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  1. duke37

    Help With Kids Homework

    I agree with Gryd3 'Ferrite' can have different meanings. It is the low temperature body centred cubic magnetic phase of iron. This is used in transformer cores and is split into laminations to increase resistance and reduce eddy currents. It is also alloyed with 4% silicon to increase...
  2. duke37

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    The two weights are operating in opposition, when one is falling, the other is rising so the nett restoring force is smaller and the frequency will be less. Or am I wrong? If the weights are the same and the pendulum is pivoted in the middle, there will be no restoring force and the frequency...
  3. duke37

    electrolytic capacitor polarity help

    This looks to me to be a mutivibrator (oscillator). Collector to base, collector to base. The emitter/base junction of the PNP transistor acts as a rectifier to get the polarity right.
  4. duke37

    looking for a "center-bore" motor

    These bearings are probably deep groove ball bearings so they can take some axial load as well as radial load. They will probably have a enough clearance to make them floppy. Thus to get a shaft without wobble you need two bearings. Cars and washing machines use preloaded bearings to take out...
  5. duke37

    voltmeter on bridge rectifier

    Without a capacitor, the meter will read the average voltage which is Vrms*0.9 With a capacitor the meter will read the peak voltage, Vrms*sqrt(2).
  6. duke37

    Frequency for Beginners

    "So I imagine the antenna determines the radius of the electromagnetic field," Take a bucket, half fill it with water to make it heavier then pump it up and down in a pond. You will see ripples diverging from the bucket. The wavelength is the distance between the ripples and will be smaller...
  7. duke37

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    @hevans1944 I do not believe than dropping the Q of this circuit will affect the frequency significantly. Of course much more drive power would be required. A swinging weight above the pivot point has been tried. I am surprised that this made no difference to the frequency. It is 60 years...
  8. duke37

    How to calculate run time of inverter

    Can you do some sums? The last sum I did can be modified for the numbers you have.
  9. duke37

    How to calculate run time of inverter

    2.5A at 120V = 300W output 300 / 0.92 = 326W input to the inverter. 326 / 24V = 13.6A battery current 200 / 13.6 = 14.7h to discharge the batteries completely (not a good thing). 200Ah at 20A = 10hr.
  10. duke37

    12v lighting system

    LEDs will give more lumens per watt.
  11. duke37

    looking for a "center-bore" motor

    I would go for the belt solution. You will need to decide the size of the tube and the torque required. If you decide on a tube of 25mm OD then the bearings will be quite large to hold it. Two bearings in plummer blocks spaced 100mm will give stability. If the torque is low, a flat belt will do...
  12. duke37

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    You could use a minature electric motor and gearbox to crank the pendulum forwards and backwards. It would use much more power than needed to maintain a pendulum at its natural frequency.
  13. duke37

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    The period of a pendulum is 2*pi*sqrt(L/g), weight does not come into it other than moving the center of mass thus affecting the effective length (L) To halve the frequency, you will need to make the pendulum four times as long. It is no coincidence that all long case clocks have the same...
  14. duke37

    looking for a "center-bore" motor

    You may be better off to separate the motor from the hollow shaft. Then you could use a small high speed motor and drive the shaft with a belt.
  15. duke37

    Variable Capacitor Capacitance

    If you post a picture, someone may be able to hazzard a guess. Include a ruler.
  16. duke37

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    You may be able to devise some kind of pendulum suspension which gives an apparent higher pivot point. This type of thing is used in vehicles so that they tip over less on corners. You need to find a tame engineer:).
  17. duke37

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    I see no pendulum. A pendulum frequency is set by the length and the gravity field. To make it run slower, you can make it longer or move it to the moon. The pictures you show appear to be a battery supplied impulse generator to maintain the pendulum, replacing the energy lost in friction...
  18. duke37

    Help identifying this component {Diode}?

    What is the supply voltage. The rust would indicate that it might have been used outside and be battery driven, then the input voltages would be low. It should be possible to sketch out the schematic with such a simple circuit.
  19. duke37

    Help getting my circuit to work - sound card osciloscope calibrator

    There is no multivibrator in your circuit. TR1 can only pass less than 10mA because of R4 and R5 so should never get hot. A simple multivibrator should not be powered with more than 5V since the emitter base voltage can exceed the break down voltage. Even so, I do not see how the current would...
  20. duke37

    AC Compressor blowing fuse

    Congratulations. Now you are experienced, you could try to find shorts in a combine harvester where the rodents have had a field day and the wires are fitted inside a vibrating tube.
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