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ben-barker avatar image
ben-barker asked

BMV SoC and power loss

I have a BMV-700 to monitor a battery. I know it has some non-volatile storage, since it retains settings. However, if the monitor is disconnected and then reconnected, battery SoC resets to 100%


Two questions:


1) Is there a way to retain the last know SoC?

2) If not, what is the mechanism by which the BMV will get back into sync with reality....?



BMV Battery Monitor
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3 Answers
nickdb avatar image
nickdb answered ·

You can disable the setting "Battery starts synchronised" which will stop the behaviour of starting at 100%.

You can also manually set the SOC.

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ben-barker answered ·

Ah OK

So, from the manual:

"

When set to ON, the battery monitor will consider itself synchronized when powered up, resulting in a state of charge of 100%. If set to OFF, the battery monitor will consider itself un-synchronized when powered up, resulting in a state of charge that is unknown until the first actual synchronization.

"


Synchronisation will occur automatically when the BMV detects the battery is fully charged


https://www.victronenergy.com/media/pg/SmartShunt/en/operation.html#UUID-b46e8c9c-ade6-43c6-a192-d7fcd84e12a7


However, the system will never simply assume the last know SoC on power restore

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nickdb avatar image nickdb ♦♦ commented ·
Indeed, but if you know what it was approximately, you can set it yourself.

There's always a trade off and it depends which is the least inconvenient option.

Ultimately you'd want to try avoid the disconnects.



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ben-barker avatar image ben-barker nickdb ♦♦ commented ·
Yep - in our use case the battery fairly often discharges completely, so power is lost. Our old TR16 Chinese BVM could store the last known SoC - so when it started charging again it would remember "0%"


We can't use that meter any more since it has little if any formal documentation - but that particular feature was extremely useful! Given the BVM-700 does have some non voltaile memory it would be really useful if they added this functionality as an option!

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nickdb avatar image nickdb ♦♦ ben-barker commented ·
I hear you. I suspect there is an architectural reason or perhaps they are assuming that if the device is off for any significant period that storing it probably isn’t helpful and a proper sync is needed.
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ben-barker avatar image
ben-barker answered ·

Ah....the smartShunt seems to have this option, but not it seems the BVM-700:

https://www.victronenergy.com/media/pg/SmartShunt/en/all-features-and-settings.html

7.2.10. Battery SOC on reset

This setting determines the behaviour of the state of charge (SOC) value following a battery monitor reset. A reset occurs when the battery monitor is powered down and subsequently powered up again. This occurs during initial installation or disconnection, such as on a boat when the DC system is disconnected via the main DC breaker.

The "Battery SOC on reset" setting has the following modes:

  • Keep SOC - The state of charge is set to its last known value. This is the default mode. In this mode, the battery monitor regularly stores the state of charge and, after losing power, resumes from the last known state of charge.

  • Clear - The state of charge remains unknown until the synchronization levels are reached and synchronization occurs.

  • Set to 100% - The state of charge is set to 100%.


It looks though like this option is not available on the BVM-700...? In our use case this is quite key, so I need to work out whether we should return our BVM-700's for the BMV712 (I chose the 700 initially as we explicitly didn't want bluetooth, but I can just disable it if needed...

Alternatively might this functionality be available in a BVM-700 firmware update?


Does anyone know if the shunt itself is identical - in other words, can I simply swap out the BMV-700 head unit for a BMV-712 head unit, and keep the original shunt?


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nickdb avatar image nickdb ♦♦ commented ·
The bmv smart 712 also supports this. So probably a limitation on the older device. Upgrade time ;)
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ben-barker avatar image ben-barker nickdb ♦♦ commented ·
Yep - I think that is what I will do. Do you happen to know either of the following:


1) Is the shunt the same? It simplifies the swap out if I can just change the head unit....

2) I wonder if anyone sells the head units on their own...(very closely linked to (1))


Cheers!

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Rebecca avatar image Rebecca nickdb ♦♦ commented ·
Excuse me, but how do I update it? I have the same problem.
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