Read Voltage From Solar Panel - ADC Questions

[devonsc]

Hi,

Do you guys mind to give me some advice on how do I tap voltage the output voltage of the solar panel for ADC purposes? I'm building a boost DC/DC converter where the input of this circuit is being supplied by a solar panel.

By using a PIC microcontroller, I intend to perform some ADC set-up to read the output voltage of the solar panel to control my duty ratio of my DC/DC converter. Any advice?

Can I connect a small resistance value in series and pull a wire out from the end of the resistor for voltage reading? Is this good enough? Will this work?

Added after 48 minutes:

Would like to add on something here:

I've read about ADC using Vref. I'm not sure what it is for, do you guys mind to explain the need of the Vref? As I thought it the set-up of PIC will just take in voltage and convert to a digital level. Sorry, I'm very new in this. Mind helping? Please?

 

[flatulent]

Solar panels are frequently 12+ V output and you will have to get this down to the allowable range of your ADC. Use a resistive voltage divider. It should be high enough impedance to not waste power while low enough that the input bias current of your ADC does not cause 1 LSB error. For preventing damage of your ADC the open circuit solar output at maximum sun should be the value to use in calculating the divider ratio.

On the reference, the ADC does comparisons of the input with something called the reference. You can use your power supply but that is usually 5% variation from nominal. This may not cause you any real problem in your system.

 

[devonsc]

Solar panels are frequently 12+ V output and you will have to get this down to the allowable range of your ADC. Use a resistive voltage divider. It should be high enough impedance to not waste power while low enough that the input bias current of your ADC does not cause 1 LSB error. For preventing damage of your ADC the open circuit solar output at maximum sun should be the value to use in calculating the divider ratio.

The output of the solar panel that I will be using for this project varies from 4V to 10V. By the way, I'm still not sure what you mean by a resistive voltage divider, sorry. Real sorry. Does it mean that I'm suppose to first connect a small resistance value of resistor to the solar panel's output line to tap the voltage, then from there, I have a voltage divider, with one end to the ground, and another to the PIC analogue input?

On the reference, the ADC does comparisons of the input with something called the reference. You can use your power supply but that is usually 5% variation from nominal. This may not cause you any real problem in your system.

My first thought is to power up the PIC using the output voltage of the solar panel as well. Does it mean that I shouldn't do this? Any advice or ideas on how can I get it done if I were to remain powering up the PIC with the solar panel's output voltage? Thanks in advance....

 

[flatulent]

The resistive voltage divider is two resistors in series. One end of the string is to the solar output, the other end is to ground or circuit common, and the center is to your PIC ADC.

On powering your PIC, if you use a LDO linear you will have to operate the PIC at 3.5 V. If you use a switching converter you will have to use one that can accommodate the wide input range to produce your wanted output.

 

[devonsc]

The resistive voltage divider is two resistors in series. One end of the string is to the solar output, the other end is to ground or circuit common, and the center is to your PIC ADC.

But what I am trying to do at the same time while tapping the voltage for ADC to the PIC is applying the DC/DC converter circuit with the output voltage from the solar panel. If I were to do as mentioned, I will not be able to supply my DC/DC converter circuit, is this right?

On powering your PIC, if you use a LDO linear you will have to operate the PIC at 3.5 V. If you use a switching converter you will have to use one that can accommodate the wide input range to produce your wanted output.

Sorry but do you mind explaining what LDO is? Real sorry.

Real sorry if Im being unclear with my project that I am trying to carry out. Do you think I should briefly explain them in full here? Thanks in advance...

 

[barrybear]

You must remember to include a series diode in the feed from your solsr panel. This will prevent voltage flowing back in to the panel and damaging it.

Barrybear

 

[devonsc]

Hi there,

Do you guys mind checking for me if the following is the proper way for me to tap the voltage of a supply and divide it into half before applying it to my ADC input of my PIC microcontroller? (Assuming, R3 is my Load)

By the way, I have doubts though: Do I need to include a small resistance resistor at point A before tapping the voltage off the line? Someone told me to do that, but it seems that I can still manage to tap the voltage without the presence of a resistor at Point A. If I do need to include a resistor at Point A, do you mind explaining the purpose of it? Please?

Thanks in advance...

 

[srivatsan]

i am doing the same thing with little change. instead of a panel, i want to plot the solar cell I-V curve, without any manual intervention.
so i am desiging/fabricating a chip for that purpose. it includes ADC also.
i would like to know the need for DC/DC booster and PIC microcontroller.
in short, i would like to discuss the specific project with that individual. Is there a way that you can post your project objectives and the way to achieve it?
thanks a lot.
srivatsan

 

[devonsc]

Hi Srivatsan,

I guess my project differs from yours. Guess yours is way better, advance and for geniuses like you to develop Mine is just a normal-lousy project. I'm a newbie in electronics.

Anyway, briefly, this is what I am doing:

I intend to build a Battery Charger and Monitoring Unit, I call it. Where it will be used for charging lead acid batteries of 6V or 12V. I'm progressing it by dividing into a few portions.

a.) A boost DC/DC converter to step-up the output voltage of the solar panel to an appropriate level for charging purposes.

b.) An AC/DC converter to step-down and convert a 240V AC source to an appropriate DC level for charging purposes.

c.) The PIC microcontroller that I will be using would be used to control the PWM signal for my DC/DC converter, prevent overcharge, manipulate a LCD to display values of the ADC feedback.

I'm a newbie here, mind to give some advice if there is any flaws in my design? Any suggestions to enhance my project? Thanks a lot in advance...

 

[srivatsan]

Hi Devonsc,

WEll, I am not sure of genius stuff, ... interesting???.. yeah .. probably?!?!?!!!.....

I got to get this done probably before feb 1st week. i see your project ot be different and interesting.
I will get back with details very soon.
regards,
srivatsan

 

[IanP]

Straight answers regarding your circuit:

At point A you do not need additional resistor.
I would remove load resitor R3..it doesn't play any roll as you already have load of 2kΩ connected in parallel.
Also, you may add 5.1V zener diode and 100nF cap between ADC input and GND (0V). This will reduce potential noise and protect the input allowing only max 5.1V..

 

[yakroo]

What circuit charg 12V batt?

 

[nikhil_damle]

friends i dont think the output voltage of the solar pannel is analog in nature it gives a proportional output voltge. so no problem in that 0-5V or based on the pannel ADC input of pic can be used for scaling