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  1. duke37

    Transmitter Pi Tuning and Loading network design

    50Ω is chosen for convenience. Older transmitters used to use higher loading resistances, possibly 400Ω. A half wave dipole will show a centre feed resistance of about 50Ω and if fed with 50Ω cable, this what the transmitter will see. A valve in a transmitter may need a 10k load and a low pass...
  2. duke37

    Transformer Mystery

    This could be a very high voltage transformer and could be dangerous as said before. The primary and secondary appear to be on separate bobbins which would support this. Measure the resistances between the pins to see which where the windings are connected. The primary may be in two sections for...
  3. duke37

    I can't find a replacement potentiometer

    Gryd3 "Can you tell lack of experience is asking this Q?" I have no experience of breast pumps, do you? Duke37
  4. duke37

    I can't find a replacement potentiometer

    It looks to me that the pot is connected to the three centre pins. The outer two look to be connected to the case for screening. Just get a 10k pot, but linear or log?
  5. duke37

    Static inverter design

    The CMOS cookbook p334 by Don Lancaster shows a simple way of generating three 3 phase singals. It uses a 4018B and needs an input of six times the output frequency (2400Hz). The three transfomers will probably use an iron core but this will be much smaller than for a transformer for 50Hz. The...
  6. duke37

    3 Phase rectification problem

    If the capacitor is failing due to overheating, you are passing too much current. If the capacitor goes short circuit, it will cause the input fuse to blow. You could try a much larger capacitor to share the ripple current. Do some calculations to find the dissipation in the capacitor with the...
  7. duke37

    Power Resistor As Heating Element

    1. You will need to determine the output current which the microcontroller can provide. I have never used a microcontroller so have never bothered to look up their specifications. I very much doubt that a microcontroller will provide anywhere near the power required. 2. The current and voltage...
  8. duke37

    AC Diode

    This was my idea using a relay. Sorry about the poor quality, nothing seems to work here since my trip to hospital! An AC relay may be hard to find but you can use a DC relay fed through a bridge rectifier.
  9. duke37

    Temperature control

    I suggest that you use a thermistor to detect the temperature and find the resistances at the temperatures that you want. Design an op-amp circuit to give the outputs that will give 0V at 95C or below and 5V at 90C and above. You will need a power supply for the amp, this could perhaps be stolen...
  10. duke37

    AC Diode

    That is also what I thought so it is why I suggested a way of doing it with relays if his pump could not run on DC.
  11. duke37

    Changing Signal Frequency And Frequency Overtones Respectively

    Welcome to the forum. A resistor will not help, this is a complex job. You could analyse the incoming signal using a fast computer running a fast fourier transform. This would give the frequency of the fundamental and the harmonics. The frequencies could then be changed and the signal...
  12. duke37

    AC Diode

    Will your AC pump run on DC? (i.e. a universal motor). You could use a couple of relays, fed from each supply which are energised to send the AC to the pump. The relays would be cross connected so that when one is energised, the other is inhibited. You may be able to get away with one change...
  13. duke37

    Power loss in battery

    The dimensions of the wire are given as cm and mm. Chose one or the other but even better, use the basic unit of metre. There is no dimension defined for the wire so the value given is useless. You will need to calculate the resistance of the wire and then the power loss V*V/R. Assume the...
  14. duke37

    Trouble with solder

    You will not be able to solder to aluminium or chromium due to the persistent oxide layer. You may be able to spot weld a wire with suitable equipment. What is the material? Iron/steel can be difficult but an acid flux helps.
  15. duke37

    Shunt motorcycle regulator

    One problem with the circuit is that it uses a zener diode which will have a fairly wide tolerance. You may be lucky and get the right voltage or you may not. A TL431 can be used instead and works as a variable voltage zener so the output could be set to 14V. It should be connected direct to...
  16. duke37

    Taming an unstable power rail

    An infra-red temperature detector could estimate excess current consumption.
  17. duke37

    Taming an unstable power rail

    Electrolytic capacitors can arc over internally particularly if they are overvoltaged. This can be quite exciting with large high voltage capacitors.The output voltage will therefore drop and the capacitor will recharge. Check for warm capacitors. If this is the cause, then adding capacitors in...
  18. duke37

    Shunt motorcycle regulator

    I do not see a 2 phase circuit. The first circuit is single phase with a full wave rectifier and the second circuit has a half wave rectifier. I am not familiar with motor cycle alternators but car alternators have a built in leakage inductance. This has a reactance which is proportional to...
  19. duke37

    circuit stops responding after few seconds

    Seems strange to me that you use Schottky diodes when almost any common diode would do. The 1N5819 is limited to 40V but you do not say what the input voltage is. You also do not say what transistors are used. I would think that a component is running too hard and is heating up, possibly T2.
  20. duke37

    Uses of inductors

    An inductor stores energy in a magnetic field, it follows that the current is reluctant to change as power has to be provided to do it. Thus, placing an inductance (choke) in a power supply line will tend to smooth the current. A capacitor stores energy in an electrostatic field depending on...
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