250 ah lithium goes to low 10v too fast, bmv 702 shows 60%

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gilles asked Feb 6, '22

250 ah lithium goes to low 10v too fast, bmv 702 shows 60%

Hi, i have a 250 ah Lithium , a multiplus compact 800 va , an Orion 30 A monitored with a BMV 702.

I dont have any solar panel on my RV yet.

The problem is according to the bmv , i have 60 % of energy left but the battery is almost at 10 V and the bms is shutting down. I was running a fridge (150W) for 4hours , a router (20W), a few lights(20W), a computer(30W) for an average maximum of 200W. The problem appereared when i started to put the fridge on the 220V inverter to save some propane.

After a few hours , with that fridge on i was on alarm with 10v.

I think there is a problem with the bmv synchonisation but still i dont get it.

Maybe it is because of the way voltage drops with lithium , and the fridge is killing the battery too fast. I dont know.

Maybe i was fooled by the BMV. i will try to charge the battery to 100 % and the SYnc the bmv manually.

if someone sees something that i dont see.

BMV Battery Monitor SOC

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klim8skeptic ♦ commented · Feb 06, 2022 at 09:55 AM

Absorption fridges suck. They do not have a thermostat operational whilst running of DC.

Bin that fridge, or run solely via gas\mains power.

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gilles commented · Feb 06, 2022 at 10:01 AM

When the battery was almost at 10V , the BMV said -110 Ah consummed. So i dont get it, my battery is 250 Ah !

Also the fridge consumption is well recorded by the BMV because it said -150 w when th e fridge was on .

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klim8skeptic ♦ gilles commented · Feb 06, 2022 at 10:10 AM

3 comments.

Your sure that your battery was fully charged?

Your sure that your bmv has been set up correctly?

Absorption fridges suck.

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Modifications Space

Node Red Space

Answer 1 · 2022-02-06T09:50:01Z

Matthias Lange - DE answered · Feb 06, 2022 at 09:50 AM

Is the shunt wired correctly?
Only the shunt is connected to the battery negative all other negative have to be connected to the shunt.

Can you show us the settings of the BMV?
Maybe some pictures of the wiring.

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Answer 2 · 2022-02-06T22:14:23Z

gilles answered · Feb 06, 2022 at 10:14 PM

Yep, i think the BMV was not set up entirly. I changed a few things with the smart dongle connected to the BMV 702 ( see picture)

I will try to charge the battery until 14V and then manually set the current state-of-charge to 100%.

I think my battery is rated for a maximum of 14.6 V. But i guess it is not that good to go all the way to the maximum.

I think the wiring is fine, only the negative of the battery on the battery only side of the shunt, the rest of the negatives on Load and charger side of the shunt

Yeah, the peukert exponent was 1.25, the charged voltage 13.2 V, and maybe that fridge made it worst on top of that, with an incorrect SOC also at the begining.

screenshot-2022-02-06-22-26-13-191-comvictronenerg.png (91.5 KiB)

screenshot-2022-02-06-16-58-49-405-comvictronenerg.png (121.7 KiB)

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Answer 3 · 2022-02-06T22:19:59Z

gilles answered · Feb 06, 2022 at 10:19 PM

here is the settings and the wiring too.

screenshot-2022-02-06-22-25-54-004-comvictronenerg.png (124.7 KiB)

screenshot-2022-02-06-16-59-36-985-comvictronenerg.png (60.8 KiB)

img-20211223-103508.jpg (2.3 MiB)

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Answer 4 · 2022-02-07T02:37:03Z

kevgermany answered · Feb 07, 2022 at 02:37 AM

No point in manually setting SOC. It will reset to 100% automatically based on reaching the charged voltage and the current dropping to tail current for charge detection time.

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Answer 5 · 2022-02-14T12:01:52Z

willk answered · Feb 14, 2022 at 12:01 PM

Could it be that your discharge floor is 50% which I believe is only for agm/gel/lead acid where 50% is usable.

I'm pretty sure for lithium it is generally 20% discharge floor or 80% of stated capacity (manufacturer dependent). This could explain why it is not utilising the full capacity. I had the same problem when setting my system up and this solved my problem.

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kevgermany ♦♦ commented · Feb 14, 2022 at 01:15 PM

afik, that's only used in the time to go calcs.

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