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  1. duke37

    smooth range variable transformer?

    The fan is AC driven and Poor Mystics syggestion of a triac controller may be the way to go. However, the motor is a capacitor run type and my not like a distorted waveform. Contact the suppliers to get their recommendation as to how they control the speed. Switched series resistors would...
  2. duke37

    DC input insted of rectifier?

    No, there is a negative line supplied by a voltage doubler through C2. Capacitors will not pass DC. Incidentally, what does the gubbins do?
  3. duke37

    Solar Attic Vent Question

    Here is a simple circuit that could work. You will need a light dependent resistor, the ORP12 has been around for many years and is still sold. The 4093 is of the CMOS family. The resistor should be set so that the voltage across the resistor is about 6V at an intermediate light level. There...
  4. duke37

    556 timer circuit with a problem

    You could pull the 0.1 caps, one at a time and see if the problem is still there. You can trigger the 556 by hand with the caps out. Try to simplify the problem by getting one part working at a time.
  5. duke37

    556 timer circuit with a problem

    I attach a diagram of what might do your job, I show only half the circuit, the other half is identical. The input is by-passed with a capacitor to reduce the possibility of noise input. The untriggerd input is tied down to ground with a resistor. Have you tried this on your circuit? The two...
  6. duke37

    Induction Motor Switch-off Transients

    Heathkit used to supply transformers which were a little light on the iron. On switch-on there was a thump on the iron cabinet due to the escaping magnetic field when the transformer saturated. On the principle that action and reaction are equal and opposite, there is quite a force on the wire...
  7. duke37

    Induction Motor Switch-off Transients

    When the core goes into saturation, the input current is limited only by the primary resistance which should be low for an efficient transformer. The high current then heats the wire and perhaps spoils the insulation between turns. Transformers can go into saturation during switch-on and I have...
  8. duke37

    556 timer circuit with a problem

    A 10A fuse seems to be a bit irrelevant, nothing in the circuit could stand that. The 4069 is an invertor which changes output when the input crosses about half supply voltage. If there is noise on the input signal then you can get multiple output pulses. The 4093 is a Schmitt trigger which...
  9. duke37

    Induction Motor Switch-off Transients

    Toroidal transformers have one thin lamination with aligned crystal structure. This makes them more efficient but means they run into saturation more abruptly. Is it possible that the saturation voltage can be obtained? Can the transient votages be measured when the motor is switched?
  10. duke37

    556 timer circuit with a problem

    The relay coils will take quite a large current and even a 47uF cap is unlikely to bypass a spike. The 4049 will take very little current and a resistor 1k to 10k in its supply should be OK and will supress any spike in association with a bypass capacitor to that particular chip. I do not...
  11. duke37

    556 timer circuit with a problem

    The trigger input will sit at 12V due to the 10k pull-up resistor. The pulse coming in from the 4069 will have a positive going edge and a negative going edge. On the negative edge, the trigger input will go low and then will rise to 12v as the capacitor charges. On a positive going edge, the...
  12. duke37

    dc-dc step up circuits in series?

    Probably not. If it is a step up convertor using an inductor, then the output and input will have a common ground (earth) and stacking two outputs will short the power supply. If the inductor is in reality a transformer with the output isolated from the input (unlikely) then it should be...
  13. duke37

    op amp (filter)

    It will be necessary to use one of poor mystic's rectifier and output for each filter output. Better to start wih one and perhaps work up from there if required. Poor mystic, what do you think about eliminating the zener and placing another led in the emitter of the BC348? Would this do the...
  14. duke37

    12v to 220v inverter design

    It appears that the transformer is wrong. What transformer are you using? Is it a 12V transformer used in reverse? If you get a 220V to 12V transformer, there will be extra turns on the secondary to compensate for resistive loss when under load. The turns ratio may be 10% out. If this...
  15. duke37

    op amp (filter)

    The rail voltage should go to the + input and the - input should have a connection to the output to bring the two inputs close to one another. See A on diagram. I have included a capacitor in the input since I do not know what the input signal is like. B on diagram shows a unity gain two pole...
  16. duke37

    op amp (filter)

    Poor mystic I wondered about the DC conditions of the first amp. I would put a fat capacitor on the input and a high value resistor to the centre reference point to set the mean running voltage. The 5k6 resistor should go across the 1u cap to set the DC negative feedback. I have never used a...
  17. duke37

    Single supply 5V LM324 Half-Wave Rectifier

    The amp can only give an output of 3.5V (supply -1.5V) The diode will take 0.7V, giving a maximum output voltage of 2.8V. Your resistor is referenced to 1.5V not ground so the maximum across the resistor is 1.3V. Seems it should work. Is this right Steve?
  18. duke37

    Controlling My Office Water Heater

    Under no circumstances put a diode across the AC relay, if you look, you will see that it is directly across the mains. If you are lucky, a fuse will blow, if you are unlucky, the exploding diode will hurt you. AC relays have a copper shorted turn over part of the pole piece to limit the back...
  19. duke37

    op amp (filter)

    Look up Wikipedia, "state variable filter". This filter gives low pass, band pass (mid range) and high pass outputs. Is the first op-amp correct in poor mystics circuit?
  20. duke37

    how to charge those capacitors please ?

    Capacitors such as you have can provide many tens of amps depending on the external resistance. Electric fencers are rated on energy and the most powerful ones hold about 1 Joule, your capacitors can hold 6.5J. Blunderbusses were more dangerous for the firers than for those they were fired at...
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