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  1. Merlin3189

    Confused about a DC Motor

    While I like Heavans description of DC permanent magnet motors, I would just quibble with one comment: I think that exactly the opposite is the case! To a first approximation and for most amateur people (eg. making electric powered models) the design process is based on the linear properties...
  2. Merlin3189

    Non-changing current with C-EMF

    And another annotation to a previous diagram to help see the cancellation of any magnetically induced EMFs.
  3. Merlin3189

    Non-changing current with C-EMF

    Thanks for the suggestion. I've used it for the attached diagram. If there were any changes in the current I, then you would be correct that the reactance of both inductances would add in opposition to the change in the current. But if we are assuming the current is constant, then the only...
  4. Merlin3189

    Non-changing current with C-EMF

    And your diagram would be like the attached.
  5. Merlin3189

    Non-changing current with C-EMF

    And the physical arrangement would be like this attachment.
  6. Merlin3189

    Non-changing current with C-EMF

    What I had in mind would look like the attached image. I've represented your Copper slab as lumped properties, resistance to represent the Ohmic resistance and pure inductance L1 to represent the effect of a magnetic field generating an emf. In the second circuit L2 and L3 represent this...
  7. Merlin3189

    Input impedance and Max RMS ac voltage

    A light-hearted explanation in response to DaveWalker5 It might be more correct to say that, "the inverse of the dimension of time is the dimension of frequency". It takes me half an hour to get to work, but the frequency of my going to work is not twice an hour or 24 times a day. My...
  8. Merlin3189

    Non-changing current with C-EMF

    I'm not sure why I'm reading all this, as I don't understand what you are trying to do or why! Yes, it's just an experiment, but even an experiment needs a reason (even a thought experiment.) And if the reason is to find out how much power is needed to maintain a constant current (answer...
  9. Merlin3189

    Common Base RF amp - CE feedback capacitor?

    Thanks for your comments. And may I say you've got a very interesting site. I've only just discovered it and I can see I'll be spending some time exploring & reading there. I think the answer to my questions about this circuit is to build it and have a play. When I look at it, it just...
  10. Merlin3189

    Faulty power connectors

    Having done some more work on these, it seems to me that the fault lies in the plastic used to mould the connector. Having removed all metal from it, I can put test leads into the vacant holes and get readings as low as 15kOhm - not exactly a conductor, but hardly an insulator. Since they were...
  11. Merlin3189

    Common Base RF amp - CE feedback capacitor?

    In my wanderings around the web I've just come across the TalkingElectronics site. In its vast compendium I latched on to the 27MHz section with descriptions of the circuits used in toy remote controls. I was intrigued by the connection of the receiver antenna to the collector of the Common...
  12. Merlin3189

    What is the purpose of the transfomer in this DC cicrcuit?

    Just for the sake of those interested, I think this is a blocking oscillator or relaxation oscillator. The autotransformer (the single tapped winding) provides positive feedback. When Ic reaches max or xformer saturates, feedback falls off then +ve feedback shuts of transistor quickly and...
  13. Merlin3189

    power rating of series and parallel circuits

    Something odd going on here. 7.5W in a 2.4 GOhm resistor would mean 134000 V across it. Even if at only 2.4 MOhm it is over 4000 V, which is at least conceivable, but you might still be more concerned about the Voltage rating of the resistors. In that case maybe a mixture with both parallel...
  14. Merlin3189

    How does shifting phase across frequencies work on the physical level

    One way of getting an idea about this is to think of an R-C circuit. If you apply a signal to a resistor in series with a capacitor and measure the Voltage across the capacitor, it obviously takes some time for the capacitor to charge up to the applied Voltage. (The actual time may be very...
  15. Merlin3189

    Why does longer probe cable reduces bandwidth

    I think this is why you use a x10 probe on the end of the cable. Then you can adjust the serial capacitor to match the cable (& input) parallel capacitance. Without a probe with serial capacitor, there is only parallel capacitance, which attenuates signals proportional to frequency and this...
  16. Merlin3189

    Find Fault in my built amplifier

    Is it just me who finds this circuit weird? DC Voltages left to right and signal bottom to top, took me a while to follow this circuit. Am I just old fashioned expecting circuits to read from left to right?
  17. Merlin3189

    Why was this equation required to be in metres before resolving?

    Just to be clear, the units are Ω x m not Ω / m The defining equation for resistivity is resistivity = Resistance x Area / Length , units Ohm x m x m / m or Ohm x m See http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity (Apologies that I haven't worked out how to write...
  18. Merlin3189

    Why was this equation required to be in metres before resolving?

    Chopnhack, what struck me about your post was the comment, "... to get resistivity of material is 0.156999 for that size resistor at 1 ohm..." But resistivity is not a pure number - it has units. Just like speed, time, weight, density, area and most of the quantities you come across. You would...
  19. Merlin3189

    [woo] Does anyone know of this breakthrough technology ?

    For what it may be worth, the report claims to be produced by "Junwei Lu" http://www.griffith.edu.au/engineering-information-technology/griffith-school-engineering/staff/professor-jun-wei-lu and "Chirag Panchal"...
  20. Merlin3189

    Faulty power connectors

    I'm not sure what I'm asking here! I'm just astonished and wonder if anyone has similar experience or thoughts about it. Out of a set of 15 power leads I have just tested, I found 4 faulty with a low resistance between the pins. They are about 3 years old, but show no signs of physical damage...
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