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  1. duke37

    Heathkit IP20 Power Supply

    If one output transistor is used,then the emitter resistors R49 and R50 should be connected in parallel. It would be better to use two output transistors to spread the heat better. I do not fully understand the action of R23 since transistor X3 will try to compensate. Use a couple of Schottky...
  2. duke37

    Small motor project - ferris wheel

    You will need to measure the torque required due to bearing friction and load offset. There are small DC motors advertised with gearboxes already fitted. If you wish to go second hand, the a windscreen wiper motor would be plenty strong enough. You will need a 12V supply of a few amps such as...
  3. duke37

    Small motor project - ferris wheel

    At this low speed, the power required will be low. The motor will need to provide sufficient torque to turn the wheel which will depend on the bearing friction and the weight offset, you will need to measure this. Total weight will not be a problem if the weight is balanced and the bearings are...
  4. duke37

    The resistance range of a potentiometer

    As you describe it, the potentiometer will be connected across 12V and the output will be taken from the slider. The output can then be varied from 0V to 12V. There will be a voltage drop due to the resistance of the pot and the current drawn by the ECU. If the pot resistance is less than one...
  5. duke37

    Output of (voltage multiplier??) circuit

    I think you are right. It can be looked on as two voltage doublers, one stacked on top of the other. To get an idea of the output waveform, you will need information on the frequency, capacitor values and load. With no load, what will the waveform be?
  6. duke37

    Heathkit IP20 Power Supply

    If silicon transistors are used, I would be concerned about the voltage across R23 which is not an ordinary resistor. Some modification to the circuitry may be necessary. What thinkest thou, Kris
  7. duke37

    Is there a MOSFET that turns OFF when voltage is applied to gate?

    Do you want both head and fog lights to be off together? The circuit as shown always energises one or the other.
  8. duke37

    making a tiny heat element

    I made a cutter for model aircraft foam for a friend. We tried Nichrome wire and also stainless suture wire and violin string wire. Fishermen use wire also I believe. You do not need to have wire which will resist oxidation at very high temperatures. Constantan is another source, used in...
  9. duke37

    Heathkit IP20 Power Supply

    Silicon transistors will possibly do, even a single one. I do not understand the point of the thermistor R23 which would have more voltage across it. It may be there to shut down the supply when the temperature goes too high.
  10. duke37

    Triac Based Inverter

    I do not see how this can be used as an inverter, It looks like a phase angle power control to me.
  11. duke37

    230V led driver, which one has low failures?

    During normal running, the current will be controlled by C1 and R1, a voltage drop across R2 will do nothing much. A zener across the led will either take all the current or none at all depending on the relative voltages of the zener and led. By defining the voltage across R2 and led in series...
  12. duke37

    Electrical generation in power stations - how AC Hz and voltage fluctuates

    Yes, I was told to set a synchronous clock at midnight on a Sunday when demand was low and the frequency and time would be set.
  13. duke37

    230V led driver, which one has low failures?

    The diagram which you show is not what I recommended. The zener should be connected across R2/led1 pair. A value of 6V to 10V or so will limit the peak current on switch on. I do not see how to protect the whole circuit from over voltage, just make sure R1 and C1 are capable of withstanding any...
  14. duke37

    transformers back to back - why won't work?

    There are at least half a dozen back to back transformers between generation and use, so it is possible. The power limit is determined by the resistance of the wire and overheating thereby. A bigger core allows fewer turns of thicker wire so a higher power output. Small transformers often have...
  15. duke37

    230V led driver, which one has low failures?

    Many led displays are multiplexed so I would think that the intermittent current should not be a problem. I have a clock at least 20 years old still working well. You could consider keeping R2 and replacing D1 with a zener to limit the turn on current, this could be as high as 150mA if the...
  16. duke37

    230V led driver, which one has low failures?

    To use a resistor to limit the current will need about 50 times the power to be dissipated in the resistor over that dissipated in the led. This may not be a cost problem but the heat will need to be removed. I have an aversion to electrolytics for reliability. I would therefore go with...
  17. duke37

    transformers back to back - why won't work?

    I am no expert in this field but used to travel to work with an electrical engineer. I have tried to find out without success how to determine which winding may have a shorted turn and we discussed transformers quite a bit. The energising AC produces a current which is 90deg out of phase. This...
  18. duke37

    transformers back to back - why won't work?

    I would disagree with this statement, the magnetization depends on the voltage, not the AC current drawn. If however you rectify the output in such a way as to put DC through the output transformer, then saturation could occur.
  19. duke37

    Pie Network , Transmitter Tuning and Loading Questions

    From what I see, the 6T9 will be similar to an EL84 audio valve or 5763 or 6BW6 transmitting valves. You should run at 250V and 40mA. The anode load will be about 6k. C2 will be much less than 1000pF at 7Mhz. You can find the equations and calculate it. The voltage will be fairly low so an air...
  20. duke37

    Pie Network , Transmitter Tuning and Loading Questions

    You must NOT use maximum output, you must keep within the valve limits. The normal method of tuning is to set C1 to dip the anode current with C2 maximum, then reduce C2 a little and set C1 back to resonance. The current will then be a little more than previously. This is repeated until the...
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