Parallel Lithium battery banks going into Hibernation mode.

I have 2 48v Lithium Battery rack mounted banks connect to Deye 5kw Hybrid inverter in Lithium Mode.
The BMS is correctly communicating with the Inverter.
My problem is, late in the afternoon the Slave battery is taking the load and the Master is in Idle Mode.
In the morning the Master has gone into Hibernation Mode because is has not been discharging.
I then have to do a reset to get it back to charging Mode.
It doesn't do it all the time but it does it most days.
I thought both batteries would take the load and discharge equally.
Any ideas why this would be happening.
The manufacturer (HRESYS) says to do a restart but I am getting tired of doing this nearly every day.
Could it be a BMS failure.

Thanks.

Deyedreamer said:

I have 2 48v Lithium Battery rack mounted banks connect to Deye 5kw Hybrid inverter in Lithium Mode.
The BMS is correctly communicating with the Inverter.
My problem is, late in the afternoon the Slave battery is taking the load and the Master is in Idle Mode.
In the morning the Master has gone into Hibernation Mode because is has not been discharging.
I then have to do a reset to get it back to charging Mode.
It doesn't do it all the time but it does it most days.
I thought both batteries would take the load and discharge equally.
Any ideas why this would be happening.
The manufacturer (HRESYS) says to do a restart but I am getting tired of doing this nearly every day.
Could it be a BMS failure.

Thanks.

Click to expand...

you could try the "activate battery" setting.... but normally that is used to bump a very low battery

seems odd that battery would go into hybernation as power is ( or should be ) flowing through them...

how is your inverter connected to your batteries and the batteries to eachother ?

The Inverter is connected to a common busbar and each battery is connected in parallel to the busbar.
See image below.
Batteries are connected in parallel with comms cable and Inverter is connected with CAN cable.
Batteries are set up as Master and Slave.
The Master is going into Hibernation Mode.

Battery cables need to be EXACTLY the same length.
Btw. why the busbars? Why not connect the batteries in pure parallel with red going onto the first and black going out from the last one.

Not sure I understand your response. Do you mean removing the busbars.
Can you draw a diagram if possible.
The busbars were used to connect multiple batteries.
I will address the cable length issue.

LydMekk said:

Battery cables need to be EXACTLY the same length.
Btw. why the busbars? Why not connect the batteries in pure parallel with red going onto the first and black going out from the last one.

Click to expand...

Some actually recommend going with busbars for parallel.
In any case, the busbars probably aren't the problem, unless there is a loose connection.

For the OP: Have you charged each battery fully before putting them in parallel?

Yes they have been fully charged as they have been in operation for around 8 months.
I am going to even up the battery cables.
Although the positive and negative cables are of different lengths due to batteries being mounted vertical on wall.
I will adjust all positive and all negatives to be the same length if that makes sense and see if it makes any difference.
I will double check all the connections.
Thanks for your advice.

Just one thing I had a problem with myself: make sure there are no washers between the busbars and the ringlugs on the cables. Direct contact.
Washers, locknuts and nuts on top.

Thanks, I will check things over.
I have just adjusted a negative battery cable length and everything is fine so far.

I have adjusted the battery cable length.
After 1 day the Master battery is still going into hibernation mode.
I am waiting on a response from the dealer.
Do the batteries need to be fully charged and the same voltage before switching on.

Nothing wrong with busbar cabling as I see it unless there is a bad connection?. What are those dc breakers? Are they in the batts or separate breakers wired in path? I think we need to clarify what 'idle' is and why. If one is charging or discharging the other should too unless it is in an OVP or UVP state or following some setting defined in BMS.. or like you said faulty.

Any displays on the batts to check voltages? Software? If so what's the voltage reading of them in the morning after reset? Alarms?

From your description kinda sounds like master node is not at the same overall SOC and is hitting bottom (eg. a cell drops under voltage, maybe a really low cell keeps dragging the pack down?).. you reset it in the morning to clear the UVP and it starts to charge, takes some in but never gets enough to match the slave, discharges to UVP state.. goes 'idle' and then counts down overnight to some predefined timer setting that shuts it down. You reset in the morning rinse and repeat.

One would think they'd settle over time but maybe instead they're getting farther out.

I've made a lot of assumptions but more details can help. Voltages, cycles times, loads and how much charge they get etc.

Thanks for your reply.
I will get back with some more information.

The DC breakers are in-line on both positives.
No loose connections anywhere.
Battery Voltages in Morning:
Load over night: 80 watts (50 watts inverter, 30 watts consumption load).


Additional info: I noticed on the Solarman app, batteries are at different SOC 89% and 85% throughout the night. (4 percent difference).
See the dip on the orange SOC line below. Not sure why they would be different when they have been charged all day since 9am.

Deyedreamer said:

Do the batteries need to be fully charged and the same voltage before switching on.

Click to expand...

Yes! That's what I recommend previously.
Don't count just on voltage, fully charge each one separately before paralleling.

Thanks for your advise I will give it a try.
I have been advised by the dealer the overnight discharge of 100 watts was causing 1 battery to go into hibernation which makes sense.
I have connected additional cycling load to run overnight and it seems fine so far.
I will continue to monitor progress.
Thanks for all who commented.

Everything appears to be working as it should after increasing the overnight load.

Did they tell you why? I would think even if the one battery does not see a load (that on its own is curious b/c 2A is still enought to be shared on 2 parallel batts if they are around the same soc) over night it shouldn't power down that quickly. What's the setting on the batteries/bms?

I will check and get back with results.