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  1. hevans1944

    Trouble understanding shunt resistance for short-circuit current measurement

    A good experimental procedure is what it is. A poor experimental procedure, performed for the sake of expediency or lower cost, isn't worth the paper the final report is printed on. Probably the point of interest in comparing the "efficiency" of solar cells is the maximum power point of a...
  2. hevans1944

    Trouble understanding shunt resistance for short-circuit current measurement

    Oh, yeah, no one has mentioned how you establish the "zero current" output state of the Allegro current sensor. The bipolar sensor nominally places zero current at one half the sensor supply voltage. The unipoloar version places zero current at one tenth the sensor supply voltage. Since neither...
  3. hevans1944

    Trouble understanding shunt resistance for short-circuit current measurement

    He is probably using the open-circuit voltage versus short-circuit current as a criterion for comparing solar cell efficiency among four test solar cells. And its a good excuse to bivouac in the desert.
  4. hevans1944

    Beginner assistance

    If you do decide to use wall warts, purchase two 12 V versions and use one to regulate +9 V and the other to regulate -9 V. Or just use them as-is for ±12 V supplies. Be sure the outputs are galvanically isolated from the power line. This is typical for wall warts that use switch-mode power...
  5. hevans1944

    Trouble understanding shunt resistance for short-circuit current measurement

    The resistance of 1,2 mΩ for the Allegro ACS711 has NO effect on its current measurement. It is only a consideration in limiting the true short-circuit current of the solar cell being tested. What accuracy do you require for the short-circuit current measurements? The Allegro measures, with a...
  6. hevans1944

    Dump load advice

    Have you investigated the compression carbon pile resistor? Might be hard to find one in the UK, but these were used as a variable load in a time long ago to test the current delivery (cranking ability) of lead-acid automobile batteries. Harbor Freight sells them. You could also build an R-2R...
  7. hevans1944

    Beginner assistance

    Good reply, Bob. On transistors: the MOST important thing to know is whether you are using a bi-polar transistor or "something else" like a MOSFET, SCR, TRIAC, FET, etc. Assuming you ARE using a bi-polar transistor (also called a BJT for Bi-polar Junction Transistor), the NEXT MOST important...
  8. hevans1944

    Trouble understanding shunt resistance for short-circuit current measurement

    Your approach seems very doable. But to obtain consistent results from day-to-day among a group of test cells you also need long-term accuracy, even when doing comparative measurements. Don't forget to record a date and time stamp along with data to identify specific solar cells in your SD...
  9. hevans1944

    555 pulse generator

    What value of resistance are you using for R2? How much stray capacitance is there from output to common? Can you post oscilloscope photos of the problem? What are you going to use the output pulses for? If you need pulses with 50% duty-cycle, it is better to run the 555 at twice the desired...
  10. hevans1944

    Vibrating Metronome Project

    I like Bob's electrical stimulus idea, but instead of a single pulse I would try a gated series of higher frequency pulses, perhaps a few thousand hertz gated on for a few milliseconds. Play around with the frequency, gate width, repetition rate and voltage to obtain a mild tingly sensation...
  11. hevans1944

    Need Help with Radio Shack Kit Project

    I think I bought similar parts kits a few years ago, mainly so I would have a box to keep them sorted... more or less. You can never have too many parts on hand; problem I have is finding them when I want to use them.
  12. hevans1944

    Trouble understanding shunt resistance for short-circuit current measurement

    The Hall-effect sensor is probably your simplest current-measuring solution, but you need to explicitly define what you are trying to DO. Take a look at the Allegro ACS723 for a sensor more closely matching your anticipated current range. The most precise current measuring techniques use a...
  13. hevans1944

    Special Project with led and motors

    It will rotate too fast. You may be able to excite it with a PWM (pulse-wideth modulated) power supply at a low duty-cycle to slow it down without losing too much torque or overheating the motor, but it really isn't the best choice for your project. You could also slow it down by using a large...
  14. hevans1944

    MMF

    And it's not really a force you are creating by passing current through a coil, it's an electromagnetic field. A force only occurs when something like a moving charged particle, another magnetic field, or the poles produced by the field interact with the field produced by the coil. A typical...
  15. hevans1944

    Special Project with led and motors

    Nice rose. How do you plan to mount the LEDs? I hope they will be external to the rose and the motor and you are not planning to rotate the LEDs with the rose. What is a "free rpm of 100 reduction gear motor"? Does the output shaft from the reduction gear rotate at 100 revolutions per minute...
  16. hevans1944

    2 Diodes in Series

    Are you seeking to posthumously win a Darwin Award with your project? Or perhaps, win one for a friend or family member?
  17. hevans1944

    Need Help with Radio Shack Kit Project

    I highly recommend the Radio Shack Learning Lab. Here is a link to the why. In a nutshell: excellent kit design, excellent instructions. I grew up reading Forrest Mims III articles, mainly in Popular Electronics. This man was (unknown to him, of course) my early mentor in electronics. There are...
  18. hevans1944

    Need Help with Radio Shack Kit Project

    There is one Radio Shack "learning kit" that I recommend, but this one isn't it. However, the purpose of this "lesson" is to teach you some of the properties associated with all relays: namely pull-in voltage and current, and drop-out voltage and current. There is a 9V battery and two...
  19. hevans1944

    Royer oscillator How it works ?

    You might want to visit this page for clues.
  20. hevans1944

    Mystery box

    Definitely contains some sort of DC power supply. From the front panel labels, it could be a gauss meter, used to measure magnetic field strength with a Hall-effect probe perhaps. Or maybe it is used to excite an external coil with who-knows-what method for detecting the resulting magnetic flux...
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