BMS communication issues

[cojmh]

Thanks for your message

Yes - I think the cable is correct now.

I have dropped the charge voltage on the Solax to 53.2V as you have suggested and it appears to have kept the setting too (Will double check again tomorrow)

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.

I did try using a different battery as a master to eliminate any potential faults with one particular battery pack - it made no difference so I was pretty sure it was a problem with the inverter.

[cojmh]

I sincerely hope it has been a CT clamp and wrongly wired bms lead. Fingers x'd.

I have changed the CT clamp and I have now watched the batteries both charge and discharge seemingly when the load/PV generation changes - at the same time the smart meter seems to say 0 or very little grid usage (<100W) whilst it is doing this.

This is a massive improvement from either the batteries charging a full rate from the grid or discharging at maximum rate back to the grid.

So I am going to tentatively say that I think it is working as it should - I will have to monitor over a few days I think just to make sure it is doing what I think it should be with the limited info I can get out of the solax unit.

Interestingly the Solax unit is still saying "BMS Disconnected" - but the behaviour of the system seems to be what I would expect it to be irrespective of this. So I think that this is a real red herring (and what I was initially using to try and figure out if things were correct).

I will just have to see what happens over time and hopefully adding my 4th battery (which arrives next week) will not cause me any more upsets!

[cojmh]

Want to say a huge thank you to everyone who has helped me with this. It is really appreciated!

If this has worked then I will be moving on to my next two projects (Solar water heating) and putting excess energy from the PV (above what the batteries can store) into water heating!

So watch this space!

[Joeboy]

Want to say a huge thank you to everyone who has helped me with this. It is really appreciated!

If this has worked then I will be moving on to my next two projects (Solar water heating) and putting excess energy from the PV (above what the batteries can store) into water heating!

So watch this space!

[Tinbum]

I would be careful if it is still saying BMS disconnected.

To give an indication to check to see if the BMS is instructing the inverter - see if the battery current steps down as the SOC increases. It normally starts around the 90% SOC, and will suddenly drop to 14A (on mine), then to 7A (on mine). The battery will also not start charging again unless it has dropped to 95% SOC

[cojmh]

I would be careful if it is still saying BMS disconnected.

To give an indication to check to see if the BMS is instructing the inverter - see if the battery current steps down as the SOC increases. It normally starts around the 90% SOC, and will suddenly drop to 14A (on mine), then to 7A (on mine). The battery will also not start charging again unless it has dropped to 95% SOC

OK, I will keep an eye on this.

Just to check I understand what you are saying - basically as the battery starts to get full, the charging current should drop off?

The only way I have of telling the state of charge is the LEDs on the front of the Pylontech batteries. The Inverter does have a % for the battery capacity but I am suspicious of the figures it gives.

I will keep an eye on it and feed back on here in case it is useful for anyone else in the future.

[nowty]

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.

[Tinbum]

Just to check I understand what you are saying - basically as the battery starts to get full, the charging current should drop off?

Yes, but it is doing it in STEPS that is important. You should see it suddenly drop which will show the BMS is communicating with the inverter. I suspect it won't be.

(The current will drop off slowly as the battery resistance increases if the BMS is not connected).

[nowty]

Just to check I understand what you are saying - basically as the battery starts to get full, the charging current should drop off?

Yes, but it is doing it in STEPS that is important. You should see it suddenly drop which will show the BMS is communicating with the inverter. I suspect it won't be.

(The current will drop off slowly as the battery resistance increases if the BMS is not connected).

The Pylontechs look after themselves and manage the current in / out as necessary. I've been running a stack of them on my sunny island without BMS for years.

[Tinbum]

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.