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  1. duke37

    checking Chinese capacitors

    I use an analog meter in series with the capacitor and high voltage power supply. If the meter reads zero, then there is no leakage. The meter on an appropriate voltage range will limit the current. I have also used this method to measure the capability of hgh voltage diodes.
  2. duke37

    My air purifier fans won't turn anymore, making humming noise

    I used to service tape players for the blind and saw a lot of these motors. If found early, they could be cleaned and relubricated but if the shaft was worn, they will soon fail again. I used various lubricants and settled on engine oil, I have often used a drop from the end of my dipstick to...
  3. duke37

    Missing resistor in a voltage divider network

    Not quite 7K ohms. It is 7kΩ, temperature does not come into it.
  4. duke37

    Missing resistor in a voltage divider network

    So, what is the answer?
  5. duke37

    Missing resistor in a voltage divider network

    Each op-amp switches at 1V difference from the one next door. You are told this in the question. Why were you told this if it should not to be used? You do not need the actual current, You can do this without calculating it, You do need to know that voltage is current times resistance. Here the...
  6. duke37

    Microwave cooling fan help

    If the fault were due to a fork being left in the microwave, it is likely that the RF generator has been damaged. The motors are maiins voltage and can be tested outside the microwave. They may not run in the microwave due to a fault elsewhere.
  7. duke37

    Missing resistor in a voltage divider network

    You have five 1k resistors in series with 1V across each so you can work out the current. The voltage across Rx will be the difference between 12V and the resistor chain voltage. All this assums that the op-amps take no current.
  8. duke37

    12v 0.5A auto trickle charger

    Or try an old style charger which consists of nothing more than a transformer and rectifier. If the battery has been sitting at 5.8V for a long time, then the plates will be sulphated and the battery will have no capacity.
  9. duke37

    Regulator to limit 12v DC current

    You need sufficient voltage to run the circuit. 1.25V across the sense resistor and a couple of volts across the 317 plus the voltage across the output. 6V may be sufficient. High input voltage will dissipate power and the 317 will get hot. How do you pass current through distilled water? Water...
  10. duke37

    Reducing battery charger output

    No, the resistor will reduce the current but will not restrict the voltage. If you charge through a resistor, keep a record of the battery voltage and stop charging when 14,4V is reached, If the battery has been over discharged it may be necessary to use a high voltage to change the electrolyte...
  11. duke37

    I am building an electric fence driver and need to know if has too much or too little power

    Electric fence drivers vary widely in the power of the shock. They are specified in terms of energy rather than volts or amps, A small fence would be adequatelt powered with 0.1J but a long fence in Australia may use 10J (but Australians are tough). The energy is normally provided from a high...
  12. duke37

    Reducing battery charger output

    My first thought is why do your batteries need charging? It would be better to make sure the vehicle system is working properly. I last used a charger about thirty years ago when the brushes in my car dynamo had worn out. The charger is now used to drive a coil winder. 12V lead acid batteries...
  13. duke37

    Load cell + hx711 = drifting value

    I would make a dummy load cell with four sooper-dooper resistors to see if the rest of the instrumentation is stable. Add a high value resistor to check calibration. If this system is stable, then you will have to get a better load cell.
  14. duke37

    Car Thread

    A 2014 car is not old. I have recently wound a coil for a 1900 car with low voltage ingnition. Do not waste the planet's recources, go to the local scrap yard for any spares.
  15. duke37

    convert Battery powered alarm to mains with battery backup?

    I would suggest using a 6V lead/acid battery and buy or make a power supply, set to 6.9V to continuously charge the battery.. Burgler alarms which have passed through my hands use this method at 14V. A pair have been used to supply 24V to a station clock system. You may be able to get a used 12V...
  16. duke37

    RED LED Darkroom light

    Ny niece is thinking of taking up balck and white photography. Low power incandescent bulbs seem to be thin on the ground so I was wondering if a light based on red leds would do the same thing as a filtered incandescent light in a darkroom. Would they affect enlarging paper? How many leds at...
  17. duke37

    Flyback Diodes

    I think you are using too posh a meter. For this sort of test I use a 3V Taylor analog meter which shows about half range when a silicon diode is tested in the forward direction, a germanium diode gives a greater deflection. The resistance range setting makes little difference and there is...
  18. duke37

    Flyback Diodes

    If diodes are fitted, then the resistance will differ depending on the polarity of the meter. An extra diode will do no harm but must be connected the right way riound as must be the power supply.
  19. duke37

    Repairing a massage recliner

    If it is a brushed DC motor, check the brushes. Is power getting to the motor? Give details of the motor including a photo. What country are you in and where was the recliner made?
  20. duke37

    The Dark Side

    Those are pnp transistors and if they are germanium will withstand 7V. Silicon transistors should not have more than 6V on the base/emmitter junction so in this case limit the power supply voltage to 6V.
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