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brian49 avatar image
brian49 asked

How long should it take to recharge my lithium battery?

Returns to 100% within minutes? It doesn't make sense!

We recently installed a lithium system. 200ah battery, dc to dc charger, ac to dc charger, 420 watt solar panels with an MPPT 100/30 Charger and a 2000w inverter. We are still testing it out and getting familiar with it. Last night we used the inverter and we also ran small fridge. This morning the bmv_712 monitor displayed 71% state of charge. Within 20 minutes on a very cloudy morning the state of charge returned to 100%. This doesn't seem right. Is there something wrong with the system or is it normal for the system to return to 100% so quickly?.....again this morning we ran the system down to 95% and within 3 minutes the system returned to 100%.

I would really appreciate some feedback.

Cheers


Lithium Battery
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Trevor Bird avatar image
Trevor Bird answered ·

Hello @Brian49 . Did you set up the BMV712 with the parameters for the system? The BMV712 will declare the system at 100% when the charging current is a 4% of the 1C charge rate ( in your case 8 amps), the “Charged voltage” is reached and it has been that way for 3 minutes. If the charged voltage is set too low it will sync to 100% early. Set the “charged voltage” setting about 0.2volt below the absorption voltage of the solar charger. Hopefully that will allow the BMV712 to track well. Something is out because if you were at 70% of capacity (60Ah used) it would take 2 hours flat out for the solar charger to bring them back to 100%. (2 x 30 amp)

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brian49 answered ·

Hi Trevor, thanks for your response however your explanation is beyond my knowledge. Can you explain in detail what I need to do to hopefully fix the problem.

Many thanks

Ps. The fellow who installed it said I should use the Victron default settings for the lithium battery.

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kevgermany avatar image kevgermany ♦♦ commented ·

712 sets 100% based on measured battery voltage, current and how long it's been at the low current/high voltage combined. Clouds trick it as they cut the charge current.

As this is subject to your local conditions, some tuning of the 712 is needed.

Connect to the BMV using Bluetooth in Victron connect

Settings

Find charge detection time, this can be increased, if it's often cloudy try 10 minutes or more

Increase charged voltage as above

Decrease the 4% setting, try 3%.

Check battery capacity is actually set to 200.

Also check all the battery, shunt and MPPT wiring connections and cable sizes. High resistance can cause wrong readings.

It would help if you can show use the MPPT values at sun and at the point where the bmv shows 100%

The MPPT is not controlled by the monitor, so your battery will charge properly, even if the BMV shows 100%

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Trevor Bird avatar image
Trevor Bird answered ·

Hello, You will need a the Victron Connect app on your phone. It allows bluetooth access to the BMV712 so you can set it up for your system. When you have that so you can communicate with the BMV712 you should touch the cog symbol in the upper right hand side of the screen. You can now put in the various parmeters for your particularl system like 200Ah etc. That way the BMV712 knows how big the system is and can track the status of the batteries accordingly.

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brian49 answered ·

Hi I have the BMV712 on both my phone and my Android tablet. The app shows the 200ah battery already. I note that there is a setting "tail current" of 4%. Does that have anything to do with the problem? I will take a photo of the setting and post it


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Trevor Bird avatar image
Trevor Bird answered ·

Hello @Brian49 ….. your charged voltage setting is too low. Make it 14.2 volts to start with. Make the peukert exponent 1.05. Make the charge efficiency 98%.

These numbers will get you close to where you need to be. The smartshunt was using a lower voltage to deem the battery fully charged. That is why it was happening way too early.

Good luck with it.

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brian49 answered ·

Many thanks Trevor....changes made

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brian49 answered ·

Trevor, sitting in the sun watching state of charge going up in increments of 1 (one). That seems to have fixed the problem. Many thanks for your advice!

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Trevor Bird answered ·

The goal is for the BMV to track the battery so that it gets to about 95-99% and then synchronises to 100% when the conditions for 100% charge are met.

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