Batrium SoC stays same as voltage creeps down

[callmeburton]

Was originally thinking I wasn't going to need to post about this because the voltages were 3.4 when I first noticed this.

I have my batrium setup to do ramped charging dropping the requested amps starting at 85% SoC to 15, 90%/6a, 95%/2.4a, 97%/0.6a respectively. This was done with the idea of doing even less harm over time to the batteries while topping off.

What I have noticed is the Batrium will reach bypass voltage (3.5) on all cells and reset the SoC to 100% then then voltage will creep down overtime like there is a parasitic load on the battery which isn't accounted for while still showing ~100% SoC. What took the cake this morning was the voltage reading down as low as 3.31 and knowing the actual voltage is likely 3.28/9 at the cell while the Cap Empty (or remaining capacity) is sitting at 279.5 amps :/

Thoughts on what is going on here? Wire diagram here for this setup, everything using DC negative should be terminating north of the battery on the shunt https://diysolarforum.com/threads/i...bank-and-sma-si-load-center.52698/post-707395

 

[400bird]

It shows 19.5 watts in your screenshot. Is that constant? Are you sure the shunt direction is correct?

Where is you Batrium powered? Looks like you're running it from a 24v power supply. Where is that powered?

 

[callmeburton]

It shows 19.5 watts in your screenshot. Is that constant?

No this bounces around a little. The GRID is currently coming into the Sunny Island AC2 input so it will show anything from -27 to 40w on average when it is setup this way and the battery is beyond the 97% SoC mark. If I disconnect the grid then the loads going out will match the use for the circuits I have setup on the SI as critical loads.

Are you sure the shunt direction is correct?

The Shuntmon is connected with the voltage sense lead toward the inverter and the com cable toward the battery. Second picture here, while a little messy since I was testing stuff and hadn't tidied up wires yet, shows the shuntmon as installed. https://diysolarforum.com/threads/i...bank-and-sma-si-load-center.52698/post-673445 Looks like there is an unwired picture in the post above as well. The terminal bar left of the shunt is BS1 in the wire diagram where all DC loads connect to and with one wire going out to the inverter side of the shunt.

Where is you Batrium powered? Looks like you're running it from a 24v power supply. Where is that powered?

Positive from Bat+ connection to main DC breaker goes to the Meanwell DC/DC which powers the watchmon. The negative for the meanwell connects to BS1 in the diagram which is the inverter side of the shunt ... no negative wires extend from the battery side of the shunt. In my mind this means all DC loads should be read by the shunt.

It appears the SoC was set to 100% per the batrium protocol around 1pm EST 2 days ago

 

[400bird]

How long does it sit like this?

I was asking about shunt direction, meaning does discharge show negative watts and charge show positive? If not, you can swap the direction in the software.

Considering you're showing an average positive wattage, I wouldn't expect it to draw down the cells.

With lifepo4, it is normal for them to settle down to something closer to 3.4 volts. But, 3.3 is not what I'd expect.

Are you sure you're not pulling more energy from it? Like the inverter's idle draw all night?

 

[callmeburton]

How long does it sit like this?

Varies but since I have the grid hooked up to the inverter the batteries are not really in use right now. This morning low voltage is 3.32, high 3.34, requested charging amps .6, actual charging amps .7, SoC 280.000 indicated. If I were to disconnect loads and simply let it sit it would eventually get back up to 3.5v for all cells then reset the SoC and settle back down I presume to where it is now.

Considering you're showing an average positive wattage, I wouldn't expect it to draw down the cells.

The average in / out a day is actually pretty close. daily history for discharge is 1.122kWh and charge is 1.646kWh

With lifepo4, it is normal for them to settle down to something closer to 3.4 volts. But, 3.3 is not what I'd expect.

What I am thinking of doing now is disconnecting loads and having the inverter charge the batteries from grid. After the batrium resets SoC turn off the inverter and batrium for a day (not sure how long it would take) to see where the cells settle. Another thing I was thinking about was calibrating the cellmon as I know the voltages it reads are off from actual cell voltages by 0.02 if I recall but that likely isn't required for this experiment.

Are you sure you're not pulling more energy from it? Like the inverter's idle draw all night?

The system draws about 30w when the grid is not connected to the inverter and the loads are disconnected. Since the grid is connected all the time though that goes back into the battery pretty easily. The system hooked up to the grid uses 1.69A a day and charges 2.59A so it will slowly go up .9A / day over time where it will eventually hit bypass mode and reset the SoC.

I know voltage is not an indicator of SoC but on average the pack should be around 87% but that is an educated guess .. would need to take measurement at the pack terminals to know better.

 

[callmeburton]

Ironic my last update was a week ago. This morning the pack finally reset the SoC ... it claims only 3Ah went into the pack before this happens but at this point idk what to believe. And, since we are in peak brownout season I don't want to remove the loads from the SI to let the battery sit a day with everything turned off to see where it lands. Guess that means trusting the shunt readings for now.

 

[callmeburton]

UPDATE:
100% speculation at this point. My cutoff voltage is 3.5 set via the Batrium "longlife" settings for LiFePo4 batteries. If I have default settings the cutoff voltage is ~3.64. So my speculation is because my cutoff is 3.5 after it reaches 100% SoC (meaning all cells are at cutoff voltage) and stops the battery appears to 'creep down,' in this case it is back at 3.31v again, vs a higher voltage because of the voltage being lower.

I am tempted to set the Batrium to "typical" and have it charge to 3.64 to see if it then settles at 3.4 as I would expect it to if it was truly 100% SoC.

 

[callmeburton]

Update:
Day three I think with nearly stock settings ... The main difference being the ramped targets are not stock as I adjusted them to match the pack and my charging sources. 112 @ < 85, 15 @ < 90, 6 @ < 95, 2.4 @ < 98, 0.5 @ > 98 ... charging voltage was adjusted to default which is 59.2 (this allows for the 3.65 voltage bypass)

After three days, and two manual resets of SOC I am sitting at 3.31-3.33 ... meaning I could be shy 50+ amps right now :/
Current settings here https://diysolarforum.com/threads/final-lfp-charging-settings-with-batrium-bms.57938/post-739892

Going to cut off the grid power to the SMA SI and ride on the battery down to maybe 35% then let it charge back up from there to see what happens with the top balancing of the pack.

 

[callmeburton]

Update:
pack went through a recharge phase and was sitting out around 3.5 for a lot longer than I wanted. So drained the pack down again and set to "long life" settings again and let it charge back up.

It has been 3 days since the SoC was reset and the batter dropped down to the 3.1-3.33 voltage range. What is interesting is in those 3 days the pack has gone from 279Ah to 284.5Ah ... and it is still slowly growing. I don't think the batrium stores the daily high Ah favoring instead to show the SoC but it would be interesting to watch this to see how much gets in there before it does another charge cycle and resets the SoC.

Current max daily SoC is 102% Just going to let it ride out to see what happens ... I will be modifying my SoC limit controlling my remote disconnect breaker to a higher SoC so it won't trip by being something like 110% over time. Would be "fun" to have everything shutoff because the SoC creeped up too high.

EDIT:
Looking at the last 5 days of statistics I can see ~6ah going into the battery each day and the cell voltage is 3.2-3.33 ... I suspect this will continue till it gets closer to the real top. Some mechanism is resetting the SoC to 100% each morning but I am not sure which part of the logic is doing this.

 

[callmeburton]

UPDATE:
Got tired of waiting so I told the battery it was at 90% SoC till it got up to 98%, then noticing the battery voltage was still low I told it was 90% again. Over the last couple of days I dumped in ~80 Ah on top of the ~140 from when I let it charge from what I thought was 50% ... was likely closer to 25%

I am hoping this resets the SoC correctly. So the next test will be to drain the battery down and let it charge back up again to see where it lands in the voltage range vs SoC range.