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  1. duke37

    High voltage, low current transformer

    Please give a bit more information. What is the input voltage, is it unchanging up to 12V or does it need to cater for varying voltage? Is the input AC or DC.? Small relative to what? Is the output AC or DC? Does it need to be stable? Some information on the application would be helpful.
  2. duke37

    simple 24V DC brushed motor driver circuit with relays help

    Why DC? Consider using a washing machine universal motor running on AC. Control it with a dimmer control. this may need amplifying to supply the current. The drum assembly may also be useful.
  3. duke37

    Car Parking Sensors Help Needed

    One possibility is to put a microphone close to the sensor speaker and trigger a crude oscillator running at a lower frequency. The sensor speaker may be too small to output a lower frequency so another speaker would be necessary. This option would mean that there would be no interference with...
  4. duke37

    Hot Wire Cutter Power Supply

    I attach some photos of the lamp protected dimmer. The transformer is 24V and the length of the wire is 1m. I also show a series lamp which can be used to slowly power old valve radios or devices which have a tendency to blow fuses on switch on. If the lamp is broken, then there will be...
  5. duke37

    Adding to existing circuit

    I do not know where this array will be connected. Without extra power, it is unlikely to work. The base of each transistor should have a current limiting resistor. Depending on the load it could be 1k to 10k. Each led should retain its current limiting resistor.
  6. duke37

    Hot Wire Cutter Power Supply

    The cold wire resistance will be less than the hot resistance so you will need to measure both voltage and current. A longer wire will need more voltage but not more current. AC or DC will do the same job, I would not modify the charger. There is likely to be a bridge rectifier in the...
  7. duke37

    Hot Wire Cutter Power Supply

    I helped my neighbour make one a short time ago and I have arranged to photograph it tomorrow. The danger is that any works with mains voltages has to be done properly. If you use a Variac, then you should also use the battery charger or another transformer to provide isolation. The core...
  8. duke37

    Adding to existing circuit

    There are two possibilities. 1. The power supply or cable can not provide the current necessary. 2. The new circuit uses two leds in series. If the voltage drops there may not be enough to turn them on.
  9. duke37

    TURNS PER VOLT of a transformer winding

    Where does the formula come from? What units does it use? How do you get 18 sq cm from the numbers you supply? 2 TPV seems to be reasonable for a large 50 Hz transformer.
  10. duke37

    Hot Wire Cutter Power Supply

    The battery charger has a nice looking transformer inside. The dimmer looks to be a triac controlled supply but I cannot see the triac. Using a triac into a transformer can give problems if the waveform is not symmetrical, this can give saturation of the core and big pop. This can be...
  11. duke37

    Quick question about equal input voltages for op amp?

    Even I am not quite perfect. :D
  12. duke37

    Simple LED Circuit help.

    The circuit drawing and design could be improved. It is convention that the positive is at the top, then the conducting diodes point downwards. The leds should not be connected in parallel, you should use a separate resistor for each led. The breadboard has a conncting bus down each...
  13. duke37

    Quick question about equal input voltages for op amp?

    The op amp will have a very small offset between its inputs (look up the data sheet) which with the very high gain, will drive the output as high or as low as possible, depending on the offset. Some op amps have two extra pins so that the offset can be adjusted to very, very small values but...
  14. duke37

    Off - On - Off timed circuit.

    You have a 1k resistance in series with the relay coil. This will limit the current. What voltage and current is needed by the relay?
  15. duke37

    Need help with a PSU schematic

    Its me again Kris ! I have simulated a half wave version with a 1M resistor across the 47uF capacitor. uA thus means voltage. I can get down to 200R load before the voltage goes negative, then it is limited to about 1.5V i.e. 2 diode voltage drops. It seems to me that the diodes across the...
  16. duke37

    running 230 V/50 Hz CLOCK in US?

    I tryed to find how the clock works but without sucess. There are three methods that I know. 1. Clock runs with reference to a crystal oscillator. 2. Clock uses the mains frequency as a reference. This very accurate in the UK and if the frequency does drift, then it is compensated to correct...
  17. duke37

    How To Determine The Resistance Of A Coil

    I assume that the solenoid runs on AC. The impedance of the coil will be the square root of the sum of the resistance squared plus the reactance squared. The resistance can normally be measured with a normal meter but I have a digital meter which does not like inductance so I use an analog...
  18. duke37

    Need help with a PSU schematic

    This is similar to my simulation but much neater. Differences 1. I used 50Hz not 60Hz 2. I put 10R in the transformer secondary, not 0R2. 3. I loaded the low voltage with 100R, not 48R. 4. I loaded the high voltage with 2000R not 612R 5. I Used two 470uF caps on the low voltage output...
  19. duke37

    Too much battery

    If you have a power supply to go into the 12V input port, you can determine the polarity. Alternatively, find the users manual or contact the makers. Is the battery pack inside the camera? Does the camera have two inputs? How about a sketch of the bits you have and how they are connected?
  20. duke37

    Too much battery

    Older equipment often had central pin negative. It is now more common to have the central pin positive. There is often a little diagram on the equipment to show the correct connection, you may need a magnifying glass to see this. Did you check the 'official' power supply for polarity?
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