Solar Pocket LED Light

The post explains a simple low cost solar pocket LED light circuit which could be used by the needy and, underprivileged section of the society for illuminating their houses at night cheaply.

The idea was requested by Mr. R.K. Rao

Solar Powered LED Table Lamp


I want to make a SOLAR pocket LED light using a 9cm x 5cm x 3cm transparent plastic box [available in the market for Rs.3/-] using a one watt LED/20mA LEDS powered by a 4v 1A rechargeable sealed lead-acid battery [SUNCA/VICTARI] & also with a provision for charging with a cell phone charger [where grid current is available].

The battery should be replaceable when dead after use for 2/3 years/prescribed life by the rural/tribal user.

This is meant for use by tribal/rural children to light up a book; there are better led lights in the market for around Rs.500 [d.light],for Rs.200 [Thrive].

These lights are good except that they have a mini solar panel and a bright LED with a life of ten years if not more ,but with a rechargeable battery without a provision for its replacement when dead after two or three years of use.It is a waste of resource and unethical.

The project i am envisaging is one in which the battery can be replaced , be locally available at low cost. The price of the light should not exceed Rs.100/150.

It will be marketed on not for profit basis through NGOs in tribal areas and ultimately supply kits to tribal/rural youth to make them in the village.

I along with a colleague have made some lights with 7V EW high power batteries and 2x20mA pirahna Leds and tested them-they lasted for over 30 hours of continuous lighting adequate to light up a book from half-meter distance; and another with a 4v sunce battery and 1watt 350A LED giving enough light for cooking in a hut.

Can you suggest a circuit with a one AA/AAA rechargeable battery,mini solar panel to fit on the box cover of 9x5cm and a DC-DC booster and 20mA leds. If you want me to come over to your place for discussions i can.

You can see the lights we have made in google photos at https://goo.gl/photos/QyYU1v5Kaag8T1WWA Thanking you,

R.K. RAO

The Design


As per the request the solar pocket LED light circuits needs to be compact, work with a single 1.5AAA cell using a DC-DC converter and equipped with a self regulating solar charger circuit.

The circuit diagram shown below probably satisfies all the above specifications and yet stays within the affordable limit.

Circuit Diagram


solar pocket LED light circuit

The design is a basic joule thief circuit using a single penlight cell, a BJT and an inductor for powering any standard 3.3V LED.

In the design a 1 watt LeD is shown although a smaller 30mA high bright LED could be used.

The solar LED circuit is capable squeezing out the last drop of "joule" or the charge from the cell and hence the name joule thief, which also implies that the LED would keep illuminated until there's virtually nothing left inside the cell. However the cell here being a rechargeable type is not recommended to be discharged below 1V.

The 1.5V battery charger in the design is built using another low power BJT configured in its emitter follower configuration, which allows it to produce an emitter voltage output that's exactly equal to the potential at its base, set by the 1K preset. This must be precisely set such that the emitter produces not more than 1.8V with a DC input of above 3V.

The DC input source is a solar panel which may be capable of producing an excess of 3V during optimal sunlight, and allow the charger to charge the battery with a maximum of 1.8V output.

Once this level is reached the emitter follower simply inhibits any further charging of the cell thus preventing any possibility of an over charge.

The inductor for the pocket solar LED light circuit consists of a small ferrite ring transformer having 20:20 turns which could be appropriately altered and optimized for enabling the most favorable voltage for the connected LED which may last even until the voltage has fallen below 1.2V.

Need Help? Please send your queries through Comments for quick replies!




Comments

krishna rao said…
Thanks a million for the circuit design;it will take sometime for me to understand it;the TR1 ferrite ring transformer has to be made or will it be available in the market.Alternately is there any thing that can be substituted in its place.I came across a long time back,a made in Germany LED driver that boosts the DC current from 1.2v to 3-3.5 volts,but could not find it in the Indian market online.Can you suggest something like that.with warmest regards.rkrao
Swagatam said…
You are welcome!

TR1 has to be made by hand, and it's very easy, you can refer to the video in the following article to get an idea regarding the coil.

https://homemade-circuits.com/2012/10/1-watt-led-driver-using-joule-thief.html

The concept that you are referring to could have also used the same principle as above because it's the most effective way of transforming 1.5V to 3V and higher.
Olayinka said…
Thanks for your contribution so far, please is there any ways to make DYA (local made) solar cell
manjunath said…
Sir was this ferrite rod mean. was that rod situated in middle of an dry battery. Or different
Swagatam said…
yes it's possible, you can search it online for the details...
krishna rao said…
thanks for the response;i will try it.with warm regards,rkrao
Swagatam said…
Manjunath, battery central rod is a graphite rod, not ferrite

ferrite rod can be found inside old MW radios.
Sharoj Al Hasan said…
Sir please help me i want to make a circuit which will on the relay for 2 hour then Off the relay for 2 hour ... it will continue automatically when switch on
Swagatam said…
Sharoj, you can use any IC 4060 timer circuit for it...
Sharoj Al Hasan said…
Sir can you please give me the circuit diagram
fayyaz said…
sir i need automatic led torch circuit .using TP4056 li-ion battery module.
Swagatam said…
fayyaz, please provide more details about your requirement, in the meantime you can also check out this article

https://homemade-circuits.com/2017/04/li-ion-battery-charger-circuit-using-ic.html
Aabhishek Sharma said…
Hi sir,
If i'm having a 6v 2.4w solar panel can i amplify its output voltage and current ,can lm338 help me.
Swag said…
You can modify current or voltage but the output will be always less than 2.4 watt, that is the output V x I product will be less than the input V x I. LM338 cannot be used for this, you will have to use a buck converter or a boost converter
Vishwa mukh said…
Sir,
The simple solar battery charge controller is working very well. It am delighted that I could make and use it with your prompt help. I will try to build solar pocket LED light circuit.

Can you please provide me links to basic electronic circuits. I want to use the solar breadboard to make basic electronic circuits to learn and understand basic electronics
Thanking you for your time,
Swag said…
Hi Vishwa, I ma glad it is working for you.

You can try the following link, you will find many small transistor based circuits here

https://homemade-circuits.com/?s=transistor+circuits
Vishwa mukh said…
Sir,

Thanks for your prompt reply.

Thanking you for your time,
Vishwa Mukh Bharadwaj said…
Sir,

The simple solar battery charger circuit is working very well. I want to modify the above circuit so that the battery does not discharge below 1V. Where can I fit the LDR so that when the system is put in the sunlight, it switches off the LED light and starts charging the cell and during night it starts discharging.
Thanking you for your time,
Swag said…
Vishwa, you can try the last design from this article

https://homemade-circuits.com/simplest-automatic-led-solar-light/
Vishwa mukh said…
Sir,

Thanks for your prompt reply, this is what I needed.
Thanking you for your time,
Swag said…
you are welcome!!
Vishwa Mukh Bharadwaj said…
Sir,
I have a 5V rechargeable battery. wh I use it to light a night lamp. During the day it is recharged with a solar panel. During night it discharges to 3V. Please help me to understand, if an increase in voltage causes increase in current or increase in current causes rise in voltage?
Thanks,
Swag said…
Vishwa, an increase in voltage will drive more current into the load if the source has sufficient current, so yes rise in voltage will increase current drive...but rise in current will not necessarily increase voltage.
Vishwa Mukh Bharadwaj said…
Sir,
Thanks a lot for your prompt reply.
Regards,
Vishwa Mukh Bharadwaj
Swag said…
You are welcome Vishwa!

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