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mark-f asked

How can I increase the charge voltage of my 48 volt lithium battery?

I have a Smart Solar 150/35 mppt Charging a 48 volt (16 cell) nominal system. At mid day with 52.5 volts indicated on battery voltage and In bulk mode charging I often see low (40w) current input. I am set on battery life for charge algorithm. Bank voltage of 53 volts is only 3.3 volts Per cell. I’d like to get a final charge closer to 55 - 56 volts. Can that be done?

Lithium Batteryvoltage
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Hi @Mark F. What’s your PV input voltage when this happens?

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The PV voltage is 59-61 volts

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And the amp readout can be as low as .5.

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@Mark F

The other thing to check would be battery settings on the mppt. Are the float and bill voltages set correctly? You can set customised voltages.

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3 Answers
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mark-f answered ·

I have never seen the charging change from bulk charging. I am set on the last setting (7?) for lithium batteries.

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mark-f answered ·

Thanks Murray and Alexandra,

Some more detail on my system; One SolarPower 320 watt panel. Sixteen SkyEnergy (CALB) 160 AH cells to make the 48 volt nominal bank.

I changed to User Defined Algorithm 1 and raised the voltage from 56 to 56.8 and it didn't seem to make a difference.


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I get a feeling your PV input voltage is too low and too close to the battery voltage to properly perform the maximum power point calculations. have you tried two of these panels in series?

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Sure, if the MPP Voltage of the PV array is less than the battery Voltage +1V then you'll not be able to get maximum power from the array.
If 59-61V is not the Maximum Power Point Voltageof the array, then the current will be low, thus low power.

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mark-f answered ·

I do have another panel that I can use to see if that will help. The PV voltage indicated from the MPPT is 59-61 volts. The battery voltage is 52-53 volts. That looks like 6 volt lower battery than the PV output. Is there a difference between the MPPT reading and the actual PV output?

Thanks

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Add the third panel in series to increase the PV Voltage.

If the Voltage at which the panels can produce their maximum power is less than 1V above the battery Voltage then you'll not see maximum power.
The MPPT can only scan for the best power point from open circuit Voltage down to 1V above the current battery Voltage.

Here is an example, 37V PV panel with a 24V battery (28V in absorb stage), shouldn't be a problem at all right?
Well, the client was having a similar experience to you. So, they doubled up their PV panels to 2 in series and then they did get full power. Why?
With their PV doubled up, the MPP Voltage of the PV array was showing at 50V (well above any battery Voltage). So for one panel The MPP Voltage would be 25V, which is actually below the battery Voltage.
The MPPT controller can scan for a maximum power point between open circuit Voltage and 1V above battery Voltage, but this might not necessarily be the maximum power point of the array.

The example I gave was for one panel (in series) on a 24V system. You are basically doubling everthing, 2 panels in series for a 48V system. The MPP Voltage will be doubled too. Once your battery Voltage rises abour 49V then the MPPT will not be able to scan the PV array down to a low enough Voltage to find the point of maximum power.

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