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JJack811088 avatar image

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


MPPT - Solar Charge ControllerMultiplus-IICCGX Color ControlBMSSOC
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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?


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.

5 Answers
WKirby avatar image

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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JJack811088 avatar image

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

JohnC avatar image

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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JJack811088 avatar image

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

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WKirby avatar image

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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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