BMS communication issues

[nowty]

Interesting- so the battery BMS will step down the current internally. I've not tried it as I don't want to risk loosing the battery warranty.

Yes I think they use solid state relays or similar to manage the current flow in and out if overloaded or overvoltage. I have monitored mine extensively measuring voltage and current in many different scenarios. I use them in parallel with two other battery banks of different lithium chemistry so I needed to know how they behaved.

When they are full they seem to go into standby whilst my other two battery banks are doing the work, then as the voltage drops, they wake up and start contributing.

I think the model of inverter cojmh has is quite an old model so its maybe not surprising it does not communicate with it.

[Joeboy]

Interesting- so the battery BMS will step down the current internally. I've not tried it as I don't want to risk loosing the battery warranty.

Yes I think they use solid state relays or similar to manage the current flow in and out if overloaded or overvoltage. I have monitored mine extensively measuring voltage and current in many different scenarios. I use them in parallel with two other battery banks of different lithium chemistry so I needed to know how they behaved.

When they are full they seem to go into standby whilst my other two battery banks are doing the work, then as the voltage drops, they wake up and start contributing.

I think the model of inverter cojmh has is quite an old model so its maybe not surprising it does not communicate with it.

Agreed, seen my batteries shutdown on their own too with no inverter bms input. It makes sense as it covers more scenarios so can further sales. OP, asTinbum said, best to keep an eye on your top and bottom voltages. From blasted mind something like 52.3v down to 44.5v if you run down to 10% soc but don't rely on those figures. I do rely on my bms!

[Tinbum]

With the BMS connected my Pylon (if just using a single battery) will charge at about 37A. When it reaches about 90% the current will drop from 37A down to 14A in a single step. It will stay at that until about 95% and will then drop from 14A to 7A. It will stay at 7A for a while and will then drop to 3.5A. After that it will taper down as the battery resistance rises. (Figures are approx., just from memory from a few months ago, when I was doing my CAN bridge).

Is that how they behave when no inverter communication is connected? Or is it just a gradual tapering down of current due to battery resistance?

[nowty]

With the BMS connected my Pylon (if just using a single battery) will charge at about 37A. When it reaches about 90% the current will drop from 37A down to 14A in a single step. It will stay at that until about 95% and will then drop from 14A to 7A. It will stay at 7A for a while and will then drop to 3.5A. After that it will taper down as the battery resistance rises. (Figures are approx., just from memory from a few months ago, when I was doing my CAN bridge).

Is that how they behave when no inverter communication is connected? Or is it just a gradual tapering down of current due to battery resistance?

To be honest I've never drawn a graph but last night when the charge voltage was at about 53V only about 1A was going into the Pylontech bank and 33A was going into each of the other battery banks. One by one the pylontechs go into standby and their LED lights go off.

When I used to use the pylontechs with my Sofar ME3000SP I think the charge current just tapered off, I don't recall any actual step change.

[cojmh]

Interesting- so the battery BMS will step down the current internally. I've not tried it as I don't want to risk loosing the battery warranty.

Yes I think they use solid state relays or similar to manage the current flow in and out if overloaded or overvoltage. I have monitored mine extensively measuring voltage and current in many different scenarios. I use them in parallel with two other battery banks of different lithium chemistry so I needed to know how they behaved.

When they are full they seem to go into standby whilst my other two battery banks are doing the work, then as the voltage drops, they wake up and start contributing.

I think the model of inverter cojmh has is quite an old model so its maybe not surprising it does not communicate with it.

Agreed, seen my batteries shutdown on their own too with no inverter bms input. It makes sense as it covers more scenarios so can further sales. OP, asTinbum said, best to keep an eye on your top and bottom voltages. From blasted mind something like 52.3v down to 44.5v if you run down to 10% soc but don't rely on those figures. I do rely on my bms!

From the earlier post I have limited mine to 53.2V and the bottom is 47V - Is this OK?

I am not relying much on the SOC on the inverter which seems to be much lower than what the batteries report on their LEDs

With respect to the charging - I have seen the batteries taper off the charging current when they are full.

Currently the smart meter is still saying 0W from the grid and the house is still powered so it seems to be working as I hoped. I will have to see what happens tomorrow when we have sun again.

[cojmh]

I tried to increase the charge and discharge currents up to 100A but the inverter keeps reverting these back to 50A - I guess I will have to live with that.

Your inverter has a max charge and discharge spec from the batteries of 50A I'm afraid, I just checked the datasheet. Your Pylontechs are rated to 37A each, so 111A in total but your limited by your inverter.

Yes, you are right .... they have so many different units listed in the same document I got it mixed up.

Fortunately it should be enough for most of my usage at 2.5KW maximum even though the inverter is actually capable of 5KW from the PV

[cojmh]

Just thought I would post an update one week on.

Not been a great week for Solar here (apart from today)

The batteries have performed well in my opinion - even though it still reports BMS disconnected.

The batteries charge and discharge as I would expect them to and everything seems to be stable and I have noticed the benefits already on the smart meter.

So, now I have to figure out a way to try and up my charging capacity, but I will start a new thread for that.

[nowty]

So, now I have to figure out a way to try and up my charging capacity, but I will start a new thread for that.

Any room anywhere for some extra PV and connect to a charge controller and tee it into the DC side of the battery stack (like Joeboy).

Or like me if you can get hold of a cheap second hand Sofar ME3000SP you can connect it up without any CT clamps and use the test mode to force charge your batteries, again tee'ing it into the DC side. That would give another 60A to take you roughly to the max rate of the battery stack and the 25mm DC cables. Legality is a bit dubious because the DNO would say its another bi-directional inverter even though I am only using it as a battery charger.

[Tinbum]

To be honest I've never drawn a graph but last night when the charge voltage was at about 53V only about 1A was going into the Pylontech bank and 33A was going into each of the other battery banks. One by one the pylontechs go into standby and their LED lights go off.

When I used to use the pylontechs with my Sofar ME3000SP I think the charge current just tapered off, I don't recall any actual step change.

I have some US3000C connected to some ME3000SP and they definitely step change. I'd just be worried that if the batteries became faulty then they wouldn't repair replace them under warranty.