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  1. duke37

    differential op amp to measure current

    You can get a transformer from a dead computer power supply at no cost. You appear to want to change supply when the 50kHz supply fails so you do not need to measure it, just detect whether it is there. Use the recitified current transformer output to drive a changeover relay. Do you want...
  2. duke37

    differential op amp to measure current

    You could put a diddy current transformer before the bridge rectifier. This would give isolation and would drop less voltage than a sense resistor. The output of the current transformer will need to have a resistive load and a smoothing capacitor.
  3. duke37

    12v to 440v step up

    The voltage that you get from rectifying a sine wave into a capacitor is Vrms* 1.414 which is what Miguel has calculated. Some inverters (the simpler ones) give out a square wave where the Vrms, Vmean and Vpeak are all the same so you will get no higher voltage on rectification. Will this...
  4. duke37

    12v to 440v step up

    Or an inverter followed by a voltage doubler consisting of a capacitor connected to the junction of two rectifiers and then a reservoir capacitor. Or build your own inverter using an old TV line output transformer core.
  5. duke37

    For what value of L, will this circuit resonate at 332kHz?

    I have had a go with 5spice. The first tuned circuit seems to do the business, the second is damped out of existance. The second inductance is wierd! The terminating impedances are important. The 15pF has a large effect on the frequency.
  6. duke37

    For what value of L, will this circuit resonate at 332kHz?

    This is a pair of tuned circuits, top and bottom coupled. The tuned circuits differ one from the other so the terminating impedances will be different. I would tackle this by calculating an approximate value of inductance and then simulating the circuit, using various values of inductance and...
  7. duke37

    Understanding Mosfet modules (parallel and series diode)

    This is getting well outside my knowledge. If you are switching a tuned circuit it is possible to get a reverse voltage due to overswing. A series diode will stop reverse current. You could of course use a valve (tube) which will not conduct in reverse.:)
  8. duke37

    Understanding Mosfet modules (parallel and series diode)

    As I understand, the intrinsic diode in the fet is not very good so a fast or low voltage drop diode may be connected across the fet to help. The circuit you show seems to be a resonant circuit which could produce reverse voltages across the fet.
  9. duke37

    Bracket for Pluggable transformer ????

    If you do not want to use baked bean tins, you could make a saddle from aluminium strip. Once you have the dimensions right you could make copies in under five minutes. One problem is that most sockets are twins and you will be compromising its butty. An elderly person can be very...
  10. duke37

    SCR dropping voltage

    Still no ground connection. The gates will be leaping up and down relative to one another at the full mains voltage. How will the microcontroller cope with this?
  11. duke37

    Innovation Projects

    How about a wrist watch type of device which vibrates when it receives sound, the the deaf person can look for the sound source and lip read if it is someone trying to speak to them.
  12. duke37

    For what value of L, will this circuit resonate at 332kHz?

    You need to post the entire circuit, you have components going nowhere. It looks as if it might be a pair of tuned circuits, top coupled by the 15pF capacitor. F= 1/(2*pi*(L*C)^0.5)), I presume you can rearrange this equation to get what you want, I would do it if I didn't feel so grumpy.:)
  13. duke37

    Bracket for Pluggable transformer ????

    The UK socket is retained in the wall with two screws. You could make a saddle from best quality baked bean tin and use the screws to retain the transformer. There may not be much improvement if the output cable is being yanked with vigour.
  14. duke37

    mosfet transistor for cordless drill

    The radioshack fet is a IRF510 in a TO220 package which they say is good for 60V and 3A. The IRF640 to IRF645 would do about 15A. There are many others. The diode could cause the problem if connected the wrong way round across the motor. It would then present a short circuit. When you...
  15. duke37

    mosfet transistor for cordless drill

    What package was the mosfet in and what were the replacements?
  16. duke37

    how to connect light indicator

    Power in, Fand G Heater on F and E The thermal overload has a wire going in and nothing comming out. Does the heater work?
  17. duke37

    noob question on current rating

    :) Just gently operating without effort. You can make the power supply as big as you can lift it!:)
  18. duke37

    noob question on current rating

    If you have a 12V 36W bulb, then the current drawn on 12V will be 36/12 = 3 Amp. So a 5 amp thermostat and a 5amp power supply will be just loafing along. A 12V battery will be good but consider putting it on contiuous charge with a proper regulated charger, then you will have safety if the...
  19. duke37

    SCR dropping voltage

    The normal method to trigger a SCR with a floating cathode is to use a pulse transformer with the secondary connected to cathode and gate. You must get the polarity right, positive gate to trigger on. A triac will switch the supply in both directions with a trigger in either direction.
  20. duke37

    noob question on current rating

    The current drawn will be determined by the bulbs. The thermostat and power supply must be rated for more than this. Bulbs can run on AC or DC, perhaps your thermostat can also. For bulb long life, you could run them on a slightly lower voltage or put a small resistor in series to drop...
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