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  1. duke37

    Relay switching

    There needs to be a diode across the relay coil to protect the transistor from exceedingly high voltages. The mosfet does not need a negative voltage, it needs the gate voltage the same as the source voltage.
  2. duke37

    Beginner questions..

    What parts do you need? There are many suppliers in the UK, most will post but Maplin and RS have retail outlets that could be local to you. Maplin RS Potts, Derby (shop only) Cricklewood electronics CPC (Farnel) Bowood (Chesterfield) etc
  3. duke37

    Android Device overheating due to Capacitors

    Electrolytic capacitors have a temperature rating, 85C or 105C. If the faulty capacitors are 85C then 105C capacitors will help but the temperature should be kept as low as possible.
  4. duke37

    Help me to understand this circuit

    Do not see a zener diode, surely D1 is a Schotky diode. Is this a buck convertor?
  5. duke37

    Ampacity of brass/thickness of brass wire needed

    If the wire is pure copper, it will have the same resistance as other copper wire but is more expensive than enamelled magnet wire. If the current is very high, the temperature can be high and will burn the varnish off. Just get wire which is thick enough to take the current and will have an...
  6. duke37

    Electromagnet V vs Amp vs Turns?

    The field will be proportional to the ampere-turns and will need a certain power. Fill the spool to minimise the power. The limit will be due to heat generation, a short term overvoltage can be used if necessary.
  7. duke37

    Wireless Inductive Coil - How does the transistor make it work ?

    The coil you have is in fact a transformer with the centre tap connected to the supply. The transformer works like a see saw, when one end goes up, the other end goes down. At switch on, some current will flow into the base and turn the transistor on, this will drop the collector voltage so the...
  8. duke37

    Wireless Inductive Coil - How does the transistor make it work ?

    The circuit in #1 misses one critical component, this is the resistor. The coil produces positive feedback to make the oscillator. The coil is inductive and so the collector current rises linearly until the collector current reaches that which the transistor can supply with the base current...
  9. duke37

    Motor Speed Controller

    What is the motor, there is a plethora of types. There should be no loss of torque at low speed but the motor may overheat due to less cooling. With a permanent magnet motor, the unloaded speed will be proportional to voltage. Some motors have strong cogging so they will not run sweetly at very...
  10. duke37

    Need help and ideas

    Yes, it is possible, I have done it to power an audio system from the USA which was plugged in to the UK power and went fizz. I used the alternative battery input which still worked. Make one or more wooden batteries to fit the battery holder. Place a sheet of tin plate at the positive and...
  11. duke37

    Capacitor across a solenoid valve. Why?

    Are you sure it is a capacitor and not some form of voltage limiter. As you know, a diode is normally used but this needs to be connected the right way round and will slow the release of the valve somewhat. The higher the voltage that is permitted on switch off, the faster the current drops.
  12. duke37

    Is there any particular reason this won't work? Thanks

    R2 is also wrong.
  13. duke37

    I need to power a synthesizer with a battery...Please Help :)

    The device will take as much power as it needs so long as the voltage and polarity are correct. Too much voltage or wrong polarity is a sure way of killing the device.
  14. duke37

    Milliamp power supply question

    But you must use AC or DC as apprpriate and, if DC use the correct polarity.
  15. duke37

    Calculate radius of a copper wire

    There must be some units for resistivity. I tend to use basic S.I. units for calculations Derive an equation for the resistance of a circular wire of nominal length and diameter, Calculate its volume. Power dissipated is I*I/R so you can calculate the resistance and solve the equation you derived
  16. duke37

    Capacitor charging

    To find the resistance of the voltmeter, measure the voltage of a battery and then measure again with a 1MΩ resistor in series. If the resistance is 10MΩ, the reading will be low by about 10%. If the resistance is 1MΩ then the voltage indicated will be half the original. I have a cheap digital...
  17. duke37

    Ampacity of brass/thickness of brass wire needed

    According to my calculator the ratios are 3.7:1 Wires can be obtained with various coloured insulation.
  18. duke37

    160 KHz Oscillator Transmitter

    Is 160kHz in the long wave band? I think that R1 should be somewhere between 10k abd 100k, a low value will damp the circuit. The audio input should have a RF bypass, it is a grounded base circuit. There should be an emitter resistor to take the feedback, what is R3 for?
  19. duke37

    Ampacity of brass/thickness of brass wire needed

    Why brass? The colour will be determined by the insulation. Look up the resistance of the brass and get the area of the wire to be in proportion to copper wire for the current you want. The current limit is dependant on the voltage drop and on the heat produced. A bit more information would help.
  20. duke37

    How do constant current loads work and how to make one

    At a rough guess you should be able to make a 1000V 1A supply for under $10000. A bargain.:)
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