Why is my SOC continually falling when my batteries are fully charged ?

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dave-bax asked Mar 9, '22

Why is my SOC continually falling when my batteries are fully charged ?

My BMV-712 Smart has never worked from the day it was installed (by others) when it comes to telling me what my SOC is. I have two 100Ah Li ion batteries connected in my car which is what the BMV should be reading for me. After we start at 100% and use the car fridge and other accessories the batteries decrease and the SOC gets lower, but then as I drive around and the batteries recharge to 100% from the alternator the SOC continues to drop and drop and drop due to whatever accessories I have running. Why can my BMV not recognise that the car batteries have been fully recharged and show me 100% SOC again ? Isn't that the whole point of the BMV ? Is it just a setting that needs changing or has the auto-electrician wired it wrong ?

Screenshots of the settings are shown below.

SOC

victron1.png (218.7 KiB)

victron2.png (206.2 KiB)

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Answer 1 · 2022-03-09T05:41:33Z

David answered · Mar 09, 2022 at 05:41 AM

When you have the car started and it charging, can you see the current going into the batteries in the app?

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dave-bax commented · Mar 09, 2022 at 11:13 PM

No the app does not show the alternator current flowing in to the batteries, should it ??

It just shows the amps getting drawn out of it by the fridge, and other accessories I connect.

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dave-bax dave-bax commented · Mar 14, 2022 at 08:54 PM

Mate should I be able to see the alternator current on the BMV ? This is an important question for me and could be the answer to my problems.

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Answer 2 · 2022-03-09T06:27:08Z

bathnm answered · Mar 09, 2022 at 06:27 AM

A schematic would be useful. When this happens, usually the charge source is connected to the wrong side of the shunt, and therefore it's current is not seen by the shunt, The battery and only the battery should be on that side of the shunt, and the charge source and all loads on the other side of the shunt. If you are using the chassis to supply the ground/negative it should be on the load side of the shunt.

I would also disable battery starts synchronised. If you have any battery switch which disconnects the shunts power when the batteries are isolated. When switched back on you are not guaranteed to have a 100% full battery.

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dave-bax commented · Mar 09, 2022 at 11:15 PM

Thank you for this advice, I will definitely look in to this.

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Answer 3 · 2022-03-09T08:49:26Z

johnny-brusevold answered · Mar 09, 2022 at 08:49 AM

@Dave Bax

I'm pretty sure the Charged voltage is set too low @ 13.3V. On my BMV 712 it is set to 14.2V and works perfectly.

13.2V = cell voltage of 3,325 which is about 60% charged

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dave-bax commented · Mar 09, 2022 at 11:17 PM

Thank you, but I watched a Victron online video about the BMV 712 and they said the charge voltage should be 0.3V less than the battery's float voltage which in my case is 13.6. I could try putting in a high figure like yours though.

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