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  1. duke37

    I can't see how this will work

    The 1k resistor allows positive feedback. This makes the circuit have hysteresis. You could drop this to say 100Ω or use a 1k variable resistor to set the hysteresis. It would be simpler to use a comparator where the hysteresis could be calculated.
  2. duke37

    Popper Pot specs?

    You will need a very big rheostat to handle 1440W (12A). I would go for a simmerstat as used on a cooker. This will turn on and off but the time constant may be short enough to generate a fairly constant temperature. Half power can be obtained by putting a diode in the supply. The fan motor...
  3. duke37

    I can't see how this will work

    That does not make sense. Have you got the LED connected the right way round?
  4. duke37

    I can't see how this will work

    The 100k resistor is not simple resistor, it is a potentiometer with a twiddle adjustment.
  5. duke37

    Light Bulb

    I would use a wall wart with AC output. Rectify this to give a power supply for the circuit with a suitable time constant. Compare this supply with a reference and drive a relay. You will only be dealing with low voltage in the circuit so safe for a beginner.
  6. duke37

    Capacitor help

    I see two transformers. These will produce sound waves by magnetostriction.
  7. duke37

    IDENTIFY Transistor from its Hfe Value

    Speed may also be important. Switching at a few kHz should be no problem. Switching at 1MHz may be. Also, power dissipation. Can you describe what the circuit does and if possible show a diagram?
  8. duke37

    Transistor as a switch

    This would be the case if all transistors were passing an appreciable current. Take the case of three transistors with the final transistor passing 100mA. Its base current will be 100mA/gain, say 100/200mA = 500µA. The next transistor will need a base current of 500/200µA=2.5µA The first...
  9. duke37

    Why Low output voltage for wind turbine?

    If you are stuffing 18A into a 12V battery and only getting 10V, then you have a shorted cell.
  10. duke37

    picking components for a stir plate

    An ordinary potentiometer such as you show is just not man enough for the job. That is why car heaters use a switch and bigger resistors. If you wish to stick with a potentiometer, then you will have to follow it with an amplifier. This can be as simple as a power transistor mounted on a heat...
  11. duke37

    picking components for a stir plate

    Go down to your local scrap yard and get a switch and resistors which control a vehicle heater fan. With luck, you will get a choice of speeds which will suit.
  12. duke37

    Why Low output voltage for wind turbine?

    I agree with davenn and Kiwi. AC induction motors have no way of generating a magnetic field on their own. They can sometimes be encouraged by loading with capacitors but a complex control system is needed. DC is needed so use a DC generator.
  13. duke37

    Transistor as a switch

    1. The first thing to consider is the voltage divider made from R1 and the LDR. Any load on this will affect the output voltage. We have not got anywhere near the relay yet. To get this divider to work properly an amplifier is needed which takes negligible base current. 2. I did not get what...
  14. duke37

    Rectifier Help Needed

    Present day vehicle alternators are built with considerable leakage inductance which means that the current is limited and they will not burn out if shorted. The impedance of the inductance is proportional to frequency as is the generated voltage. These two cancel to give a current limit which...
  15. duke37

    Rectifier Help Needed

    It would help if you would give more information on the alternator. Is it on a motor bike or car or is it in a power station to provide electricity for a town? How about a picture? Variable speed alternators are designed differently from fixed speed alternators but have similar circuitry. As...
  16. duke37

    Transistor as a switch

    I cannot replace Kris but will try to help a little. 1. If the voltage divider is unloaded, then the current through R1 will be the same as the current through the LDR. Hence the equation. 2. The 0.7V which is used is a rough estimate of the base/emitter voltage. I have not deduced what your...
  17. duke37

    Wattmeter with analog output

    This is not easy, power is Volts * amps * power factor The volts and amps are easy, the power factor is not.
  18. duke37

    Fender stage 160 amp blowing fuses

    I have not played with guitar amps but here are some tips. The use of a lamp limiter is good. The 300W bulb should not light up when the amp is not giving output as the quiescent current should be low. 100W bulb should be plenty. We do not know what the red wires do. If there is a loud hum...
  19. duke37

    Minimalist 2 cell Li-ion Battery charger

    With 3.7V out and a 3.6V zener, you will be left with 0.1V to charge battery 2. This will not work. Are you going to connect the batteries in parallel for use? What will be the effect if they are not exactly equal. You would be better to use and charge the batteries separately.
  20. duke37

    Resistance of double sided adhesive conductive carbon tape

    I think the measurement should be made from one edge to the opposite edge. Using a small diameter probe would give too high a resistance reading. That looks like a good square meal.:)
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