Search results

Search Forums New Posts
  1. duke37

    refrigerator causes power surge

    anyway, an easy way to find out if its a surge or a drop will be to plug an incandescent light bulb, right? Yes, that is good. Digital meters will show a range of numbers which will be impossible to interpret. Analog meters may well be too slow, however I have an old very cheap meter which has...
  2. duke37

    Come & get yer watts!!!

    To transmit power you need voltage and current, this will be determined by the load. A small motor may need 12V and 1A, a big motor may need 400V and 200A, a light emitting diode may need a controlled current of 10mA at about 3V. Audio amplifiers are normally made to amplify voltage and supply...
  3. duke37

    refrigerator causes power surge

    I doubt if it is a power surge. Most likely it is a power deficit. The fridge will take a large current to start and the voltage will drop. You may have a power feed which has too high an impedance. Is the power stable in your neighbours property? Are the cables in your house up to regulation size?
  4. duke37

    Transistor radio speaker

    Colin, I refer you to Mullard Reference Manual of Transistor circuits. Here they seem to prefer 3.5Ω with transformer or 35Ω speakers with no transformer and one case of 75Ω. They give a table of turns ratio for an amplifier using a pair of OC72s on 4.5V. Speaker Turns ratio 3Ω...
  5. duke37

    Transistor radio speaker

    Speaker impedance is not too critical so I suspect a fault somewhere. If the set has an output transformer, it possibly had a 4Ω speaker and if it did not have a transformer, it could have been 32Ω.
  6. duke37

    regulating transistor mosfet

    Electric fencer units used for keeping cattle in seems to be the way to go. You can buy these for a reasonable amount. 10kV is perhaps too high a voltage, 5kV should be adequate. The energy in the pulse should not exceed 1J for safety. The voltage needs to generated relative to earth. It is...
  7. duke37

    Take your guess!

    The energy which the battery supplies comes from the energy stored in the electrodes. They will be consumed during use and maybe corrode when not in use. I do not think the specific electrolyte is not important.
  8. duke37

    Can I use a blender motor as a fan?

    #9 says that it already has speed control, this could be modified to suit the application. The torque needed for a fan is proportional to the square of the speed so the motor current should be low at low speed.
  9. duke37

    current flow?

    If you draw a circuit diagram with the positive line at the top and the negative at the bottom, then arrows pointing down (diodes, leds, transistors) will conduct and pass current either by electrons or holes. Arrows pointing upwards (Zener diodes or relay catch diodes or power supply diodes)...
  10. duke37

    Help with a flasher circuit with 555 Timer IC

    My old brain is not too good so I had to find a book to remind me of what pin3 is. I deduce that it is the output. The book also says that 4.5V is the minimum supply voltage for the 555. The voltage required by the leds is not specified. It would be better to use a higher voltage and place a...
  11. duke37

    Anyone know a simple circuit to make a signal generator using a crystal oscillator? (if possible)

    Dave "no you cannot you will damage the crystal" Why is this? They are often run with a small voltage across them and of course pass AC when operating. They can be damaged by excess AC when used in a powerful valve oscillator. Trevor
  12. duke37

    Bass Amplifier troubleshooting

    The amp will not work properly until you get the DC conditions right. It looks as if the reservoir capacitor is faulty or excess current is being drawn, if the latter, something will be getting hot. If you have a meter which will measure AC voltage and ignore DC, then you can measure the...
  13. duke37

    Bass Amplifier troubleshooting

    It looks as if the transformer is 44-0-44 V. 44 * sqrt(2) = 62 according to my slip stick. This is the peak value which should be obtained with no load and no diode drop. The centre tap must be connected to earth/ground/common. A faulty reservoir capacitor will not hold the peak so the...
  14. duke37

    3 way/4 way switch

    I do not know what you are after, but 1V will not light a led and will have even less chance with two in series.
  15. duke37

    Beginners multimeter quest.

    I would go with (*steve*) and get a cheap digital meter, $10 should be plenty. The ability to measure transistor gain and capacitance is useful. Find out what the meter does. I have one with an input resistance of 1MΩ, this consumes 1W at 1000V, there is nothing in the meter to dissipate 1W so...
  16. duke37

    idle: driving steppers closed-loop?

    When I were a lad, model control used potentiometers for feedback. One wire plus two for a common power supply. Selsyns can monitor position. Three wires each plus two for a common power supply. Used to synchronise aircraft engines! How do printers and scanners do it?
  17. duke37

    Turning an LED Off when voltage is applied

    CMOS will operate happily on 12V. The 40106 hex trigger will work here. If the polarity is wrong, you can change the load or use two gates in series then you get three leds/chip. It should be possible to run the leds directly (with resistor) from the 40106 if they do not take much current.
  18. duke37

    Anyone know a simple circuit to make a signal generator using a crystal oscillator? (if possible)

    A picture would tell us if they are crystals or crystal oscillators. If they are crystals putting a voltage across them will do nothing. You will need a very good scope to look at those frequencies, 24MHz and 29.5MHz. Probably there will be many circuits on the net. If the crystals are old...
  19. duke37

    Turning an LED Off when voltage is applied

    If you have a significant load, you could put a LED with resistor across the switch, When the switch is open there will be voltage for the LED but the load will have to supply the current.
  20. duke37

    Which transistor to choose for my regulators !!!

    If you have current, then you will have loss. Resistors and semiconductors will have significant loss and there will be some loss in capacitors also. No circuit will operate without any loss. The LM2678 will drop 12V (24V to 12V) with little loss, the input current will be less than the output...
Top