Solar Battery Charger Design Help Needed

Solar Battery Charger Design Help Needed

Hi

I have designed this Solar Battery Charger. A 12V 75W Solar Panel will be used.

So, current will be max 6.25A

Charging current of SLA batteries is 10% of its Ah rating.

So, This charger can easily charge a 12V 40Ah battery.

1. Is there anything needs to be changed in the circuit ?

2. What should I connect to dsPIC33's VCAP/VDDCORE pin ?

This is better than transformer based battery charger which runs from mains because a 5A bulky transformer is eliminated and this can be used for mobile charging purpose.

Code has been written and tested on Proteus and it is working fine.

This is the panel that will be used.

**broken link removed**

I have ordered the Panel and PCB layout is being designed. I have taken Panel voltage as 20V for Buck Componnets calculation and it came to be 109uH and 58.7uF.

I want to decide the components before PCB layout is finalized.

3. What max voltage value I have to take for the Panel voltage, because I have to calculate Buck-Components based on this max voltage ?

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Looking at the mikroE Easy 24-33 v6 development board I connected a 10uF 63V from VCAP pin (pin 20 of dsPIC33) to GND.

Now please answer about panel voltage. I have assumed 12V Solar Panel Open Circuit voltage to be 20V and closed circuit voltage to ve 18V. I need exact voltage of the panel to find out the buck component values. I am using 100 KHz PWM but I am planning to use 100 uH 10.1A Inductor from Coilcraft. I will be using Hi-Temp Corlin Dublier Capacitor for the 10000uF and buck capacitor with high ripple current rating.

12V 75W Solar Panel

Click to expand...

I did tests on my PV panels rated 64W, thin film type.
Open circuit voltage 23.8 V.
Each panel delivered 3.4A to a 12V lead-acid battery (bright sun high in summer sky).

I found that I did not obtain 64W into a 12V battery. Expectations might lead me to think it should mean 5A. However in reality it was much less. The difference is because the load opposes with its own 12V. Therefore you might not get as many Amperes as you expect. DC-DC conversion will probably increase the amount, although you ought to run various tests to reveal what is within reach.

@BradTheRad

Ok.

I found that it is not good to use 12V Solar Panel because in my circuit 2.0V drop across bridge rectifier and if sunlight is not bright then Buck Converter will not get sufficient volatge and so I changed my circuit to use 24V Solar Panel which gives at lease 20V or above voltage. Actually I don't need that bridge rectifier as panel voltage is DC but I want to use the same circuit for mains voltage based charger where a 0-18V or 0-24V 5A transformer will be used. My design is fully automatic and it charges both 6V and 12V upto 40AH batteries.

Working is like this

When battery is not connected the dsPIC measures the battery voltage and as it is 0 it shuts of the PWM and displays "Connect Battery". When battery is connected it measures the battery voltage. If battery voltage is less than 6.5V then it takes it as 6V battery and if it is greater than 8V and less than 15V then it takes it as 12V battery. Then it checks the Buck input voltage or solar panel voltage. If voltage is good then it adjusts the duty of PWM to get 14.4V boost voltage or 13.8V trickle voltage at the output.

Here is the new and final circuit. I changed the LCD to 40x4 because I had to display progress bar of panel voltage and battery voltage.

A Calibration button is added. If calibration is not done then it will show only panel and battery voltages on Lcd and one has to vary the trim pots and adjust the adc input voltage and then press calibration button. This will register the calibrated values and use if for run mode.