question

fabrizio-baglio avatar image
fabrizio-baglio asked

Multi discharge stops at 70% charge

Setup:

Multi II 48/5000 AC input coupled with fronius 5kv grid connected and AC output 1 coupled with another fronius 5kv and AC output 2 connected to hws.

Basically after a overload detected and fixed the Multi would charge the battery as normal, it would trick the hot water system ones reaches the charge needed to start the relay and discharge the battery; than the hws reaches the temperature it stop(obviously) and the battery keeps discharging until reaches 67.5%, and stops discharging.

The battery monitor on the vrm show continues changes on battery voltages from 52v to 40v and it also changes the type of state from bulk to sustain.

I have checked al the connections, every single cell 3.2v, and only one shows 0.4 lower. Than I thought I lt may be that the batteries needed to be balanced, but Multi doesn't allow as it says that the charger is not ready. It charges if I set it up as keep the battery charged or if I change the min soc to higher value than 67%.


img-20220717-103056.jpg

Multiplus-IISOCess discharging
img-20220717-103056.jpg (8.1 MiB)
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

What batteries and BMS do you have?

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fabrizio-baglio avatar image fabrizio-baglio Matthias Lange - DE ♦ commented ·
Hi Mat, I have 16 prismatic lifepo4 3.2 cells 200ah, with relative bms for
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2 Answers
seb71 avatar image
seb71 answered ·

Your settings are bad.

every single cell 3.2v, and only one shows 0.4 lower.

That is a lot.

You will damage the battery with those settings (if not already damaged).

Can that BMS stop the discharge when a cell voltage or the battery voltage is low?


For LiFePO4 you want to charge to at most 3.6V and to discharge down to 3.0V (or higher).

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fabrizio-baglio avatar image fabrizio-baglio commented ·
What should I change?
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klim8skeptic avatar image klim8skeptic ♦ fabrizio-baglio commented ·

I watched this video today.

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seb71 avatar image
seb71 answered ·

What should I change?

That BMS can perform cell balancing? If yes, at what voltage?

Does if have low and high cell voltage/battery voltage protection? If yes, what voltages?


Without specific information, I would say to try these voltages for charging your 16 cell LiFePO4 battery:


Absorption:

Possibly between 56V and 56.8V.

Absolute maximum 57.6V (if the cells are perfectly balanced at the top).

Start with the lower values (even as low as 55.4V), until your cells get more balanced.

You might need to limit the charging current, too.


Float voltage: 53.6V.


ESS Dynamic cut off voltages:

0.005C = 49.50V

0.25C = 49.00V

0.7C = 48.50V

2C = 48.00V


ESS Sustain voltage: maybe 50.40V.

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fabrizio-baglio avatar image fabrizio-baglio commented ·
Thanks, and I think or the bms is damaged, and doesn't let discharge the battery, or the Multi has the Meter reader domaged.

When the Multi stoops to discharge and in sustain mode, voltage in Multi shows 40 but the multimeter shows 51....

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seb71 avatar image seb71 fabrizio-baglio commented ·

Multi shows 40 but the multimeter shows 51

Did you measured that voltage with the multimeter at the Multiplus battery wire bolts? If yes, then it sounds like there is something wrong with your Multiplus.

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fabrizio-baglio avatar image fabrizio-baglio seb71 commented ·

I'm top charging the battery with keep battery charged, I also adjusted the values you gave me.

Thanks man, I'll update you soon

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fabrizio-baglio avatar image fabrizio-baglio fabrizio-baglio commented ·
Seb all good, the Multi is working sweet. Thank you very much.

So basically after a fully charge of the battery all the cells were topped up and the Multi is discharging properly.


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fabrizio-baglio avatar image fabrizio-baglio seb71 commented ·

Seb all good, the Multi is working sweet. Thank you very much.

So basically after a fully charge of the battery all the cells were topped up and the Multi is discharging properly.

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