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  1. duke37

    Is there a circuit that can energize a coil on 110v, and to keep coil de energized on 220v.

    Can you use an AC relay that will only pull in above say 150V. If the relay is a bit too sensitive, then a series resistance could be used. A diddy DC relay could be used with a suitable supply added. They come in all sizes fromTO5 upwards. It will need to be a fair size to accommodate decent...
  2. duke37

    Project: build a 12/24v DC geny from 2 cycle engine

    A gas engine should not need a choke like a petrol engine. A diesel should start reliably if you can crank it fast enough. If the engine runs at 3000rpm, then you could perhaps couple directly. A dynamo may be satisfactory at lower speeds and may be powerful enough to start the engine but be...
  3. duke37

    American Electronic to Australian

    The motor runs on DC and is servo controlled for the correct speed so the input AC frequency should not matter. However the power transformer will be designed for 60Hz and will have a harder time on 50Hz. Check that it does not overheat. If you have choice of 120V or 110V, then go for the lower...
  4. duke37

    Getting antenna to radiate

    The circuit shows a 50Ω output (forget the LPF) and the transformer multiplies this by 16 to get a load more suitable (800Ω) to the 2N2222 collector. The transformer needs to be close coupled with low leakage inductance and low capacitance. This is normally achieved by winding on a toroid core...
  5. duke37

    Need audio preamp/buffer constant current (power) for bussing

    A virtual earth amplifier can have several inputs, each not affecting any other input. The amplifier has the feedback to the - input of the op-amp, (edit) [with the + input to earth].Input resistors should be sized to give the amplifier gain required. Output will be inverted.
  6. duke37

    dimmer circuit problem

    Perhaps you have a very eager triac. It is often recommended to place a resistor (10k?) from gate to ground to restrain it a bit. Check that the snubber circuit is not a short.
  7. duke37

    220V solder iron under 110V

    As Harald says, this assumes that the resistance stays constant. The power dissipated is V*V/R so if V is half, P = V/2 *V/2 /R = V*V/R/4 If a diode is used, then the voltage is applied for half the time so the average power is half. The iron is a 80W iron with a diode so dissipates 40W as...
  8. duke37

    220V solder iron under 110V

    A resistor run on half voltage will dissipate one quarter the power. A resistor in series with a diode (AC) will dissipate one half the power since it conducts half the time. I do not think that taking the diode out will give the same heat on half the voltage. This seems to be an 80W iron run...
  9. duke37

    solid state transformer

    I do not know what you mean by a solid state transformer. Please state the details of the input and output(s).
  10. duke37

    Calculating Power Loss

    I do not have video most of the time. You need to get a consistent set of data. 12V at 4A means the resistance is 3Ω, not 2Ω as previously assumed. P = 12*12/3 = 48W P = 4*4*3 = 48W everything is consistent with 12V, 4A, 3Ω and 48W
  11. duke37

    Calculating Power Loss

    You have a load of 2Ω. With 4A the power is I*I*R =32W and the voltage is 8V. With 12V the power is V*V/R = 144/2 = 72W and the current is 6A. Which voltage do you have?
  12. duke37

    Trouble with 555 flyback driver circuit

    The core of a LOPT is made of ferrite which is insulating or of very high resistance so it will be difficult to ground it. There may be a metal clamp which can be grounded.
  13. duke37

    Opamp for High Frequency Output - Need Help

    You could look up circuits for radio transmitters, these are usually tuned circuits with neutralised transistors. High frequency transistors will be required, fets seem to be the current fashion. 30V is quite lively and a transformer may be the way to go to run from a lower voltage.
  14. duke37

    Trouble with 555 flyback driver circuit

    I do not like lumps of ground floating in the air, in pratice they need to be connected together. I prefer a common rail, normally at the bottom of the diagram. In the case of a delicate circuit driving a circuit which takes high current pulses or produces high voltages, then the associated...
  15. duke37

    Wiring up 2 or more 220V axial fans

    The motors are probably simple induction motors and without load will run at a speed proportional to frequency. When driving a fan, things are more complicated since the fan torque is proportional to speed squared and the power is proportional to speed cubed. It would make an interesting...
  16. duke37

    Electromagnetic emission...

    What you are making is a transformer with a shorted turn and a poor core (no laminations) with very little coupling to the secondary. The speaker tries to keep all the magnetic field between the magnet pole pieces but some escapes. Do not put a speaker near to a CRT TV or you will see the stray...
  17. duke37

    Electromagnetic emission...

    Adding an AC coil to a magnet will vary the strength of the field Remove the magnet and there will be AC field only. This can be detected 1m away or more. The detection device is called a radio receiver. Medium wave radios often use what is called a loopstick antenna (US) which is a multiturn...
  18. duke37

    Beginning electronics, understanding whats actually happening

    I have answered this type of question several times. Here we go again. Make yourself a crystal set, this will teach you about tuned circuits, their Q and ways of getting energy and out. Repair electric and electronic equipment. This will teach you logic, sadly often lacking and enhance your...
  19. duke37

    Is there even a difference if i use a thyristor instead of a transistor? Also any improvements?

    If this is a game where a loop of wire is passed over a wiggly wire with the aim of not touching, then the loop and the wiggly wire need to have no conductive coating. Most copper wire is enamelled and the enamel would need to be removed. If this is done by heating, then the wire would be...
  20. duke37

    JVC Speaker getting power but not producing sound

    In #13 I suggested using an analog meter to measure the resistance.If you do have one of these, try flicking a 9V battery across each driver. You should get some crackles. The bass driver should be OK if it measures 5Ω. The mid range driver should also measure a similar value. The tweeter may be...
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