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jonr avatar image
jonr asked

SOC jumps to 100%

Hello, I have installed a 500a b/t smart shunt. I have a new 100ah LiFePo battery. Each day the smart shunt shoes the battery jumping back to 100% soc, at around 9am. This morning it had dropped to 77% overnight, then the sun got on the solar panel with the Victron mppt 100/20 and suddenly the soc reached 100% immediately. Have I got some settings wrong? Screen shot of history today and of settings.screenshot-20230421-094612.jpgscreenshot-20230421-095804.jpgImage Caption

SOC
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4 Answers
klim8skeptic avatar image
klim8skeptic answered ·

@JonR have a look at this how to set up your BMV video.

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jonr avatar image jonr commented ·
Hi Klim, this is the same information as contained in the setup guide from victron. I followed their video guide for a lithium battery, which are the settings above. Their is no explanation as to why I would get such a big jump, other than " there is something not right"
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derrick thomas avatar image
derrick thomas answered ·

Peukert factor is too high, charged voltage too low, and tail current should be lower. Charged voltage is your main issue. This should be set .1 volts below abs voltage.

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jonr avatar image
jonr answered ·

The peukert is exactly what the video says, and certainly what victrons setup instructions say, and with the others. What do you suggest they should say?

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derrick thomas avatar image
derrick thomas answered ·

In my experience the peukert for lifepo4 is actually closer to 1.01 but it partly depends on the size of the bank and the highest current draw expected. The charged voltage however is the cause of your problem. 13.2 is right around resting voltage for 12v lifepo4, and if you have solar this can cause premature full SOC calibrations. I don't know what your battery manufacturer specs for charging voltages but certainly 13.2 is way to low. Most people are comfortable with 3.45 to 3.55 volts per cell max charge voltage which would be 13.8 to 14.2. definitely don't go higher than 3.65 per cell. Say for example you set the abs volts to 14, then you want charged voltage set at 13.9 and tail current for lifepo4 can be set at 1%. If you set tail current too high and charged voltage too low you are not allowing any time for balancing at the top end.

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jonr avatar image jonr commented ·
Thank you derrick, that is very helpful. My battery data sheet says charge voltage 14.6v + or - 0.2v, so should I set it at 14.6 in the app, and drop the tail current to 1%?
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pwfarnell avatar image pwfarnell jonr commented ·
Set it to 0.1V below what your charger actually charges at, if your charger is 14.6V then use 14.5V on the shunt, if your charger is 14.2V then use 14.1V. The setting on the shunt does not fix the charging voltage, it is used to indicate to the shunt when the battery is being charged.
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derrick thomas avatar image derrick thomas jonr commented ·
If it were me (take at your own risk) I would set charge(abs) volts to 14.4 in the MPPT and also inverter or any other charging devices you may have, set float voltage to 13.8. set the charged volts to 14.3 in the shunt with a tail current of 1%, peukert of 1.02 and charge efficiency of .98. That's a good place to start and should get you back on track with the SOC after a good charge cycle.
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