solarpoweredlightcircuit

Discussion in 'General Electronics Chat' started by scopesys, Nov 26, 2012.

  1. scopesys

    Thread Starter New Member

    Nov 23, 2012
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    Hey guys, this is my first ever post on this forum and I'm a complete newbie when it comes to electronics, I have not done any classes what so ever regarding electronics (other than some short classes in physics during highschool), just ALOT of reading so everything I already know has been self taught.

    I just bought something however because i was simply fascinated by it for a few reasons:
    1) It uses 3 white LEDS
    2) White LEDs have a forward voltage of approx 3volts each?
    3) Yet it runs on a 1.2V AA battery

    Now I know current can be stepped up however thats AC, what fascinated me about this device is its stepping up DC voltage from 1.2 to 3.x volts and i simply want to know how it does it.

    These are the images of the circuit board, if you can make out how it does it, can you please explain how its buffing this specific circuit is buffing voltage? If possible I'd like to thoroughly understand it as I might use such a circuit when I start making my own stuff (such as why there is two resistors there in parallel?)

    I also have one more 'side' question out of sheer curiousity:
    I obtained a second one of these devices, and hooked them in series to two batteries in parallel
    IE:
    --Solarpanel--Solarpanel--
    ---------1.2V Battery-----------
    ---------1.2V Battery-----------

    Now to turn the panels lights on either one, I have to switch them BOTH on and I dont get that since I've been under the assumption that theres always a connection either between the lights-battery OR solarpanel-battery.. So why cant I turn them on individually?


    Anyway, I want to modify the original so that it turns on in the dark automatically by adding a photoresistor so partly I need to know if the device is STILL CHARGING while switched on

    Later on im planning on mounting this thing on a spindle and want to it to rotate automatically with the sun (need to know hot to inverse the function of a photoresistor I guess but thats another topic :p)

    Thanks guys (oh and, sorry to the peeps with slow internet, I just read that you guys don't like opening outside links though :p)

    BTW I've been scratching my head on why I cant post on this forum and I just figured out my title can only be one word to post.. so hope that explains the lack of spaces there xD.. whats up with that?


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  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Solar night lights can light a 3V LED off a 1.2V battery since they have a DC-DC boost converter built into them. That's why there is one or more inductors (L1 is such) on that board. Hard to tell from the pictures but those two "resistors" in parallel may also be inductors.

    Here's a discussion of some units I tore down.

    To fully understand your device you would have to carefully trace out each and every part and connection to make your own schematic. I can start you off by telling you the 3 LEDs are in parallel, and D1 connects the solar panel to the battery and blocks the battery from discharging thru the solar panel at night.

    I would have no idea why you see what you see when you try to connect 2 units.

    Next time make your images smaller so they fit on the page. Right now they are about 2 screens wide which makes your post nearly unreadable. I had to copy your text to notepad to be able to read it without getting seasick from constantly sliding the window all over.

    Post titles are limited to some 25 characters. More then that and it gets weird, but less then that and you can use separate words.

    And welcome to the forums.
     
  3. scopesys

    Thread Starter New Member

    Nov 23, 2012
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    0
    yea sorry about the images >_<... i realized they were too big only when I posted them lol

    Anyway thanks for that link, was able to learn a few new things however it has raised ALOT of questions and if you dont mind answering any amount of them I would really appreciate it :)==>

    Ok so that first part of your circuit has a diode which as you explained is to prevent the battery feeding energy into the solarpanel when its not in the sun..
    Now the second part(L1,L2,C1), why 2 inductors and not 1? and whats with the capacitor? Is it there to provide a discharge into the photoresistor?

    The third part (R1, Q1 and the photoresistor(CDS)) Im VERY interested in since that was going to be my next question lol.
    I see the function of this device is exactly like the one in my post except with the added CDS to light in the dark, now I understand CDS resistance decreases as light increases, my question is how do you get the opposite effect which you've obviously done.

    Heres how im interpretting it, can you please correct my interpretation: The capacitor is discharging its current into resistor 1 and from there it can either go to the transistor or into the CDS depending which has the lower resistance. If light is shone onto the CDS, the resistance is low and it flows through there, if there is no light, the transistor has the lower resistance and the current therefore goes to the base of the transistor and comes out the emitter.

    My final question is, what happens after the current passes through the transistor? Is it any different to when it passes through the CDS? the only way it can go in EITHER case according to my interpretation is back to the battery providing a voltage boost, so why does passing through the transistor provide this voltage boost while passing through the CDS does not?
    I've obviously interpreted it wrong just not sure how so :/...


    Thank you VERY much
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    There is no part 2 and part 3. Everything except the solar cell and D1 make an oscillator. It runs as described in the other post.

    The CDS resistance does indeed decrease with increasing light. So as it is used here it keeps Q1 off when the sun is out by shorting the base to emitter (no base current means Q1 is off).

    This circuit can increase the voltage thus: Just look at the B1-L1-Q1-LED loop. When Q1 is on it causes a current to (quickly) build up in L1. Then when Q1 turns off this current must transfer to somewhere and thus it goes to the LED. As L1 is a current source the LED controls it's own forward voltage to exactly what it wants to use that current.

    Pressing the "Go Advanced" button below the post window brings up a "Preview Post" button. This allows you to catch things like huge images before you commit them. When your post count goes up you can edit your own posts too.
     
  5. scopesys

    Thread Starter New Member

    Nov 23, 2012
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    Ok i got most of that except slight confusion here:
    1) Why can't a charge build up anyway without the transistor by passing through the L1,L2,C1 loop? Is it due to the capacitor?
    2) Why would Q1 turn off? Shouldn't it be turned on for the duration of the night, and hence a current pass through the LED for the time that its on and not off?
    3) In the last sentence, are you saying that the forward voltage on the LED changes?

    Once again,
    Thanks :)
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Did you read the other post I linked? It says this circuit oscillates at 310 KHz, and each and every cycle the transistor turns on and off.

    There may just be a few parts in this circuit but it is quite complicated in it's operation. It is acting like an oscillator and a switching power supply and a battery charger and a dark detector all at the same time. It's not the type of circuit you want to learn electronics with.

    Wiki "boost regulator" to see how just one part of this circuit works.
     
  7. bug13

    Well-Known Member

    Feb 13, 2012
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  8. scopesys

    Thread Starter New Member

    Nov 23, 2012
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    Lol yea I came here not knowing muchat all about an inductor, knowing that, the circuit is alot clearer, Whats left to learn I guess is how to create a rapidly oscillating circuit just like Ernie's circuit which I'll have to read about tomorrow (currently 12am, better to not have to read the same thing 5 times to finally get it xD).