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prb avatar image
prb asked

100/50 mppt charging lithiums, flashing between 13.6 and 15.5v - problem???

Precharging lith batts with 100/50 mppt. Checked with app and saw rapid cycling between 13.5 and 15.5v. I don't know what this means? We properly set the mppt to lithium profile, absorption 14.2v, float 13.5v, voffset to 0.1v, absorption duration to fixed, time 2 hr, tail current off? I've included Chins requirements below. No error messages.

Charging Limit Voltage: 14.6V

Over Voltage Disconnect Voltage: 15V

Over Voltage Reconnect Voltage: 14.2V

Float Charging Voltage: 13.8V

Discharging

Low Voltage Disconnect Voltage: 10.8V

Low Voltage Reconnect Voltage: 11.6V

Under Voltage Warning Voltage: 12.4V


I don't understand why it is cycling. I have another batt charging from another different mppt which does not cycle at all.


MPPT SmartSolar
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Alexandra avatar image Alexandra ♦ commented ·
@Prb

Not sure if this is the issue in your case but have seen this on a battery whose bms was unhappy.

Is your battery able to take the 50amp charge current? Some of them aren't able to.

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prb avatar image prb Alexandra ♦ commented ·
Thank you all for commenting. Am direct charging from solar to batt, nothing adding or subtracting other than line loss and mppt efficiencies. Amperage dictated by weather, mppt set to 50 amps max. I'm thinking unhappy BMS too. I guess question is really about given the mppt settings as described can the mppt alone spike charging voltage to 15.5v (way past the 14.20v I've set) without the battery making it spike?
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Alexandra avatar image Alexandra ♦ prb commented ·
@Prb

It uses the battery as reference and tracks the power for the panel. The voltage will rise on the battery terminal side if there is nowhere for the produced power to go.

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prb avatar image prb Alexandra ♦ commented ·

So basically no. The BMS must be shutting down then re-engaging which would explain the cycling shown by mppt. last question, if we change only the absorption duration on the mppt to say 8 hrs (currently at 2) keeping all same settings would that make the mppt act differently in it's charging profile other than just extend duration? I.e; would not use less amps at 8 hrs as opposed to 2 hrs.


Thank you in advance for considering these questions.

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1 Answer
Paul B avatar image
Paul B answered ·

Without more information my guess is that your batteries BMS is turning off then back on then off again etc etc

This maybe caused by having a unbalanced cell thus the batteries BMS is turning the battery off or you maybe sending to much current to the battery. so to answer in more detail, please supply a wiring diagram and maybe some photos of the installation, the more info the better. even some screen shots of the smartsolars settings and some historical details (presuming that you have a smart solar and a Bluetooth connection

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