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  1. duke37

    Can't identify if transistor is PNP or NPN?

    On the resistance range, an analog meter usually puts a positive voltage on the black lead and negative on the red lead, this can confuse things. Do not use the lowest resistance range, this can blow delicate transistors. Just keep a known transistor to compare. If the transistors are being...
  2. duke37

    Grounding an output based on resistance

    You do not say what country you are in. In the UK you would invalidate your insurance and put lives at risk by messing with your car controls. I suggest you get a bicycle.:)
  3. duke37

    2 motors pushing an object. 1 motor goes bad... other keeps going... object breaks???

    You will need to supplly 7A for the series connection plus some for start up. It depends on the inertia as to how long the start up transient will last. You will NOT get 24V 15A. You either have 12V 15A in parallel (assuming they do not fight) or 24V 7.5A in series. As @dorke says, in series...
  4. duke37

    Determine the Vcbo of a germanium transistor and the voltage drop along the connected components.

    I just guessed, I would think that there will be a wide variation between transistors.
  5. duke37

    Determine the Vcbo of a germanium transistor and the voltage drop along the connected components.

    Why use a leaky npn germanium transistor in the first stage when silicon npn transistors are so common? According to your table the leakage will be about 12μA. If you wish to keep this configuration, you could by-pass some current with a resistor from the collector to 9V
  6. duke37

    Output Voltage Selector

    I suggested this in #2 but there is a significant voltage drop which is mostly eliminated with a hard turned on FET.
  7. duke37

    2 motors pushing an object. 1 motor goes bad... other keeps going... object breaks???

    If they are similar motors and similar loads, have you thought about putting them in series? Then the current and torque would be the same in each motor.
  8. duke37

    Output Voltage Selector

    Ah, I didn't spot that one transistor was up-side down.:( But the drive needs to enhanced? To turn them both on, the gate needs to be positive with respect to the source. What drive is needed when the source and drain are interchanged? It would help if the power supplies were labelled with...
  9. duke37

    Output Voltage Selector

    Q2 and Q3 are in series. There is no need for this, one fet should be adequate to switch 4V. When one transistor is on, so is the other so all you are doing is killing two transistors rather than one. To stop reverse current, you need one n channel and one p channel fet in series with...
  10. duke37

    Can someone please explain this circuit for me?

    My word, that is complicated, you would be better using an LM317T or similar. There is a string of Zener diodes to give a variable voltage between 4.7V and 10.7V. This is compared to the output voltage and if there is a difference, the output power transistors are driven to correct this. You...
  11. duke37

    DC Motors and speed control

    A resistor in series with a DC motor will reduce its speed, chose resistors to get the two speeds you want. You could look at a modified windscreen wiper motor which would give masses of torque at about the correct speed. A trip to the scrap yard is called for. I spent a lot of time repairing...
  12. duke37

    RC charging and discharging

    Your battery is upside down for the conventional way of drawing. Calculate the final voltage which will be two thirds of 6V. The equivalent feed resistance to the capacitor will be 100Ω and 200Ω in parallel. i.e. 66.6666666666666Ω From this calculate the time constant. For discharge the...
  13. duke37

    Phase shift oscillator help

    The circuitry of such oscillators is past my ability but - A3 is a standard inverting amplifier with a virtual earth. An ideal op amp works with the two inputs at the same voltage. The gain of the amplifier ensures that this is nearly true. The ideal op amp takes no current into its input...
  14. duke37

    Output Voltage Selector

    Mosfets contain an inherent diode which will conduct when the fet is used in the 'reverse' connection so the higher power supply will supply power to the lower supply. The way to stop this is to put a diode in series with the lower supply but this will give a voltage drop of about 0.6V, leaving...
  15. duke37

    Stepper Motor Sizing

    Unless your array was in existance since the beginning of time, there will be an acceleration phase. The torque required will probably be due to unbalanced mass and wind and snow loading loading, also bearing friction. You should measure these. At the rates you need, it would be better to run...
  16. duke37

    TORQUE DETERMINATION

    The torque generated will be that demanded by the fan, the motor should be designed to provide this with ease. The torque will be proportional to the square of the speed. The way to measure the toque is to mount the motor on a bearing so that the motor body can rotate, limit the rotation with...
  17. duke37

    Very Fine Cable?

    I have some very, very thin fibre covered wire. How much do you want? 0.1015mm (4 thou) E.D.R.C (Enammelled double rayon covered?) The fibre cover can easily be removed with a thumb nail. I have not tried to solder it yet. You are welcome to some. Trevor
  18. duke37

    2x 12 volt dc power supplies.

    Just connect the relay coil across the power supply. If you have a change-over relay you can make or disconnect a circuit as required. A relay of considerable switching capacity will be quite thirsty.
  19. duke37

    Can't identify if transistor is PNP or NPN?

    The connections of various transistor differ. Sometimes the collector is in the middle, sometimes at the end. You will need to look up the data or measure the transistor for gain. Note that just to confuse, some transistors of one type have a different connection layout, these may be labelled...
  20. duke37

    Coil problems...

    Modern wire will possibly have self fluxing wire so you could 'tin' the end of the wire or could use a candle to clear the insulation. Try to measure the resistance of an inch or so of the wire, that will tell you if you have a good connection. Some wires are double coated so a change in colour...
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