Rechargeable LED Lanterns

Replies

• 

  Abhishek Rawal

  A LED which gets its energy from USB & stores it in capacitor,so you can use it later.
  
  You'll need a LED(use multiple leds & resistors for lamp),a resistor,a capacitor & an USB.Connect 4th pin of USB to cathode of diode.Also Capacitor between 1 & 4th point of USB.And ofcourse a switch to open & close the circuit as required.
  
  Side note : You can create the circuit the way you want,The connection I mentioned is not mandatory but the components & the way they're connected surely play the role.
  
  Try drawing circuit & post the progress of your project here.
  Good luck 😀
• 

  lal

  But with a capacitor it wouldn't give any backup more than a second. There must be a battery too there.
  
  First thing would be to figure out how much light you need and then choose the right LED(s) for the purpose. Choose a battery that can provide enough power to keep the LEDs bright for your proposed time.
  Total time the battery lasts can be found out by (Ah rating of battery/current consumed by total circuit)
  Add a charging circuit according to the battery rating. It wouldn't be bad to have a solar panel charge the battery.
• 

  Abhishek Rawal

  lal

  But with a capacitor it wouldn't give any backup more than a second. There must be a battery too there.

  The backup depends upon the capacitor used.
  No need of battery if you're using Capacitor.Either use battery or capacitor. (if small number of LEDs you're using)
  
  But as you want "LED Lantern" which means around 25-30 LEDs then as #-Link-Snipped-# said battery is better option than capacitors.
  
  But if you're using battery then using USB will be dumb act.
• 

  Ramani Aswath

  
  
  Super capacitors have near infinite life compared to batteries.
• 

  lal

  Troll_So_Hard

  The backup depends upon the capacitor used.
  No need of battery if you're using Capacitor.Either use battery or capacitor. (if small number of LEDs you're using)
  
  But as you want "LED Lantern" which means around 25-30 LEDs then as #-Link-Snipped-# said battery is better option than capacitors.
  
  But if you're using battery then using USB will be dumb act.

  Let us do some math.
  Say there is a 1F capacitor and a 2V 10mA LED.
  So the LED needs 2 x 0.01 = 0.02W
  
  Assume the capacitor is charged to 5V initially(USB voltage). The LED can glow till the capacitor terminal voltage drops to 2V. Energy stored in a capacitor at a particular voltage is given by 1/2*C*V^2
  Total energy capacitor will deliver = 1/2*1F*(5*5 - 2*2) = 10.5J
  Total time LED will glow = 10.5/0.02 = 525 s = 8 minutes and 45 seconds
  
  That is when a 1F capacitor is used with a 10mA LED. One such LED won't be enough to be used as a lantern. And such a capacitor is too costly and pretty big.
• 

  Abhishek Rawal

  Oops my bad.
  I shouldve suggested battery & solar charging method(for sake of environment)
• 

  lal

  bioramani

  
  
  Super capacitors have near infinite life compared to batteries.

  Oh that is something new to me. Are Super capacitors cheap enough to be used in such applications?
• 

  Abhishek Rawal

  Now I am eager to do this practical & wanna see how long LED illuminates.
  Thanks for informartion #-Link-Snipped-#
  How can i forget basics ? Damn! my bad 😔
• 

  Jeffrey Arulraj

  Super caps are real cool But I am not sure about the availability in local markets We can get one for a price of 2 to 3 $ in the global market and shipping additional
  
  But if you try some manufacturers and purchase a good number you can get them at a real low price