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  1. Arouse1973

    Solenoid Back EMF

    Yes I was going to do that, but I was at home when I wrote this and wanted peoples feedback initially. I'll do this and let you know. Cheers
  2. Arouse1973

    Solenoid Back EMF

    Now I don't know if I am on the right track but I think I might need to include a damping factor into the formula. L=20mH C= 400pF (not unrealistic value) Dp=R/2*L=600 Then the V= -L*di/dt (t=5*RC) = 208*10^3 Volts divide this by 600 = 346V. I was getting about 350V. Does this seem...
  3. Arouse1973

    Solenoid Back EMF

    Thanks Duke. I'll keep you posted if I come up with anything more accurate. Thanks Adam
  4. Arouse1973

    Solenoid Back EMF

    Yeah could be Kris I don't know. I think I am going to go with your approach, seems the most plausible. As you say there must be a loss somewhere. If I come up with a better solution I will let you know. Cheers Adam
  5. Arouse1973

    Solenoid Back EMF

    By hand with a wire. I am not using a mechanical switch. Thanks Adam
  6. Arouse1973

    Question on calculating resistance needed

    You will probably also need a heat sink. It's going to get pretty warm with 250mA through it. Dave can you explain what you mean by it will never see 250mA, I am curious. Do you mean with the 48R or any value of resistor. Thanks Adam
  7. Arouse1973

    optical slave trigger

    What's a hotshoe?
  8. Arouse1973

    Total noob cant make switch work

    I think you need to move the lower wire and the link to the top of the resistor over one space. Looks like the swich is shorted I.e they are on the same line. Have not used bread board for 25 years so might be wrong
  9. Arouse1973

    Total noob cant make switch work

    :)Yeah sorry dave, the blue was quite faint, missed that. I wish they would just put the link to the component in full. Gets me every time.
  10. Arouse1973

    Solenoid Back EMF

    Sorry you have confused me. Its got nothing to do with cars and there is no swich. Thanks Adam
  11. Arouse1973

    Can I use heat duct vent as ground for a radio?

    Um confused. What are you trying to do. Do you have a radio powered from the mains? If so then you must have an earth if the radio has a metal chassis. Or are you talking about a counter poise anntena using the earth as the second part as the other pole of your antenna.
  12. Arouse1973

    circuit calculation

    Turn on and off, what about a switch?
  13. Arouse1973

    Total noob cant make switch work

    If its a standard switch with three contacts. Connect the middle pin to one side of the battery and anyone of the other contacts. If this does not work can you send a picture of the switch. Adam
  14. Arouse1973

    Solenoid Back EMF

    Close Kris, your adout double what you actually get in real life. Any more ideas? Thanks Adam
  15. Arouse1973

    Solenoid Back EMF

    Yes Kris What I was after for a bit of fun was a formula forworking out the voltage spike from a real world inductor which takes into account the capacitance and resistance of the coil.
  16. Arouse1973

    voltage divider transistor biasing...

    Thanks for that Kris.
  17. Arouse1973

    voltage divider transistor biasing...

    Kris can you please supply me the formula for the input imedance I am very interested in this. Thanks Adam
  18. Arouse1973

    voltage divider transistor biasing...

    What about the input bandwidth? Any ideas on that?
  19. Arouse1973

    voltage divider transistor biasing...

    Effective mode is when the capacitor is so low that re is dominant
  20. Arouse1973

    voltage divider transistor biasing...

    Kris that is what we call in the UK the cut of frequency -3dB.
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