A very simple yet effective solar optimizer circuit can be made by employing a LM338 IC and a few opamps.

Let's understand the proposed circuit (solar optimizer) with the help of the following points:The figure shows an LM338 voltage regulator circuit which has a current control feature also in the form of the transistor BC547 connected across adjustment and ground pin of the IC.

Opamps Used as Comparators


The two opamps are configured as comparators. In fact many such stages may be incorporated for enhancing the effects.

In the present design A1's pin#3 preset is adjusted such that the output of A1 goes high when the sun shine intensity over the panel is about 20% less than the peak value.

Similarly, A2 stage is adjusted such that its output goes high when the sunshine is about 50% less than the peak value.

When A1 output goes high, RL#1 triggers connecting R2 in line with the circuit, disconnecting R1.

Initially at peak sun shine, R1 whose value is selected a lot lower, allows maximum current to reach the battery.

Circuit Diagram




When sunshine drops, voltage of the panel also drops and now we cannot afford to draw heavy current from the panel because that would bring down the voltage below 12V which might entirely stop the charging process.

Relay Changeover for Current Optimization


Therefore as explained above A1 comes into action and disconnects R1 and connects R2. R2 is selected at a higher value and allows only limited amount current to the battery such that the solar voltage does not crash below 15 vots, a level that's imperatively required at the input of LM338.

When the sunshine falls below the second set threshold, A2 activates RL#2 which in turn switches R3 to make the current to the battery even lower making sure that the voltage at the input of the LM338 never drops below 15V, yet the charging rate to the battery is always maintained to the nearest optimum levels.

If the opamp stages are increased with more number of relays and subsequent current control actions, the unit can be optimized with even better efficiency.

The above procedure charge the battery rapidly at high current during peak sunshines and lowers the current as the sun intensity over the panel drops, and correspondingly supplies the battery with the correct rated current such that the it gets fully charged at the end of the day.

What Happens with a Battery Which may not be Discharged?


Suppose in case the battery is not optimally discharged in order to go through the above process the next morning, the situation may be fatal to the battery, because the initial high current might have negative affects over the battery because it's yet to discharged to the specified ratings.

To check the above issue, a couple of more opamps are introduced, A3, A4, which monitor the voltage level of the battery and initiate the same actions as done by A1, A2, so that the current to the battery is optimized with respect to the voltage or the charge level present with the battery during that period of time.

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