Hi Guys,
I hope someone can point me in the right direction, I am completely lost! I have built a Solar Charge Controller based on a IRF4905 MOSFETchip. I use 2 x 3904 and one 3906 transistors to power the GATE of the MOSFET. I then use the PIC to switch the MOSFET ON and OFF on a specific voltage. I also have a LCD connected to the PIC that prints the solar and battery volts respectively using the 10 bit ADC through resistor divider networks.
Now with that said I am experiencing the following issue regarding the ADC values; When the solar panel is connected the reference voltage of the 78L05 chip comes down from 4.96V to about 4.66V and this creates a huge problem as the ADC reading is not correct due to the reference voltages fluctuating and this results in the charger not switching ON / OFF at the correct voltages. When I disconnect the solar panel supply the voltage returns to normal. I have tried various different techniques to solve this issue but I can't seem to find the solution.
I have tried the following:
1. Ground the solar panel directly to the battery (this seemed to work better but I still have a variance of about 0.15V).
2. tried different CAP values on the voltage divider networks (this made little to no difference at all).
3. Increased the CAP value on the 78L05 IC (this only works for a mere couple of seconds until the CAP is drained).
I don't know if I am missing something vary obvious in my design but I can't seem to figure this out, are there any experts out there that can assist me please!!! I attached my circuit from PDF export from Proteus to explain the circuit in more detail.
I hope someone can point me in the right direction, I am completely lost! I have built a Solar Charge Controller based on a IRF4905 MOSFETchip. I use 2 x 3904 and one 3906 transistors to power the GATE of the MOSFET. I then use the PIC to switch the MOSFET ON and OFF on a specific voltage. I also have a LCD connected to the PIC that prints the solar and battery volts respectively using the 10 bit ADC through resistor divider networks.
Now with that said I am experiencing the following issue regarding the ADC values; When the solar panel is connected the reference voltage of the 78L05 chip comes down from 4.96V to about 4.66V and this creates a huge problem as the ADC reading is not correct due to the reference voltages fluctuating and this results in the charger not switching ON / OFF at the correct voltages. When I disconnect the solar panel supply the voltage returns to normal. I have tried various different techniques to solve this issue but I can't seem to find the solution.
I have tried the following:
1. Ground the solar panel directly to the battery (this seemed to work better but I still have a variance of about 0.15V).
2. tried different CAP values on the voltage divider networks (this made little to no difference at all).
3. Increased the CAP value on the 78L05 IC (this only works for a mere couple of seconds until the CAP is drained).
I don't know if I am missing something vary obvious in my design but I can't seem to figure this out, are there any experts out there that can assist me please!!! I attached my circuit from PDF export from Proteus to explain the circuit in more detail.
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