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goncalo avatar image
goncalo asked

Keep Batteries Charged not reaching 100% - not using Bulk?

I have 18 LFP cells in series, connected to a Multiplus-II 48/5000/70-50, but have not installed solar PV yet. I'm trying to fully charge the batteries but unsuccessfully. It seems that both Scheduled Charging and Keep Batteries Charged only use the "Float" setting without going through the cycle "Bulk -> Absorption -> Float". What seems to be happening is that at the Float voltage (60.3V for my system, 3.35V per cell), the charging current quickly decreases and the battery does not go higher than 68% SoC (as calculated by the SmartShunt that is also installed in the system).

Is there a way to force the Multiplus into Bulk charging mode?

Maybe this is a problem with my settings, here is a summary (values in parenthesis per cell). Please let me know if more information is needed:

  • DC Input Low Shutdown: 52.0V (2.88)
  • ESS Cut-off Discharge: 54.0V (3.00)
  • Absorption: 61.2V (3.40) 2h time
  • Float: 60.3V (3.35)
  • ESS Sustain: 60.3V (3.35)
battery chargingmultiplus ve.bus
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2 Answers
nickdb avatar image
nickdb answered ·

Why is your sustain voltage so high? That's not right.

Are these voltages not pushing the limits of the multi's charger?

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goncalo avatar image goncalo commented ·
It probably is too high indeed. What do you suggest the sustain voltage should be?


Yes, a bit higher than usual, but within the limits of the multi. I’ve seen examples of people with the same amount of LFP cells in series with no problems.

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nickdb avatar image nickdb ♦♦ goncalo commented ·

If I compare to pylon and others, sustain seems to be around 2 to 3V above dynamic cutoff depending on pack voltage.

So thats around 3.125 to 3.2V per cell on the batteries we use.


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goncalo avatar image goncalo nickdb ♦♦ commented ·
Thank you for the help! I’ll change the Sustain voltage.

Any thought regarding the main question?

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nickdb avatar image nickdb ♦♦ goncalo commented ·

It really shouldn't matter. If ESS is working fine (it doesn't seem to be due to settings) then it will charge correctly and vary between bulk/absorb depending on PV and charge level.

Lithium doesn't really do the typical bulk/absorb/float cycle.


edit: I take it your pack isn't managed by a BMS? Usually this just tells the multi what it wants and everything follows.

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goncalo avatar image
goncalo answered ·

In case someone reads this coming from google or something, the problem was fixed by updating the Multiplus's firmware to the latest version. Lesson learned for the future: keep the software up to date!

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