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michal avatar image
michal asked

BMV 700 SOC and Capacity readings

Hi, I'am using BMV 700 and Lead Acid batteries 500Ah. In BMV I configured capacity 490Ah. My understanding is that 490Ah is 100% SOC thus e.g. 50% is 245Ah. But when BMV indicates 50% SOC it shows consumed capacity approx -290Ah. So what is the level of discharge: 50% or approx 60% ? I used both auto and also manual synchronization but behaviour is still the same. Discharging is slow and equal over the time in average 10Amps with some peaks to start the fridge. Please explain and provide more detail how BMV is performig its calculations. Thank you.

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3 Answers
Martijn Coster (Victron Energy Staff) avatar image
Martijn Coster (Victron Energy Staff) answered ·

@Michal please read the section on Peukert in the manual

chapter 3.3 page 13

https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE-PT-IT.pdf


best regards

Martijn Coster
Victron Energy

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michal avatar image michal commented ·

Martijn, thks. but I'am still confused. Let see this example: 500AH battery and Peukert coef. 1.1.

When discharging with 10A for 10 hours. Readings on BMV will be SOC=80% and Ah consumed= -126Ah

When discharging with 100A for 1 hour. Readings on BMV will be SOC=80% and Ah consumed= -158Ah

So the real remaining capacity will be 374Ah resp. 342Ah. But SOC is not 80%. It should be also 'compensated' by Peukert calculation.

I was expecting that in above example BMV will show SOC 74.8% resp. 68.4%

If the battery would be drained by very high current it could became empty but SOC reading on BMV will be still high.

I'am using BMV to protect from deep discharge and SOC reading looks like a not good choice and to drive relay by Ah consumed is not possible :-(

Where I'am wrong in my thinking? :-)

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Paul B avatar image
Paul B answered ·

I agree with Martijn

However

Its MUCH MUCH easier to set these up with a Bluetooh dongle attached to the BMS700 and easier to view the output screens as well


plus it gets updated to the latest FW as well

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michal avatar image
michal answered ·


@Martijn Coster (Victron Energy Staff), thks. but I'am still confused. Let see this example: 500AH battery and Peukert coef. 1.1.

When discharging with 10A for 10 hours. Readings on BMV will be SOC=80% and Ah consumed= -126Ah

When discharging with 100A for 1 hour. Readings on BMV will be SOC=80% and Ah consumed= -158Ah

So the real remaining capacity will be 374Ah resp. 342Ah. But SOC is not 80%. It should be also 'compensated' by Peukert calculation.

I was expecting that in above example BMV will show SOC 74.8% resp. 68.4%

If the battery would be drained by very high current it could became empty but SOC reading on BMV will be still high.

I'am using BMV to protect from deep discharge and SOC reading looks like a not good choice and to drive relay by Ah consumed is not possible :-(

Where I'am wrong in my thinking? :-)

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