NEWBIE NEEDS HELP! usb solar charger schematic double check

Discussion in 'The Projects Forum' started by Brian325, Oct 4, 2015.

  1. Brian325

    Thread Starter New Member

    Oct 3, 2015
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    hello guys im new to the forum i am working on a project solar usb charger i know that there have been simular post before . i have drawn up a very simple schematic i haven't wired anything yet. if someone could check it for me just to make sure i have no problems thanks Brian


    i have a few worries about my current schematic draft

    1 that the switches are wired correctly and that it is possible to get solar and voltage readings

    2 i wanted a way indicate that the solar cell was getting power so i am looking at getting a 9v pre wired led so i dont have to use resistors but if the solar cell is 9v and the led the same 9v will any power go to the rest of the circuit?

    i know i could use a regulator and resistors..but what would be the best way to go about having an indicator that the led is getting power

    i am using

    a car charger usb with 34063ap1 chip.. so the voltage will be relegated correctly (i think)?



    9V 3W Mini Solar Panel (cell)

    led indicator

    2 1N914 Schottky Diode

    9V Volt 300mAh Ni-MH Rechargeable Recharge Battery

    2 switches

    voltage meter
    Untitled.png




    i will attach schematic below
    thnaks again Brian
     
  2. Brian325

    Thread Starter New Member

    Oct 3, 2015
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    so ive done a little bit more research into leds and bow i know that pre wired leds already have resistors that can run from 12-9 volts
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,054
    There are a few problems. 1) The 3W output of your panel may not be enough to give acceptable charging. For instance I think an iPhone wants 1A at 5V, or 5W in order to charge up in a reasonable time. Your exact requirements will depend on the device you are charging. 2) You haven't shown any voltage regulator. Anything that plugs into a USB port expects to find a regulated 5.0V there. It's possible that 9V from your panel could damage a sensitive device. 3) Your diodes are backwards in the drawing. The stripe on a diode points in the direction of conventional current flow, towards the lower voltage. 4) You only need a diode to prevent reverse current to the panel when it's dark. The second diode on the right serves no purpose, but that's where your regulator needs to go. 5) You probably don't need to switch your voltmeter from the battery to the panel. When the panel is lit, it will be ~0.7V higher voltage than the battery. (The difference being the ∆V across the blocking diode.) When the panel is not lit, the voltage will fall below the battery, but who cares? 6) Your diagram shows the switch as being shunted across, unable to do its job.
     
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  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Is 9 V solar panel open circuit V or nominal operating V? 9 V OC under load about = about 6.75 V. If 9 V is rated operating V , then OC about 12V. 9 V output + diode will not charge a 9 V battery. Looks like chip is a DC-DC switching regulator chip.
    If solar panel had enough V to charge battery, then at 3W would be more than 300mAh battery could take.
    Suggestion: Start over.
     
  5. Brian325

    Thread Starter New Member

    Oct 3, 2015
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  6. wayneh

    Expert

    Sep 9, 2010
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    One approach to "proper parts" would be look over the commercial solutions already available You might decide one of them suits your needs.

    If you insist on re-inventing the wheel for yourself, you could look into DC-DC converters. Many are available on e-bay for instance, and many have USB output. They might even have the blocking diode built in, giving you a one-module solution.

    Investigate what the iPhone requires on the USB data pins in order to initiate charging. Just having power is usually not enough.
     
  7. Brian325

    Thread Starter New Member

    Oct 3, 2015
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    unfortunately i have already bought the 9v 3w solar panel.. if i change the batter's to 5AA's the solar panel should change them with out any problem correct. if one battery is 1.2v then 5 batteries would be 6volts. sorry about the double post my bad
     
  8. Brian325

    Thread Starter New Member

    Oct 3, 2015
    9
    0
    i will look into it thanks for the heads up
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Measure the open circuit V of the solar panel so that we know what we are working with.
    5 Ni-MH cells will need at least 7.5 V for charging & needs over V & under V control.
    Specs. on 1N914 sais that is a bad shottky, Vf .7 to 1V or just a plain 1N914 @ maybe US $ .10.
    Use at least a 1 A diode, say 1N4001.
     
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