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  1. duke37

    AC Voltage Amplifier

    The 2N2222 is listed at 60V top whack. 100V will do it no good. You are overdriving so that the transistor is turning fully on and fully of so generating a square wave. You do not have a negative supply so how do you get a negative voltage? A symmetrical output waveform could be obtained by...
  2. duke37

    5v linear voltage regulator design problem.

    Is the car positive or negative earth? Is it 6V or 12V? Does it have a dynamo or alternator? When did alternators come in? I have never heard of one made for positive earth. I will look into these bypass caps you speak of. I added a small filtering cap after the transistor as I figured perhaps...
  3. duke37

    Voltage Fluctuation

    You probably have a massive capacitor, called a battery. The problem could be voltage drop along the cables. Try connecting the pump directly to the battery.
  4. duke37

    Running a motor at lower voltage - what will happen?

    I do not see any danger. It will not explode but if it is stalled the commutator may be damaged by uneven heating. The current taken by the motor will be dependant on the torque and the heat dissipated will be dependant on the current. Use the finger test ! Ensure that the power supply is...
  5. duke37

    Rectifier Help Needed

    I met a retired electrical engineer at the supermarket a couple of days ago. He said the Bantam alternators were very reliable. To get maximum output, first check that the magnets are OK which they will not be if the alternator has been dismantled. I would forget the centre tap and fit a bridge...
  6. duke37

    5v linear voltage regulator design problem.

    The 7805 is NOT a transistor, it is a regulator. It may be small but it is perfectly formed. It is not dropping 5V. From 12V it is dropping 7V and from 14V it is dropping 9V. The TO220 cased device can dissipate about 2W in free air or about 25W on an infinite heat sink. With no load it should...
  7. duke37

    5v linear voltage regulator design problem.

    All vehicles since about 1950 have used negative ground and this should be the reference point for all equipment. It follows that to reduce voltage you will need a positive voltage regulator such as a 7805 not the negative 7905 regulator.. This was probably running on reverse polarity so it is...
  8. duke37

    5v linear voltage regulator design problem.

    Give us a sketch of the circuit. Did you use a regulator or transistor or a combination of the two. Was the supply connected the wrong way round or were the regulators killed by voltage transients?
  9. duke37

    Please let me know your idea about this circuit

    You have four waveforms on the scope, is this actual voltages or simulations. The two pairs of waveforms have vastly different time bases, what is the red square? The top waveforms look reasonable with the output sinking slowly, being pulled down by R4. A simulation will assume that the supply...
  10. duke37

    grounding in electronic circuits

    The layout of ground wires can be complicated. A computer used to record analogue signals can have three grounds, one to connect to the case to protect the operator from shock, one to run the digital signals and one to reference the analogue signals. These are likely to be connected together at...
  11. duke37

    Testing car battery

    Burglar alarms often use a 12V battery and have a power supply which is set to 13.8V. They are safe to work without the mains connected and will not discharge the battery in this condition. The 13.8V is chosen to be suitable for the temperature in the UK. You will need to find out the voltage...
  12. duke37

    How to control 700 solenoids?

    You could use multiplexing where the positive line is switched as well as the negative line. The lines are made into grid. The number of connections is proportional to the square root of the devices, so 60ish. The problem here is that each solenoid only receives a signal for part of the time so...
  13. duke37

    Caustic Corrosion on Water Level Sensor

    I have used Waxoyl which is a wax diluted with a petroleum spirit. This is sold for protecting the undersides of cars from corrosion. I have used it on electric fence energisers and outside nuts and bolts. It can be removed with white spirit or paraffin. When fully dry it is a stiffish wax. It...
  14. duke37

    Heating Element Problem

    The resistance should ideally be infinity - but it never is. You should be able to stand 10000Ω (10k) assuming that nothing else in the house is leaking. Measure the resistance from line to earth at the plug without the heater connected to see if anything else is leaking.
  15. duke37

    Calculating frequency

    This seems unrealistic to me so I have not done any calculations. To get down to 0.375Hz, you will need a much bigger capacitor and thousands of turns. 6.5 turns of 0.5mm diameter over 60mm length is a helix not a coil ! If you are looking for 375MHz, then the capacitor will not work, it will be...
  16. duke37

    Heating Element Problem

    It seems you have earth leakage. Measure resistance from live to earth, preferably with a high voltage. The leakage from live to earth is the most likely problem but it can also occur if the neutral has deviated from earth. If you find some leakage, disconnect each part and see where the fault...
  17. duke37

    OA79

    Would Schottky diodes be a suitable substitute?
  18. duke37

    Electric motor switch thing???

    Wires can often break inside cables. That mains lead has a serious bend at the end. Check whether power is lost if you gently wiggle the wire at the bend.
  19. duke37

    regulate fan speed

    Try some series resistors about 10Ω and 5W and see what speeds you get. Find a four way switch to select the resistor in the resistor chain.
  20. duke37

    Popper Pot specs?

    If the heater runs on 120V, them how can the fan get 19V if it connected to the same place? Hair dryers often have a 12V motor in series with the heater. I suspect that this is the case here but the diodes look small for 4A.
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