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  1. duke37

    12V 4A supply for a peltier heat pump

    I wonder whether anything sophistcated is needed. I would think that a transformer and rectifier would be adequate. Doesn't the Peltier behave like a resistance?
  2. duke37

    Oh what to do with a Tetrode tube????

    Tetrodes are kinky! Tetrodes are used to provide output power as said, they are used for audio amplifiers and radio transmitters. You will need the type number to determine the correct operating conditions. Anode voltages can go from 300V to 10kV. Not something to be trifled with.
  3. duke37

    Relay "Ratings"

    The rating of a relay is based mostly on the ability of the contacts to switch off the current. The higher the voltage, the bigger the arc so the same relay may be rated at 120V, 10A and 240V 7A. Switching AC is easier than DC since the arc is extinguished twice per cycle. In the case of DC...
  4. duke37

    Possible current drop-off in two merged power adapters?

    You could try the TV on a car battery if you have a car!
  5. duke37

    Direction of AC motor

    The motor has brushes so I do not think that it is of the induction type with capacitor start or start/run. Any capacitor is more likely to for interference suppression and will have no effect on the motor behavior. Is it connected across the supply? Motor capacitors will have values of uF...
  6. duke37

    Direction of AC motor

    If the blade has a slight twist at the cutting end, it should run in the direction that lifts the grass from the ground.
  7. duke37

    1Hz timebase question

    If you put the crystal in a suitable circuit, it can be adjusted to the correct frequency, then you only have variables such as temperature and power supply voltage to upset things.
  8. duke37

    Direction of AC motor

    If the motor has brushes, then it will be a series connected 'universal' motor. To reverse rotation, you will need to change over the brush connections OR the field connections. You could try it out with a light bulb in series with the supply to check that nothing is untoward. Are you sure...
  9. duke37

    need help! :0 4011 NAND gate

    I do not follow your description. Sketch out the circuit to show what you did. You do not say whether the two power supplies have a common reference which will be needed.
  10. duke37

    Can anyone tell me what is meant by a reference signal and where it comes from?

    In this case, a highly accurate frequency standard is not necessary, just use the energising signal as the reference as you say. You will need to get the phasing right.
  11. duke37

    measure a voltage across of a dc motor

    If the motor were 100% efficient, it would take no current with no load. In practise, there is resistance in bearings, air, copper etc so power is needed to run the moter even when there is no power coming out. As load (torque) is increased, the motor slows and the current rises to provide the...
  12. duke37

    Can somebody explain this simple circuit please?

    The collectors will swing from about 0.2V to 7V. The negative side of the capacitor will swing 6.8V but the maximum voltage at the base will be 0.6V (the base conducts) so the swing will be from 0.6V to -6.2V. Note that 6.2V negative on the base is close to the limit for normal silicon...
  13. duke37

    Can somebody explain this simple circuit please?

    Look for information on a multivibrator, there should be lots of references out there. Polarised capacitors can be used as long as the polarity is not reversed. They have the advantage that they are smaller and cheaper than non-polarised capacitors. You can make a multivibrator or similar...
  14. duke37

    High voltage rails for class D amp?

    The two amplifiers will have the same output if they are set up to have the same gain. The 80V amplifier will be able to supply twice the voltage of the 40V amplifier so will have four times the power capability. You can get more power out with a low voltage supply if you have a low...
  15. duke37

    Three Phase Rectifier Capacitor

    Voltage ripple I did not calculate the voltage ripple, I just chose a value at random to show how the equation is used.. It is up to you to determine what ripple can be tolerated. As I said, you may be able to run with the ripple direct from the rectifier. Why does a welder need a low ripple?
  16. duke37

    measure a voltage across of a dc motor

    There are no details of the type of motor, if it is a motor with a commutator, it will generate a voltage when it is turning which can upset your measurements. Get the PWM circuit working into a resistor and then substitiute the motor. There seems to be a negative spike in the waveforms, a...
  17. duke37

    Three Phase Rectifier Capacitor

    The ripple voltage can be calculated with the formula I gave earlier. Why do you need to control ripple? There will always be a positive voltage with three phase full wave rectification and the inverter could be controlled to give a constant output. The capacitors would then only need to bypass...
  18. duke37

    LEDs in series to 240V?

    As gorgon says , the capacitor will hold the voltage up, near 340V. If you eliminate the capacitor, then the average power in the leds will be less than halved. The leds will flash but this will not be noticed by humans. Don't know about fish. You should always use a series resistance to...
  19. duke37

    Three Phase Rectifier Capacitor

    This is well outside my experience! If you rectify the three phases with full wave rectification you get six pulses per cycle. At 50Hz (?) this gives 3.3ms between pulses. The output voltage will be about 550 and with 5% drop between pulses, that will be 27.5V. P=I*V so I=100k/550 = 182A...
  20. duke37

    how the circuit work!

    I think the receiver is a superregenerative circuit. The current through the receiver will vary depending on whether a signal is being received. This will vary the voltage across R3 and the variation is passed through C4 to Q2 for amplification. If L2 is not screened, there may be sufficient...
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