VRM showing wrong SOC

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Trung asked Apr 10, '22

VRM showing wrong SOC

Hi all

I have got a bit of a problem at the moment - perhaps an expert out there can help me with this issue.

Setup: Smart MPPT-150/30, Multiplus (MP)II - 5KVA, Cerbo GX, DIY Lifpo4 battery pack - 12KWh.

Problem: The SOC on VRM is not showing what it is suppose to be. After grid charging of battery to SOC of 95%. The input AC was then disconnected. The SOC has remained at 95% since.

VRM has been showing SOC 95% irrespective of actual battery voltage. This is then stopping charging of batter from MPPT and also from grid via MPII.

No problem whatsoever running this setup at all - Except until yesterday (09/04/2022 to present time)

Tried:

1) Disconncted and reconnected all - MPII & Battery Pack, MPPT and Cerbo GX - NO change.

2) Rebooting Cerbo GX via Remote Console - NO change.

3) Rebooted MPII and grid connection - NO change,

4) Increase Bulk and Float voltage to that higher than Battery Management System (BMS) - battery charged for a small increment due to the increase in MPPT Bulk & Float voltage - other than that NO change.

5) Applied continuous AC load - Battery voltage reduced due to load but SOC on VRM still showing 95%.

6) Applied AC load to drain battery and for BMS to restart - battery voltage dropped, BMS restarted but SOC still at 95%. As you can see on the screen shots Battery Voltage and SOC is in the same parameter box or window.

7) Checked for latest firmware - currently running latest firmware.

8) Changing Battery Monitor in Remote Console to Automatic and MultiplusII - NO Change.

Any assistance is much appreciated.

Many thanks!

Trung.

Screen shot 1 - SOC at 96% with No AC load. This then prevents the MPPT from charging the batteries (at 52.28V - SOC should about 50% - BMS showing 50.3% - connected directly to lifepo4 battery). At 50.3% - MPPT should kick in with the lower battery voltage and actual SOC.

Screen short 2 - SOC at 96% with AC load - SOC should reduce with AC load but it just stays static. MPPT kick in due to AC load / draw (but it should be charging anyway due to low SOC/Voltage).

VRM SOC

vrm1.jpg (146.3 KiB)

vrm2.jpg (156.4 KiB)

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Answer 1 · 2022-04-10T10:40:44Z

wkirby answered · Apr 10, 2022 at 10:40 AM

That SOC measurement is coming from the MultiPlus if I understand your system correctly.
This measurement from inside the MultiPlus cannot measure current from the MPPT, so charge current from the MPPT will not be counted into the battery.
The SOC reading will not prevent the battery from charging. The MPPT charger and MultiPlus charger charge up to their programmed target Voltages and it's these Voltage limits which slow and stop the charging. If your battery is estimated to be around 50% SOC and it stops charging, then the Voltage limit is probably too low. DIY LiFePO4 battery would probably 3.2V per cell, so maybe 3.5V per cell full charge which would result in an absorb Voltage setting of 56.8V.
52.28V is 3.268V per cell which is nowhere near full.

hen you have multiple charging sources, then a BMV or Smartshunt is absolutely ideal for tracking all energy into and out of the battery and then the SOC estimate will be much more realistic.

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Trung commented · Apr 10, 2022 at 10:55 AM

Hi Wkirby

Many thanks for your comments and reply to my query/problem.

I haven't changed the upper or lower battery charging parameters for about 11months now - a bit of fiddling when I set up the DIY battery pack initially but, I left it once it was running well. So, it has been running really well for the last 11months. It was only yesterday since things went a bit south and the SOC was stuck at 95%.???

I have tried and disconnect the whole system and then connect everything back for a complete system reconnect - I had hoped when this happened, the MPII voltage reading would be closer to the BMS. However, this never happened.

Since the SOC is at 95%, the MPII is not charging the battery pack either. I have disconnected this completely was well - but NO change,

Apart from charging my batteries up to 95% SOC somehow and then connect everything back together again - so that the SOC is representative of the battery SOC (as measured by the BMS), I am a bit stuck on what to do??

Many thanks again...

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kevgermany ♦♦ Trung commented · Apr 10, 2022 at 11:26 AM

As @WKirby said SOC does not affect charging.

With your setup you can ignore SOC.

Try checking your AC in connections/fuses/trips. Also please post the charge settings in the multiplus and MPPT.

Also check your assistants. There's one that can ignore AC input.

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Trung kevgermany ♦♦ commented · Apr 10, 2022 at 01:07 PM

Hi evgermany

Fuses all OK. No trips.

MPII and MPPT parameters as attached - they are fairly conservative.

I have noticed it is using / showing the MPPT voltage instead of Battery Voltage.

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mppt-1.jpg (152.3 KiB)

mpii-original.jpg (76.5 KiB)

JohnC ♦ Trung commented · Apr 10, 2022 at 12:04 PM

@TrungT

I would turn the Multi SOC off completely. It's just distracting you.

You mention a Voltage discrepancy between the Multi and the BMS. What about that reported by the mppt? It's possible to arrange a 'system' V with DVCC, but if the BMS can't communicate then it won't be included. But if you have V issues then you really must sort that out as a priority. Especially with Li batts.

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Trung JohnC ♦ commented · Apr 10, 2022 at 01:20 PM

Hi JohnC

Many thanks for your comms/msg.

MPPT = 58V and BMS = 52V - MBS cant communicate to MPII.

It seems to be reading V from MPPT and not BMS and battery voltage?

I have also tried to turn the MPII Battery SOC reading off - but, again, hasn't solved the issue - its taking the MPPT voltage.

Any comments welcomed.

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1649596719348.png (95.7 KiB)

JohnC ♦ Trung commented · Apr 10, 2022 at 02:22 PM

@TrungT

That V-difference suggests the BMS has isolated the batts away from the available charge. And in your earlier shots, showing what happens when the BMS is allowing discharge. Your issue appears to be with the BMS. The Multi's SOC has no say in any of this, ignore it, it's wrong anyway.

I'm actually surprised you have such high V settings in the chargers with what you say your batts need. Why so?

And as an aside, with a grid supply, best to untick the 'Weak AC input'. That's usually only necessary with mongrel gensets, and worsens the ac power factor.

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Trung JohnC ♦ commented · Apr 10, 2022 at 03:26 PM

Hi JohnC

I have been playing about with the Vs. Prior to this issue, my Float = 55V and Abs = 56V. I find doing normal charging, the V does jump around a little (with MPPT/MPII) and also with the long flat charge curve of Lifepo4, I make sure I push things a bit higher. 56V Div 16 = 3.5V each cell - so its not too bad.

I have disconnected the BMS, equalisation cable connectors to see if it makes a difference - plugged it all back and NO change. The BMS does charge the batteries when there is a AC load as well - so I think the BMS is OK. (I have unplugged and re-plugged everything previously as well)

I have been playing with the MPPT Absorption and Float Vs - increasing to higher than 56V to see if the system kicks back into life - but it doesn't. So increased Absorption in MPPT, MPII to 59V and also Float to 58V for a short while - my batteries true SOC is fairly low and so, it won't be too detriment.

I will turn the "Weak AC Input" off - thanks for that tip bit.

I have noticed that the MPII is "pulling" / using the MPPT Voltage instead of Battery Voltage AND also the SOC is stuck at 95%?? - As mentioned in an above entry - I turned the SOC measure function off in my MPII - but again, no luck.

Many thanks again for your comment/s.

Trung

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Trung Trung commented · Apr 10, 2022 at 03:33 PM

Hi JohnC..

Just another thing - went to isolate the MPPT, the voltage returns to the actual battery voltage BUT the SOC is stuck at 95% - and so the MPII doesn't charge the batteries?? So I am stuck on both accounts.

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kevgermany ♦♦ Trung commented · Apr 10, 2022 at 05:44 PM

How many times do we have to say that your system will not give an accurate SOC?

How many times do we have to say reported SOC does not affect charging?

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Trung kevgermany ♦♦ commented · Apr 10, 2022 at 06:19 PM

Hi Kevgermany

I understand the SOC is not accurate but it should move up and down with some degree of variation with charging and discharging - it should not stay put at 95% irrespective !! I was happy with the variation previously - that is not the question here.

I also understand that the SOC may not effect charging of the batteries but, as it stands at the moment, this is the only known variable that has changed in the last 11 months that I can confirm. It may completely be something different but, I have not found that thing yet.

From your advice, I have checked for trips and or any blown fuses - all that is OK. I do have any assistants either.

I have done about another 12 things to get to the bottom of the issue but have not bottomed it out.

Many thanks again..

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