Product Suggestion: option to ignore Stop Discharge signal from CANbus BMS

DIY
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1

I have an EasySolar 48/5000 and have upgraded from my 48V stack of AGM batteries by adding some 48V LFP batteries with embedded CANbus BMS. They have a Victron CANbus mode and work OK; their SoC is visible in every Victron UI except the BMV700 which only sees the AGM batteries.

The only problem comes when the weather is bad and the LFP batteries reach their lower discharge limit. At that point they BOTH

  1. toggle their discharge FET to stop themselves discharging AND
  2. send a signal via CANbus to stop the inverter inverting.

At this point, my AGM batteries are still nearly full and would happily power my AC demand for another day. But their SoC is ignored and the EasySolar/MultiPlus just shuts down AC output.

It’s useful for the EasySolar to get SoC from the LFP BMS, but very dysfunctional that it should respect the CANbus “stop discharge” signal in this way. The BMS is already protecting the LFPs by toggling their discharge FETs, so there’s really nothing the EasySolar has to do.

There may be other use cases, other BMS’, where respecting “stop discharge” would be useful. So my product suggestion is that within the Victron UI there should be a toggle to “Ignore BMS Stop Discharge signal”.

I got into this situation with dual battery types because

  1. I needed more storage, and
  2. my AGM batteries are ~3 years old and too good to throw away but extra AGM would apparently suddenly age to match the original set, which is throwing away a substantial fraction of the value on the first day.

It’s hard to imagine I am the only one in this situation.

Thanks for your consideration.
Graham

2

Sorry. I am probably missing something here. How exactly does that work? I mean. Your LifePo4 batteries are emptied long before your parallel coupled (I presume) AGM batteries? What Amp hours are we talking about?

And my two cent is. No. Please keep safety as is. A BMS can fail and then you seriously want to have additional protection.

3

I have nominally 200 Ah of AGM and 100 Ah of LFP in parallel. The LFP
discharge curve is very flat with a sharp turn at the ends of the range,
so the BMS says “stop discharging” at a voltage where the BMV 700
monitoring the AGM says “97% full”.

I don’t get your point about safety. If the BMS were to fail, then I
would not get a digital “stop discharging” signal from it, so the
setting I propose has precisely zero impact at that point.

I am using the LFP charging profile. Others in this situation seem to
say, don’t listen to the BMS and use the AGM charging profile. That also
seems to work.

Ngā mihi and Best regards,

Graham

4

Ignoring a bms fault signal is unlikely to ever happen. It is an external trigger for safety to protect the battery.
In your environment that config is completely unsupported and I wouldn’t see an appetite to modify the system for that use case.
You are better off disconnecting or setting the bms to ignore on the gx and managing the system via a shunt covering the full pack.