question

ciphersix avatar image
ciphersix asked

BVM-712 SOC not accurate

This is my second season with the following setup:

  • WFCO-8955 Power Center
  • Victron BlueSolar MPPT 150/35
  • 3x Battleborn BB10013 100 Ah 12V LiFePO4 Deep Cycle Battery
  • Victron BMV-712 Battery Monitor
  • 3x KIT1010 90w Zamp Solar Panels

I have the BMV set exactly according to the battery website (see screenshot):

image007.png

https://battlebornbatteries.com/configure-victron-bmv-700-bluetooth-dongle/

The issue that I’ve always had is that the displayed SOC decreases much quicker than the actual SOC:

  • After connecting to shore power, the batteries will quickly charge and SOC will show 100%, but if the system remains connected to shore power for a day or two, the SOC will drop from 100% to as low as 80%, lower if connected longer.
  • When boondocking/drydocking, the SOC will eventually display 0% yet the batteries will continue to put out power for days, running the refrigerator, pump, lights, etc.

This leads me to think of these possible issues:

  • Wiring is incorrect. I've had the installer and battleborn/dragonfly check the wiring 3 times. Everything has been verified correct (see screenshots).image008.jpgimage004.jpg
  • The battery parameters for the BMV are not correct. This has been checked many times by battleborn/dragonfly.
  • The algorithm for SOC is not correct. I can't believe this is true since most people say how accurate this is.
  • The batteries have much more capacity than 3x100 aH=300 aH. If the battery bank was substantially higher, then this might explain why the SOC drops to 0% yet I still have power left in the batteries, but it wouldn't explain why the SOC drops even when connect to shore power.
  • There's something wrong with the WFCO-8955 charger. There is almost nothing to configure on this except the Li switch (which is correct).

As a possible fix, could I increase the battery capacity? Is this recommended?

Battleborn/Dragonfly says that the system must be completely charged and discharged to 0% 4-5 times before the BMV "learns" the true capacity of the batteries. I haven't seen this documented and so I don't understand how this would work. Is this true?

Anyone have any other ideas? I'd love for this to work, but with the current situation, the SOC is useless.

BMV Battery MonitorSOCaccuracy
image007.png (364.2 KiB)
image008.jpg (32.7 KiB)
image004.jpg (31.9 KiB)
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ciphersix avatar image ciphersix commented ·

Thanks for all the quick answers/follow-up questions!

@Mike Dorsett . I have not used a clamp ammeter, but this is something I could do. I assume that I would clamp around the load side (-) from the BMV and see that that current measurement matched what was being reported?

@Trevor Bird I don't have access to the device at this moment, so I can't check Settings>Misc, however I have factor reset the settings recently, so if this is the default, then it should have been set back, but the issue still persists.

@Matthias Lange - DE I have suspected that the charger might be to blame since it seems like it stops giving juice to the batteries before the BMV sees the 14.2V for 3 min. I normally have to charge it up with shore power, the SOC will say something like 80%, then I disconnect for a few minutes and reconnect and the SOC will finally sync to 100% in just about 4 min. I don't think I can change anything on this charger (WFCO-8955). Do you have an intelligent question that I can pose to the manufacturer, I'm not sure what to ask them.

@kevgermany I have not done this. The battery manufacturer told me to never mess with this. The tech indicated that there was some kind of risk. What is the procedure?

Thanks again all!

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5 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

The BMV does not "learn" anything about the battery - it operates from the parameters that it is given. it appears from the last 2 pic's that the wiring is correct. Have you used a clamp ammeter to measure the circuit currents under the various conditions?

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Trevor Bird avatar image
Trevor Bird answered ·

@ciphersix ….The operation of the BMV is fairly basic in concept but it seems in your case something fundamental is incorrect. The settings seems reasonable if the size of the battery bank is correct. Can you please confirm that in “Settings” when “Miscellaneous” is selected Current is set to 500 Amp and the sense voltage is set to 50mV. These are fundamental to the correct operation of the BMV and for some reason may have inadvertently been changed.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Maybe the float voltage of the charger is to low?!

In that case the battery has to supply the load after the charger switched from bulk to float.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
There is something to this. Charge state voltages look unsuitable for a Li battery..

Any one got a proper WFCO manual??

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kevgermany avatar image
kevgermany answered ·

Have you carried out the zero current calibration?

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kevgermany avatar image
kevgermany answered ·
Best follow the manual, section 4.2.1, parameter 09
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