Solar charge controller in LTspice

[Ajay Renganathan]

Hello everyone.

I want to design a solar charge controller that can charge a lead acid battery of capacity 2 Ah, 12V, using a solar panel with 10 Wp capacity, 15V, and power an LED light of 5W rating when switched ON. I need to do hand calculations and select components and simulate the circuit using LTspice.

I am confused on how to go about doing this. I know the working of a basic Buck converter and I also know that PWM is used to make the pulse width large(and thus increase voltage) when initially charging the battery and later smaller(and this decrease voltage) when the battery is almost fully charged.

Considering that I am using LT spice, I need to use one of their own IC's which are readily available in India. I have some q's which I hope someone can answer:


* How do I go about selecting an appropriate one? I also don't know how to select the values of components such as resistors, inductors and capacitors. The only knowledge that I have is that a design equation would be given to me and based on this equation I would select components.

*What are hand calculations? How do I perform them?

*In an IC ,they usually give a circuit with components and their values in the data sheet. What's the use of these if I'm trying to design a charge controller based on my needs?

*Do all buck converters use PWM to step down the voltage?


I would be grateful if someone could answer my queries.
Thank you.

 

[BradtheRad]

Yes, you could say a buck converter uses PWM to step down the voltage.

See my posts in the thread linked below. They contain links to my interactive simulations of switched-coil converters.

https://www.edaboard.com/threads/268178/

You are the controller. Click the switch to start the first half of a cycle. Let up the switch to go on to the second half.

You can change values by right-clicking a component, and select Edit.

You can remove the resistive load, and substitute a 12V battery.

 

[Ajay Renganathan]

Thank you. It was helpful, but the one thing that I don't understand is how to select an IC. I understand buck converters but when going to an IC level I'm confused. Each IC has a different internal structure. In order to get an IC(by linear technology) for my voltage requirements how would I go about it?

 

[BradtheRad]

A safe charge current will be about C/10, or 200mA. There is a chance LT carries an all-in-one IC which contains the coil and all components.

LTspice is their free simulator. The menu contains a large number of their IC's. Including some for controlling switched-coil converters.

See their website:

https://www.linear.com

If you search this forum for the word 'buck', it should list several threads that discuss buck converters and IC's. Some IC numbers have been mentioned here several times. I have no direct experience with such IC's. Someone with experience might have a recommendation for you.