solar LED lightwith rechargeable battery and a mini solar panel

Discussion in 'The Projects Forum' started by rkrao, Sep 17, 2016.

  1. rkrao

    Thread Starter New Member

    Jun 30, 2011
    I am a retired forester interested in electronics as a purposeful hobby;presently trying to build a very low-cost solar LED lamp;there are several such lamps in the Indian market targeted at the middle-class customer and not the poor / tribal communities;secondly these lamps provide a mini solar panel and the LED with a life of perhaps 20 years and a battery that lasts for less than three years and no provision for replacement of battery !the purchaser has to throw this light or give to his children as a toy once the battery is dead;i am trying to make a light with a provision for a replaceable rechargeable battery;I have identified a low-cost[Rs.20] Lead-acid rechargeable 4 volt ,500mA battery to power 4nos pirhan LEDS [20mA] and i propose to charge the battery with a mobile phone charger where power is available and with a solar panel where power is not available;it is a not for profit venture;i welcome suggestions from the August members of this website.I served in tribal areas for twenty years .Thanking All.
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Welcome to AAC!
    Don't you have cheap solar-powered garden lights available where you live? It will probably cost more to build a light than to buy one.
    No self-respecting hobbyist would allow that to happen :D. Open up the light, get the wire-cutters and soldering-iron out and stick a new battery in there! At the very least you could re-use some of the parts of a cheap light.
  3. rkrao

    Thread Starter New Member

    Jun 30, 2011
    These lights have some chinese batteries of unknown voltage and non-standard size unavailable in the market+lights are in widely dispersed rural /forest areas ! I want to build new lights that are simple to operate,last for two or three years and replaceable batteries that are locally available.
    Regarding the other suggestion of using a garden light,they are not available nor a solution. !
    Can readers suggest a circuit that can light up 3/4 20 mA white LEDS with preferably one rechargeable battery to be recharged by a mini solar panel !
  4. drc_567

    New Member

    Aug 23, 2016
  5. BR-549

    Well-Known Member

    Sep 22, 2013
    Could we see a couple of pictures of the unit? One of the complete unit and one of the insides with the battery.
  6. drc_567

    New Member

    Aug 23, 2016
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
    My piranha white LEDs are rated 3.2 Vf.,@ 30 mA. 25k mCd.
    4 LEDs = 120 mA X 10 h = 1.2 Ah X 2, for unpredictables, = 2.4 Ah.
    3 AA NiMH 3.6 V, a little tight so 4 NiMH, AA = 5V allowing a bit of head room @ 2650 mAh.,per Duracell.
    Charge to 6 V needs SP to produce 9 to 12 V OC. 2600 mAh/ 8 hr. = 325 mA. SP about 6 X 10 in.
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
    Like this?
    and this?
  9. rkrao

    Thread Starter New Member

    Jun 30, 2011

    Thanks for the response from several experts;i am giving more details and some photographs .The inputs i need are-1.the specifications for a mini solar panel to fit on to the box cover of 9x5cm.;2.the diode to protect the battery from reverse charging;3.the DC-DC boost if i have to use a 1.5v rechargeable AA battery and its circuit diagram; 4.does this simple circuit need a PCB and is there an alternative approach.
    You may please click the above link to see more details.
  10. Xerox

    New Member

    Aug 6, 2015
    Hello rkrao

    Most of these LED lights are designed as novelty throw away items and use as you say non standard components. The real issue as I see it is one of robust reliability. Some suggestions for your high level design specification:

    1. Use Lithium Polymer technolgy instead of NiMH. A battery charge chip would be required.
    2. Use a back connected solar cell they have efficiencies of around 20%.
    3. Use a constant current source circuit to power the LED. Avoids wasted energy.
    4. Use a boost regulator to power your circuit from the battery.
    5. Insect and humidity protect your circuit board by conformal coating.

    Economies of scale kick in if the market is there. See if you can get somebody in Hong Kong to design and make some of these for you to test. The middle classes (anna wise rupee foolish) are alway prepared to spend a little extra to buy reliable quality.
  11. burger2227


    Feb 3, 2014
    Make your own out of solar lights or a 5252 F chip with pre-made coil and one to three 1.2 v rechargeable AA batteries..

    The 5252 F chip doubles the voltage, turns off the LED when solar cell charges during day and shuts down to prevent
    over discharge of the NiMH battery. below .9 volts.
    Last edited: Sep 23, 2016
  12. ian field

    Distinguished Member

    Oct 27, 2012
    Sometimes I do it the other way round - I wanted some colour changing LEDs for PC power LEDs, so I bought a few colour changing garden lights from the £ store.

    They'd have been cheaper from Farnell, but I couldn't think of enough stuff to make up the minimum order charge.
  13. rkrao

    Thread Starter New Member

    Jun 30, 2011
    Thanks a million to XEROX,Burger2227,and distinguished member Ian field for their suggestions.Searching the web i came across a very simple circuit by an young electrical engineer ,Debasish Dutta in 'instructables' using IC QX5251F[similar to the QX5252 suggested by Burger2227];;you can see his presentation in you tube at-
    . and in his website'open green energy'.on my request he has sent me one PCB with the components all soldered on to it yesterday.;with very few components and hardly one sq.inch in size,it is a very simple and elegant piece of art ,i should say.But cost-wise it exceeds my expectations;the rechargeable AAA nimh battery costs one US$ and the solar panel another two dollars even in Alibaba website!I The battery is a must but i can [if it is possible]do without the solar panel and substitute power supply with a mobile phone charger;now the mobile phone is ubiquitous even in remote tribal communities and can be used to charge the pocket LED.I am asking Debasish and my request to you all is to suggest a modification to the circuit forrecharging the AAA 800mA battery with a mobile charger.My objective is to produce a pocket LED light which poor students can use for reading their books at a quiet corner at an affordable price of not more than INR 100[US$1.5]and the eneloop battery to last for five years !Thanking you all once again.rkrao