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  1. duke37

    Selecting the proper BJT and IGBT

    The pnp transistor puts a pulse of the right polarity to the output device. I have only used FETs and SCRs in this application so do not know about IGBTs. The load is not defined so that the output device can not be specified. I would be inclined to simulate this part of the circuit to see...
  2. duke37

    Car Immobilizer

    Car zappers are often run on a similar frequency to the 70cm amateur band and have negligible selectivity. A 10W transmitter nearby will stop the lock working.
  3. duke37

    dc genetators

    If this is a shunt wound generator, the field winding is powered from the output. If the output is shorted, there is no voltage to supply the field coil. This type of generator starts by utilising the remanent magnetic field, this is weak so too much of a load will not produce enough feedback.
  4. duke37

    AM receiver not working

    There is a 10uF capacitor across the battery, this is the one I would go for. Also have a battery with a low internal resistance (new). Motor boating is instability at low audio frequency so it is the large smoothing electrolytics which need to be good.
  5. duke37

    Selecting the proper BJT and IGBT

    Post the circuit diagram. Define the power supply, input signal and load.
  6. duke37

    rain warning device

    Shunhook I sent a private message with my phone number and e-mail address but have heard nothing. I certainly have enough posts to send a PM, look top right to see if there is one to be read. Duke37
  7. duke37

    AM receiver not working

    Motor boating is usually due to bad power supply. Make sure that the by-pass capacitors are good and connected correctly.
  8. duke37

    troubleshooting dc electrical machines

    It might also be due to an open circuited winding. You could measure the resistance between segments or measure the resistance across the brushes. Usually, the faulty winding will be linked a burnt commutator segment.
  9. duke37

    Ohm's Law doesn't work - Weird?

    The maximum power outpuit is obtained when the source resistance equals the load resistance. When this is so, the source voltage will drop to half the open circuit voltage. You could use a potentiometer as a load and adjust it to give half voltage. Then the resistance of the potentiometer can be...
  10. duke37

    Ohm's Law doesn't work - Weird?

    The solar cell will have a resistance which must be taken into account. The batteries will have a low internal resistance.
  11. duke37

    How to trigger an EFI computer

    What is an EMM and what is an EFI computer? I would tend to keep away from the ignition coils since there could be large voltage spikes which would be difficult to handle.
  12. duke37

    100VDC bus & arcing connectors?

    There will be inductance in the cicuit, maybe a little, maybe a lot. This will have energy which will need to be dissipated by the power switch. A zener diode across the fet with a voltage lower than the fet's limiting voltage may do. It will need to be fat enough to take the energy without...
  13. duke37

    100VDC bus & arcing connectors?

    Making a DC contact should not be much of a problem. The contacts will be cold and will be approaching rapidly so the short arc will be quenched quickly. Breaking a DC contact is difficult since the arc will start as soon as the contacts separate by the smallest amount and will continue as the...
  14. duke37

    A 'trip' switch, looking for anwsers

    A DC motor with brushes has an armature with several coils. The minimum is three but there can be many more. The coils are connected to a commutator which the brushes rub on so the appropriate coils are connected to make the motor turn. The magnet (permanent or electro) is on the outside of the...
  15. duke37

    A 'trip' switch, looking for anwsers

    You need to be much more specific. 1. What is the power supply? 2. What is the resistance of the electromagnet? 3. How long should the magnet be energised? 4. What is the time between energising? 5. Should this automatically cycle on and off? 6. Any more useful information. I know...
  16. duke37

    Coils

    If you play with iron filings and a strong magnet, then you will have trouble. If you wish to do so, then place the magnet in a plasic bag and then when the experiment has ended, the magnet can be taken out of the bag, leaving the filings behind.
  17. duke37

    rain warning device

    The RNIB is the Royal National Institute for the Blind. I used to service the tape players but they do not need my help now that they have gone digital. If you are in the UK I could have a look at it for you. I am in mid derbyshire. I assume it could be easily posted. Send a private...
  18. duke37

    reparing Receiver - TX-8511

    The technique of electronics repair is knowing just where to hit it.:):)
  19. duke37

    Coils

    As I said before, you an fill the space with thick or thin wire. The power output will be similar. Thick wire will give a high current but low voltage. Thin wire will give a high voltage but low current. If you are going to use a bridge rectifier which will drop some voltage, then thin...
  20. duke37

    Voltage as potential difference - out of the box question

    I do not think that your two examples are different from each other, you are only cocerned with the voltage between the two points. If there is an insulator between the points then it will block the transmission of current until the oltage gets sufficient to pull electrons off the fixed...
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