SOC Always Decreasing

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jjack811088 asked May 28, '19

SOC Always Decreasing

Connected to shore power the SOC goes down more everyday. The system hovers over 13.5. Would love any help I can get. The MPPT is inside the RV and the batteries are under the coach about 10ft away. I am using the biggest recommended size cables for everything. I am thinking about getting the Smart Battery Sense Sensor since they are not both in the same enclosure, but I thought the 712 would send the voltage and temp info across the network to the mppt. Anyway the SOC has never gone up without me having to sync it to do so.

506583637885

RV Setup

4X100AHU Battle Born Batteries LIthium

800 Watts Solar 4 200W 18V Panels in Parallel

CCGX

12/3000 Multi Plus

712BMS With Temp Sensor

150/85 MPPT Smart Controller

Multiplus-II MPPT Controllers BMS CCGX Color Control SOC

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chaptertoo commented · Jun 05, 2019 at 08:09 PM

I have a similar set up on my boat, 6 100ah lithium batteries, 230v Quattro, 110 3K multiplus, 990 watts of solar, and BMV-712, CCGX. While on Shore power, with batteries at 13.8V SOC drifts down from 100% to 90 over nite, continues down day after day while voltage remains at 13.8v. I have let it draw down to 0 over time.

Current draw is a pretty constant -2.8amps. Peukert set to 1.05, efficiency factor set to 98%, tail current set to 4%. If I switch battery monitor on teh color control to the quattro, SOC goes up from whatever is registered at the time to 100% over time. Or I manually sync SOC to 100%.

Seems like the same problem JJack811088 is experiencing. Any ideas?

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chaptertoo chaptertoo commented · Jun 18, 2019 at 09:32 PM

Problem solved. Dealer replaced teh BMV and the shunt. Works now, batteries at 100% while on Shore power, cycles through bulk, absorption and float as designed.

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wkirby answered · May 28, 2019 at 06:36 PM

I wonder if the zero current calibration is true? If there is absolutely zero load orcharge current by disconnecting everything from the load terminal of the shunt, does the BMV actually read zero? If not then it can be calibrated to do so.

If this is correct, then there must be a load current flowing which is causing the SOC to decrease.

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Modifications Space

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Answer 1 · 2019-05-28T15:35:41Z

wkirby answered · May 28, 2019 at 03:35 PM

Are you sure that the shunt is connected the correct way around? If it is connected backwards then charging current will be measured as discharge current and the SOC will decrease whilst charging.

Only the battery - should be connected to the Battery Only - side of the shunt. All loads and chargers should be connected to the Loads and Charger side of the shunt.
If any chargers or loads are connected directly to the battery - pole then they will not be counted by the BMV.

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jjack811088 commented · May 28, 2019 at 04:27 PM

I should have wrote that, but yes. Only the battery is connected to the battery side of the shunt and everything else is on the load side

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Answer 2 · 2019-05-28T19:20:35Z

jjack811088 answered · May 28, 2019 at 07:20 PM

I checked it Monday, but I will post a picture so you can verify.

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Answer 3 · 2019-05-29T05:07:35Z

JohnC answered · May 29, 2019 at 05:07 AM

Hi Jack. SOC is a calculated figure, and uses factors you have to determine and input to get good results.

From memory, for Li batts, I think a recommended start point for 'Peukert' is 1.05 and 'Round trip efficiency' 99%. In a perfect world they would both be unity.

If you have a regular downward drift of SOC, perhaps your Peukert is set too high, and/or RTE set too low. (Have I got that the right way round?)

Essentially you have to tell the BMV how imperfect your world is.. :)

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Answer 4 · 2019-06-06T23:02:08Z

jjack811088 answered · Jun 06, 2019 at 11:02 PM

I was able to fix the problem. No the shunt was not installed backwards and there were no loads on the battery side of the shunt. I simply disconnected everything on the load side of the shunt and synchronized my BMS to zero. When I hooked everything back up I was getting positive charge and it has worked correctly ever since. I'm not sure why it I was thinking there was a load. Hope this helps someone else.

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chaptertoo commented · Jun 07, 2019 at 08:12 PM

Could you clarify what "sync your bms to 0" means? Did you sync soc to 0?

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remi commented · Oct 19, 2021 at 03:50 PM

Hello jjack,

I have been experiencing a decreasing SOC trend for about 3 weeks. This after the system worked perfectly for about a year. Will be interested in how you synced your "BMS to xero"! Perhaps you are referring to the BMV? My system doesnt have a BMV and the Pylontech BMS acts as battery monitor, so how to sync the Pylontech BMS?

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Answer 5 · 2022-05-26T19:45:01Z

askdba answered · May 26, 2022 at 07:45 PM

I am in the same boat :) On my sailboat previously same system with BMV712 none smart version of the battery monitor I’ve always had floating to %100 of charge when connected to shore. I’ve done an upgrade to BMV712 with two shunt ports one that goes to Service the other Start battery now my SOC keeps decreasing with 1-1,5 Amp range which is normal due to fridge and other usage.

I have tried all suggestions here in this post still the same after few days SOC goes below %70.

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