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  1. duke37

    tachometer

    I do not know whether I can help as this is not my expertise. Since you have a gearbox, you could use a Hall effect device to give a frequency output. This frequency can be turned into a voltage with a LM2917N. If you wish to engage a gear when two shafts match, then do the same for the...
  2. duke37

    BMW D12 Marine Diesel rectifier/regulator project

    Zener diodes can have a wide tolerance of voltage. You could get many and find one to suit you although if they are from the same batch, they might all be similar. The zener may be dissipating more than it should with such low resistances. How hot does it get? There are adjustable zener...
  3. duke37

    Help Measuring Speaker Ohmage

    The impedance of the basic spaker can never be below the resistance, the reactance has to be considered. This will go up and down depending on the frequency, the resonance of the speaker, the effects of any crossover network and the way it is installed. Hi Fi magazines often give plots of...
  4. duke37

    Help Measuring Speaker Ohmage

    Nice pictures. The reading looks to be 1.5 * 10 = 15, a reasonable value, if a bit high. The impedance of the speaker will be a combination of resistance and inductance so resistance is only a guide.
  5. duke37

    SCR S838

    I doubt if you need anything special, with a 12 or 24V charger, 200V would be adequate. The current specification should be several times the charger output current.
  6. duke37

    How would you modify this circuit to transmit audio data

    Seems like a very strange circuit. Look up Faraday cage. Morse code is sent by turning a signal on and off. Music or voice needs a system where the output is proportional to the input signal. You will need a linear modulator. A LW transmitter of this power would be illegal in the UK.
  7. duke37

    Automated Lead Acid Battery Capacity Tester

    What is the effect of discharging a battery intermittently? Even if the mean current is correct, the pulsing current with a switching design may affect the results. You could use a main resistor to give the current you need at the highest voltage and add resistors in parallel as the voltage...
  8. duke37

    Convert resistance ladder

    You could perhaps convert the resistance to a voltage by feeding in an accurate current and then use a LM3914 bargraph display chip in dot mode to switch in what resistors you want in the output. Some stable voltages will be required.
  9. duke37

    BMW D12 Marine Diesel rectifier/regulator project

    Did you find if the power diodes or the regulator were at fault?
  10. duke37

    88V to earth from secondary of 12V 10A power supply....

    When you say 'different supply' do you mean a different power supply or different source. Check the resistance between the mains input terminals and the output terminals, it should be open circuit. A switch mode supply may not like being turned on and off often as it has a large input...
  11. duke37

    Speed control single phase induction motor.

    With a low powered motor driving a fan, the best soluton is to use a dimmer as Harald has said. You can get one that plugs into the wall and the fan will plug into that. Simple safe and cheap. The dimmer varies the effective voltage by chopping the waveform with a triac.
  12. duke37

    Help with a UPS circuit

    That light blue furry thing to the left of the relay looks interesting!
  13. duke37

    Need help downgrading amp to lower power

    If you insist on using a high volume setting and limiting the voltage with the regulators, you will need to dissipate extra power so getting more heat - not a good thing. To dissipate this heat, use Tom's solution of an external resistor in series with the speaker, 10 ohm 5W should be enough...
  14. duke37

    88V to earth from secondary of 12V 10A power supply....

    In the UK we have PME (phase, multiple earth?) where the neutral is connected to local earth and everything is bonded together in one premises. This is not 100% reliable. 1. A grain dryer developed a fault, line to local good earth, and this pulled the neutral up to 100V or so. Thus other...
  15. duke37

    MOSFET IRF540A circuit.

    I looked on the Farnell site fot the first time and selected 'logic level mosfet' The STP40NF03L (30V 40A) with threshold of 1.7V may do.
  16. duke37

    MOSFET IRF540A circuit.

    The IRF540 has a threshold voltage of about 3V and needs considerably more than this to turn on fully. They work well on 10 or 12V. You will need to find a FET which will turn on with 5V, they are available. Or use a resistor feeding a junction transistor.
  17. duke37

    Speed control single phase induction motor.

    Yes but .... If the load decreses as the speed comes down, such as a fan, then this could work. If the load torque is constant, the currents and heat in the motor will rise and, due to the reduced speed, the cooling will be less. If the motor is small with shaded poles, it will be...
  18. duke37

    Reverse the voltage?

    I had a look at the MLX90316 data sheet, it seems to have a clockwise and anti-clockwise setting. Would reversing the direction do what you want?
  19. duke37

    Need help downgrading amp to lower power

    If the speakers are a pair, they will have the same specification. You will not damage the speakers if you drive with care and not use excessive volume. To halve the peak power of the amplifier, reduce the supply voltage to 70% of that specified. Power is proportional to the square of the...
  20. duke37

    Using a short circuit as a switch.

    The battery will be discharged - I hope you are rich! The thickness of wire will not make much difference, the current will be limited by the battery internal resistance. If you try this with a lead/acid batery, all sorts of exciting things can happen.
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