knows battery discharges at a 30A rate it knows PV provides 20A and calculates the Load as 20A+30A = 50A thus everything is known.

As another example say you still get 20A from PV panels but Load is just 7A then PV shunt will see 20A the battery shunt will see 13A of charge current and from this two it will calculate the Load as 20A - 13A = 7A

Not sure where this system is installed and why you will want to charge from grid but that is not a problem.

You can set the SBMS0 to stop both charge and discharge if battery temperature is below 0C (32F) but that will not be useful. If your battery is not inside a temperature controlled space then the only proper option is to have the battery in an insulated battery box that then has a heater with a separate thermostat set to keep battery above 10C (50F) at all times and that can be done with just a 10 to 15W heating element assuming you have a properly insulated box.

This way you can use your battery no matter the ambient conditions else if battery is not heated and insulated and ambient is below freezing you may not be able to use you battery for days or even months.

[Clowny666]

I sort of understand your feelings, the Venus GX does give you a nice screen to look at and use compared to the SBMS. But the SBMS control is far superior to the Venus charging, for example the bulk, absorption, float on the Victron equipment is completely wrong for LiFEPO4 batteries in my mind. So, there isn't one easy solution to get the data from the multiplus/chargers into the SBMS whilst using the Venus OS (when on shore power for example). So, you could get into the realms as I am, of writing a SBMS driver to get the data into the Venux GX and working it around that way (there are working versions from Chargery that will be easily adapted, or there is a guy that has done an SBMS version but refuses to share), or there is a raspberry PI docker image that spoofs data onto the DB-Bus which you could adapt to read the SBMS MQTT output and translate into the Venus OS.

[Dacian Todea]

You mean large screen by nice screen or the graphic ?

I think SBMS0 offers many view options including one that looks similar to Venus GX

[Frank Thompson]

OK so I think I understand now I'm not losing anything by giving up the Venus GX for the SBMS0, and in fact I'm gaining cell level monitoring that will control my charging and discharging. So the remaining tradeoff I'm evaluating is a little bit higher cost going this route with the SBMS0, shunts, battery protect, and cable and configuring my 12v battery 2p4s; versus going 4s2p with two JBD 4s 150a bms's and my exiting Victron equipment.  Any thoughts on plusses and minuses of these two options?

[Dacian Todea]

There is no difference between 2p4s or 4s2p tho the later format is the preferred and used one.

Tho I think I know what you mean and it is not allowed to parallel two Lithium batteries only lithium cells can be paralleled.

So a 4s2p means groups of 2 cells in parallel and then 4 of those groups in series and you can write this as 2p4s but it is not common and can create confusion.

[Frank Thompson]

So my understanding is 4s2p and 2p4s are very different configurations at least the way people on the DIY Solar Forum use the terms.   I believe you are suggesting paralleling 2 cells and putting 4 of the pairs in series to create a 2p4s 12 v 560 ah battery and using the SBMS0 as a 4s BMS.  I understand the opinion that it may be better to parallel cells than batteries, and think I agree.  However 4s2p is regularly used to refer to 2 4s batteries in parallel , each with their own bms, and it seems many people do this.  There also seems to be no strong consensus on the DIY solar forum about which approach is better for a modest mobile system.  Hence my questions about which option to pursue.   

[Dacian Todea]

There is just a single correct configuration so if you say 4s2p or 2p4s it can only mean the same thing as what some in DIY community are doing is just wrong.  You will not see two parallel batteries in any commercial application.

All laptops with a 4s2p battery will have groups of two parallel cells then 4 of those groups connected in series. Same for any EV on the marked (not DIY) they will all have groups of cells in parallel then those groups connected in series.

Parallel cells are in absolutely no way different from a single higher capacity cell.   Parallel batteries are just not allowed that dose not mean people do not do stupid stuff.

If paralleling lithium batteries was an option then you will see EV's on the market with say 50kWh and 100kWh options by just adding another 50kWh battery in parallel but that is not the case and they will either add more series connected modules for higher voltage or they will have packs that have more parallel cells or higher capacity cells for the larger capacity packs.

There is the power wall that can be paralleled but you are not actually paralleling the batteries but you are paralleling the inverter outputs.   You can do the same thing have two completely separate systems with separate battery and separate inverter and then if the inverters have option to be paralleled on the output then that can be done. 

[Eric Nelson]

Seems to be more than one way to skin a cat. I am trying to use a mix of SBMS MQTT over wifi, VenusOS_Large on a Rpi3 with a MK3USB connection to a Multiplus and wrap it all in node-red.Still a lot to learn though. I like the data I am getting off the Venus/MK3USB side, gives me a bit more than the default Venus window. This is just a shed build for work from home and mostly I use the system like a UPS while most of my loads run off the mains AC. I have the multiplus configured to keep the battery topped up as I do have DC loads, when I am not getting enough from PV. The SBMS doesn't separate the charge current coming off the Multi, as it just goes through the first shunt with the load when engaged. With the VenusOS/MK3USB i can get the charge current it is sending, So I should be able to combine these data in a meaningful way. I'll keep trawling this and other forums for tips and clues.

Good stuff!

[Chris R8]

@Eric Nelson:did you actually do this with the mix off Electrodacus and Venus OS on a Raspi? Wanna do the same so I get all the info from the Victron gear.

I can also place the monitor of the Pi differently then the Electrodacus which needs to be near the battery, my main reason doing it.