Solar Engine

Discussion in 'General Electronics Chat' started by daroc26, Apr 4, 2009.

  1. daroc26

    Thread Starter Active Member

    Apr 4, 2009
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    Hi All,

    I'm a transplant from the electronics-lab forum. I lurked there for a year, asked a question and got no response.

    I've been lurking here for a little bit and noticed that it's a little more active.

    I'm an electronics newb. I've been checking out every site on the web, every book, and makezine blog, trying to learn about electronics. I get a little obsessed at times, thinking about the next great idea. I have a breadboard, I've ripped some components out of old electronics, and now I want to build.

    I'm really into the BEAM movement and using solar cells. I just love that technology. But I don't understand the solar engine. What is the benefit of the solar engine, as opposed to hooking the solar cell to a capacitor and then to a motor or other load? I think it's because the transistor acts a switch which allows the circuit to build up more voltage before releasing to the motor. If this is right, doesn't the cap do the same thing?

    Any help would be much appreciated!

    Thanks
    Daroc
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    BEAM movement? Not familar with it.

    A cap will handle surges, while a solar cell has a low but steady output. The two work together pretty well.
     
  3. daroc26

    Thread Starter Active Member

    Apr 4, 2009
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    Hi Bill, BEAM is the creation of Mark Tilden...Autonomous robots that mimic biological beings in nature...it's pretty cool. Just google BEAM and I think you'll be inspired.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    BEAM has a big emphasis on small and recycling tech junk, and being solar powered. There is a huge emphasis on simplicity (with a certain definition of simplicity, i.e. no uC).

    The "brains" are inverters set up as ring oscillators, typically one for each side of the robot. Sensors on each side will alter the frequency of the oscillator, causing the robot to turn towards the stimulus.

    Adding more oscillators and more sensors can create centipedes and other forms.

    Making them work is three quarters mechanical, with the electrical part being soldering components to several inverters in parallel for oscillation and enough output power to drive small motors. They are typically built to mimic nature, by doing somewhat 'advanced' processes without a microcontroller. All of the ones I've seen are built "dead bug freeform" style, no pc board, with lots of hot glue and epoxy.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Googling "solar engine" brings up a number of entities like a radiometer and a Stirling-cycle motor. When you refer to "the" solar engine, it does not identify anything. Can you be more specific?
     
  6. daroc26

    Thread Starter Active Member

    Apr 4, 2009
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    Hi beenthere, sorry, try googling BEAM Solar Engine.

    http://www.solarbotics.net/library/circuits/se.html

    This is the listing of the Solar Engines. I'm struggling to understand Type 1, 1381 SE, FLED, Miller SE.

    The site has all of the schematics and details.
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    [​IMG]

    Solar Engines charge a cap with the solar cell, once it it is 'full', it dumps the charge through the motor for movement.

    This allows the use of solar powered items when there isn't much light, though only in pulses.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Okay. Almost looks like you could do the same thing using a 2N2646 UJT.
     
  9. daroc26

    Thread Starter Active Member

    Apr 4, 2009
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    I guess my question is whether I need to use the transistors, 3904 etc.? What do you believe would be the difference in the circuit?

    Thanks!
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    With a good/large cell in bright sunlight, with a small motor, the motor would turn. In not-so-good light, the motor's low resistance would use all the power as it was generated by the cell, without turning, as the voltage/current is too low.

    The transistor is acting as a swtich. It keeps the motor disconnected until a certain voltage is reached (1381 does does that), once there, a charge is put to the base of the transistor, turning it on, which dumps the rest of the motor charge through both the transistor and motor.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    So what are you using the intermittent motor for?
     
  12. thatoneguy

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    Feb 19, 2009
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  13. daroc26

    Thread Starter Active Member

    Apr 4, 2009
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    Wow, Thanks so much for the help. This not only helped me understand this circuit, but I also learned a little more about reading schematics.

    Bill, right now I just want to learn the fundamentals. If I can get a motor to turn, an LED to light, and a piezo to buzz, I'll be 100% satisfied. But eventually, I'd like to do something more complex with solar energy.

    I appreciate everyone's assistance! I'm sure I'll be back at some point!
     
  14. daroc26

    Thread Starter Active Member

    Apr 4, 2009
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    Hi All,

    I'm back to follow up on this topic, the BEAM Solar Engine. I am trying to breadboard the FLED Solar Engine as documented here:

    http://www.solarbotics.net/library/circuits/se_t1_fled.html

    I was unable to obtain a 4700uf Cap due to the cost at Radio Shack (over $4.50 for one!) so I am using three 1000uf Caps. Two (6.3v) were scavenged from a telephone circuit board, the larger 35v cap was purchased at RS.

    The Solar Cell was scavenged from a Solar-Powered Calculator. I have sourced the datasheet and attached it.

    From what I understand, the FLED should trigger when the voltage reaches 2.4v.

    According to my meter, the cap is charging to 2.3v. Why can't it reach 2.4v???

    Looking at my breadboard, the orange and yellow wires are the output to a small motor. I am hoping the circuit would trigger and then turn the motor in small increments.

    If anyone has any ideas to make this work, please let me know!

    Thank you!
     
  15. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Hi,
    I think the increased leakage currents as the circuit gets near the turn-on threshold are preventing the voltage rising any further.

    If you go back to the solarbotics page in your last post, there is a modified version further down where the FLED is coupled by a resistor and capacitor, rather than being directly on the transistor base. (The circuit is also doubled, ignore the duplicate).

    The idea of that is that the FLED does not draw any current through the transistor until it 'fires', at which point the capacitor feeds a pulse to the transistor base, turning it on.

    Both circuits have a serious problem to me - the collector of the first transistor is connected directly to the base of the second transistor.

    Remembering that the base-emitter junction is effectively a diode, when the first transistor turns on the capacitor is being shorted out through the second transistor base, losing much of the stored energy.

    Adding a low value resistor in that collector to base connection would significantly increase the overall circuit effectiveness. The best value is a matter of trial an error, but something in the ten ohm to one hundred ohm range should work.
     
  16. BMorse

    Senior Member

    Sep 26, 2009
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    The transistor is there to take the load of the motor when on, the 1381 would not be able to handle the current draw of the motor... so in essence, it is just a switch, you can get different voltage level triggers (1381's) to turn on the 3904 at different voltage levels.... Since most of these "Solar engines" are used in photopoppers, they need to build up the amount of power stored in the caps, and then it is let out all at once to activate the motors, hence the little popping action of the BEAM Photopopper.... The best ones that I like are the 1381 based ones.....
     
  17. BMorse

    Senior Member

    Sep 26, 2009
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    What is the output of your solar panel without a load? and what is the output with the Load connected? Most FLEDS or Solar engines need a solar cell that puts out at least 3.4 to 5 volts in direct sunlight.....
     
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