Search results

Search Forums New Posts
  1. duke37

    DC Welder off Car Batteries

    An inductance in series with the arc can generate a high voltage if the arc dies, with AC the arc extinguishes twice per cycle this will allow it to restrike. Putting a diode across the arc will suppress the high voltage but this may not be a problem with a DC source.
  2. duke37

    need help to understand a circuit

    The transistors Q1 and Q2 are presumably silicon devices and need 0.7V base/emitter to turn them on, therefore 1.4V is needed between the bases to eliminate a dead band. The 1.4V is generated by supplying a current through two diodes which drop 0.7V each similarly to the transistors.
  3. duke37

    Ultrasonic Transducers

    I do not understand how the circuit is supposed to work. I would think that there should be a short pulse and then a circuit to measure the time delay on reception. Thumping a resonant transducer at a low frequency will give a short train of high frequency output at its resonant frequency...
  4. duke37

    Metasonix Thryratron Synth; Op Amp Pin out?

    A musical scale is not linear. Each semitone is about 6% different from the next one (2^(1/12)). This means that a linear change in voltage needs to be changed to a linear change of current and then changed to the logarithm by putting it through a semiconductor junction. Transistors or...
  5. duke37

    Ultrasonic Transducers

    A couple of comments. The electolytic capacitors are the wrong way round but this could just be a drawing error. At 40kHz, you could go for smaller non-electrolytics. The led shoud be connected in the collector not the emitter of the transistor. You may not be getting sufficient voltage...
  6. duke37

    DC Welder off Car Batteries

    I cannot get at the digikey site. Why not sketch the schematic and then scan it or photograph it and attach it to the thread?
  7. duke37

    Micro Switch help

    The standard microswitch body is 27.8*15.9*10.3 (Maplin) I have some old catalogs here Maplin GW71N RS 159-4411 (cheaper but they come in fives) Check that I am correct.
  8. duke37

    Micro Switch help

    That looks like a standard microswitch. There are miniature and subminiature switches. What is the size? The one you show seems to be a make only, most are change over and so have three connections.
  9. duke37

    Band-Pass Filter Help

    I did a Google, there is a circuit there using a LA3660 for a 5 band equaliser.
  10. duke37

    Band-Pass Filter Help

    There was a question on the homework section recently to evaluate a filter. I was interested since it was so simple. As shown it is a band pass filter passing audio frequencies. I did a simulation in 5spice. I have 'Electronic filter design handbook' by Arthur B. Williams. This deals with...
  11. duke37

    stepping down voltage twice

    The power supply will drop its voltage under load, perhaps this goes too low. The regulators have a current limit, perhaps the current taken through the 7812 is over 1A. The regulators have a power limit, perhaps the 7812 got too hot and it decided to lie down !
  12. duke37

    DC Welder off Car Batteries

    A diode passes current in one direction only. The current rating should be well in excess of the average current for safety. The diode should have a voltage rating sufficient to stop any reverse current. With a supply of 25V, go for 100V rating. Welding involves bad connections and pulses...
  13. duke37

    How to rectify ac to run a dc motor?

    eKretz The idea of the shunt was to look at the current waveform. Current will only pass when the voltage supply is above the back emf. This will occur for only a short time. Thus your average of 300mA may give many times that peak. If the loading is increased the current will have risen...
  14. duke37

    Looking for transmitter

    It may be better to use sound, with a slower speed it will be much easier to time the signals. I believe the military used this in WW1 and still use it. There will still be problems with obstructions and sound propagation speed.
  15. duke37

    Home Brewed Oil Capacitor Rectification

    The microwave transformers that I have seen do not have an isolated winding which you will need. Rectifiers are cheap so go for eight or ten 1000V 1A diodes in series. In the early days, balancing resistors and capacitors were used but I think they caused more problems than solutions...
  16. duke37

    How to rectify ac to run a dc motor?

    Young may be right. The problem is not voltage, it is current. If the voltage is higher than the back EMF then the current will be high, this can be smoothed with the addition of a parallel capacitor or series inductance. Small motors are often run on rough supplies but big motors with low...
  17. duke37

    Home Brewed Oil Capacitor Rectification

    1000V at 500mA is 500W, this supply will be big and heavy. The trouble with voltage multipliers is that the capacitors are in series so that big capacitors are required to get the capacity. To get high voltages for electron microscopes, high frequencies are used to help this problem. You...
  18. duke37

    How to rectify ac to run a dc motor?

    The part of the commutator that is shown in the photo looks good. If there is a fault in the comm, then I would expect to see some signs of arcing between segments and I would not expect it to run nicely at low voltages. You have not commented on the brushes in the photo. It looks as if they...
  19. duke37

    High- Voltage Adjustable Regulator

    You cannot get much more voltage out of a winding than it was designrd for. The core will go into saturation. Putting the secondaries of two transformers in series may work but you are relying on the insulation in the transformer being adequate. I would not do it. Running a transformer in...
  20. duke37

    N channel Mosfet

    You could look up the data, like I did. The transistor is a high voltage, medium current fet. It has a maximum votage, source to gate, of +/- 30V. Below 30V there will be no current passing in a diode test. At some point above 30V, current will pass as you ruin the gate insulation and kill...
View older results
Top