How should LFP battery CANbus status be connected-up?

Q&A and troubleshooting
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1

I have a Fogstar LFP battery (Seplos BMS) connected to my Victron system (MPII runing ESS assistant, MPPT, GX). It provides CANbus status data, and can impersonate a range of protocols, including ‘Victron CAN’ and ‘Pylontech’. I currently have it set to ‘Victron CAN’.

I can’t work out how to connect this info to my GX system such that it is used by the ESS to monitor charge state. I presume this info will be way more accurate than just watching the voltage, which is what I think it is doing at the moment.

I watched the training on BMS and LFP but whilst it was informative it provided no clue on how to connect up a battery that reports its status over CANbus. I assumed this would be simple/obvious, but I’m failing to find the right document. Or maybe it’s not simple/obvious?

Also I bought a VE.direct MPPT controller. (250/70). If I had bought a VE.Can version of that, could I have plugged the battery CAN output into that to let it grok the battery status? The MPII needs this info as well, so maybe that wouldn’t help much.

I must admit that I have not understood the architecture of the control-systems here yet. I do understand that in ESS mode the MPPT is sent a message to say ‘don’t think for yourself - get your charge rates from the system (using DVCC)’. But who sends that message, and the changing rates? Is it the MPII ESS assistant that sends that info, or the GX? I guess it’s the MPII sending it via the GX (where the MPPT VE.direct is connected). But maybe the MPII can’t do that and a GX is required?

And how does this change when DESS is enabled?

So many questions…

My system seems to be doing a reasonable job of estimating and reporting battery SOC already, despite the CAN bus not being connected up, but I have no idea how it is doing it? I guess it knows the battery capacity and is keeping track of the energy flow in and out via the MPII and MPPT?

So, should it use the CANbus data? If so, how do I connect it up to do that?

I feel like I have missed a document somewhere…

2

Your battery has to be connect on the can bus connection for the battery at the GX device

Your battery will force dvcc if set on pylontech, the bms will control charge/discharge rates and communicates that with the GX if set up right

The GX controls the whole system, tells the mppt and multiplus what to do with data from all connected devices

You should read some manuals, everything is explained there

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

https://www.victronenergy.com/live/battery_compatibility:start

3

Hi

The CAN of the Seplos is a 250kbps.

The CAN of the smart solar is a 500kbps one

As a matter of fact, having both running means having two separated CaN buses, as not on the same speed, unfortunatelyw

For my setup, I only have one CAN bus, on which I connected my BMS Seplos v3. My smart solar 250/70 Ve.CAN is connected with a VE.direct cable.

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4

OK. I have it all working.
The Seplos BMS in the Fogstar ‘v4’ (not sure if it’s actually different from the ‘v3’ BMS) uses 500kbit/s for CAN comms.
Plug canable interface it in to RPiGX and can0 appears automatically under ‘services’.
Set the BMS to use ‘Victron CAN’, and select ‘CAN-bus BMS LV (500kbit/s)’ under can0 in the Victron GUI and then a ‘BMS16S200A-SP112’ appears under the ‘devices’ list. You can give it a nicer name under there.
Easy peasy in fact.

BTW when there is no CAN or serial status from the battery, how is the ESS system estimating battery SOC? It was 20% wrong by the time the batt got down to 45% (UI said 25%).

5

I’ve now enabled DVCC with this BMS. I see this battery is not on the ‘Battery Compatibility’ list yet. Would it be useful to provide some more detailed feedback, or do some tests on how this BMS behaves? I see offgridgarage Andy has tested the earlier v2 (10E) version.

Happy to help if that’s useful. Is there anyone else using the Fogstar v4 with a victron setup?

6

Very few batteries are in the battery compatibility list, and I do not expect this to change much - it solely means that officially, Victron will not help you in configuring it in case you are facing issues… bit definitely does not mean it does not work properly… as you have seen it does, after the proper setup.

Fogstar v4 is another Seplos kit, with a Seplos v3 BMS - and only this latest really matters when we talk about interconnection with the inverter :slight_smile:

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7

Answering my own question for anyone else reading this.

Also I bought a VE.direct MPPT controller. (250/70). If I had bought a VE.Can version of that, could I have plugged the battery CAN output into that to let it grok the battery status?

The answer to this is ‘no’. Or at least the MPPT VE.Can devices cannot be used with DVCC - you need a VE.direct MPPT for that.

8

All MPPTs can or otherwise are controlled by DVCC.
The issue you are probably having is the two different can bus speeds. Mppts are 250 and bms is 500.
Which means they can not share a can bus. You need a GX that has two and can be set to two different speeds.

9

I disagree. This can work with MPPT and BMS on separate CAN buses as alluded to by @msevestre