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Strange - Gradual reduction of max SOC over time???

Jazzmonger

Jazzmonger

Hacker at heart
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Apr 29, 2022
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Location
Wilder, Idaho
I have a very strange thing going on w/ my 4x100ah LifePO4 battery packs. Before about 22 days ago, the highest SOC I could achieve was always 100%. Every day. Now the highest SOC I get is 85% and slowly reducing about 1% each day. this happens regardless of using PV charge or Utility. The dip on 8/31 was me doing a capacity test, and during that test I got a full 100ah into and out of the individual batteries.
1663775087172.png

My charge params haven't changed and the cell voltages reported at 85% SOC are all right around 3.425v, which should be 100%, so I'm inclined to think this is a BMS reporting issue/bug.

The battery vendor will be attempting a firmware update this coming Friday morning to try and fix the incorrect capacity numbers all the batteries are reporting, and who knows, it may also fix this. But I find it very strange regardless.
 
I see flat tops to the right, which tells me SCC has decided to limit voltage, stop putting current in. Double check voltage with DMM.

Do another capacity test. Maybe the reported SoC is slipping, just doesn't get reset to 100% because it is looking for a higher voltage to trigger reset.
 
Last edited:
Very odd... what SCC and what BMS?
Yes I'd definitely try another capacity test, but that amount of capacity degradation over a month is highly unusual
 
Hedges said:
Do another capacity test.
Click to expand...

What I actually meant was not "capacity test" (charge to full then discharge), rather just discharge, see how many Ah you can draw from it. To see if it is full when SCC stops charging, and you have plenty of charge in the battery and still have same capacity as before. i.e. capacity is simply under-reported.
 
Hedges said:
What I actually meant was not "capacity test" (charge to full then discharge), rather just discharge, see how many Ah you can draw from it. To see if it is full when SCC stops charging, and you have plenty of charge in the battery and still have same capacity as before. i.e. capacity is simply under-reported.
Click to expand...
I'm planning on doing exactly that tomorrow.

2 LV6548s in parallel, and the sw that works on the BMS is Pbmstools.exe. I think the manufacturer is Pace.
Module number is P16S100A.

1663823325002.png
 
Ok, it's like watching paint dry, but I think we've all done it. The capacity test revealed a full 382ah was taken out of the battery pack over 8 hrs. 2 of the 4 packs shut down when the lowest cell voltage in each pack reached 2.5v and that's when I stopped the test. SOC was 0% for about 1:10 but I was still pulling ~8A out of each battery, and It appears SOC on all batteries reset and is now climbing after I reapplied grid power.

BMS gets upgraded firmware tomorrow.
 
Sounds like you have full capacity still. But SoC drifts a bit.
I've got a JK bms and a chargery. Each have their own shunts to measure current and calculate SoC, and each do drift from each other a bit if the battery doesn't charge to real 100%.
My chargery shunt thinks 0.5amps is charging the battery even when there is no flow. So over time it will get inaccurate if not charged to 100% where it resets.
The bms should never stop charge depending on its state of charge calculation. It should be voltage based
 
Yup, all true. But when you have a controller like Solar Assistant trying to do power management based on an accurate SOC (not voltage) its important that it's right... otherwise it's useless.

1663917795836.png
 
Gee that's odd, I'd never run a system with charging based on calculated or measured SoC. That's just asking for trouble.
If you have the option to make it stop charging based on voltage, I'd change to that.
 
Try charging with 57v float and see if the SOC jumps up to 100%.
After that go back to 54.5 or 55V and see if it maintain 100% after a charge.
Everything in your system looks perfect so it probably needs a little calibration session.
 
Jazzmonger said:
BMS gets upgraded firmware tomorrow.
Click to expand...

Not necessarily a firmware issue, just a setting of what voltage forces it to reset SoC to 100%.

Or as Robby says, test by changing SCC settings for a higher voltage, see if that triggers BMS.
But I would suggest "Boost" voltage higher, not "Float" voltage, so that is only hit briefly not held there.
I understand higher voltages held for a period of time cause the battery to continue charging to a higher SoC, don't think that is good for them.
(i.e. "After that go back to 54.5 or 55V and see if it maintain 100% after a charge.", sounds like boost to 57V followed by float at 54.5)
 
So the battery vendor (ESS) really came through today. Their tech spent a couple hours on the phone with me and we upgraded the PACE bms firmware to the most recent. It was on 1.0.3, and the new version is 1.0.5. After a full discharge and charge, ALL readings look correct now.

As others have mentioned previously, an interesting takeaway from all this is that the cool "Maintain battery state of charge" feature in Solar Assistant should really be based on actual battery voltage, not SOC. If that was the case then it wouldn't matter what soc was being reported. This is especially true if the BMS is emulated by SA. I may start another thread on this topic to solicit feedback on this.
 
Jazzmonger said:
So the battery vendor (ESS) really came through today. Their tech spent a couple hours on the phone with me and we upgraded the PACE bms firmware to the most recent. It was on 1.0.3, and the new version is 1.0.5. After a full discharge and charge, ALL readings look correct now.

As others have mentioned previously, an interesting takeaway from all this is that the cool "Maintain battery state of charge" feature in Solar Assistant should really be based on actual battery voltage, not SOC. If that was the case then it wouldn't matter what soc was being reported. This is especially true if the BMS is emulated by SA. I may start another thread on this topic to solicit feedback on this.
Click to expand...
Hi. Help me please. Сan you tell how to update bms firmware and where to get it ?
I bought this (very, very similar) battery (2E-LFP48100). It charges from my UPS to 55.3V and shows 94% SOC at the end of charging (all cells are charged almost equally 3.439-3.475, except for one - 3.404). But there is a problem. Immediately after reaching 94%, the SOC starts to drop by about 1% every day. I waited for the SOC to drop to 65% and tested the battery for capacity - everything is fine, it holds as expected (it worked for a long time with SOC 0%). What could it be? In fact, it doesn’t really matter to me what SOC it shows, the main thing is that there would be no daily drop in SOC. Thanks and sorry for the bad English (I'm from Ukraine).
 
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