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  1. duke37

    Egg Incubator Turner Motor Circuit :::: Need Help PLEASE

    Have patience, it takes me longer than that to put my brain into gear. Four hours is far too long for a 555 and 15 sec is marginal. You will need two timers, one for each time. I do not think that great accuracy is required for this application. Some people would use a microcomputer for...
  2. duke37

    Lights activted by reed switch

    Mosfet I would use a IRF540 since I have some. This has a resistance of less than 0.1 ohm when turned on properly. Power dissipation = I * I * R = 3 * 3 * 0.1 = less than 1W so it should be possible to run without a heat sink. There are many N channel mosfets which could be used, look for...
  3. duke37

    Lights activted by reed switch

    Would this do? A suitable fet could take several amps.
  4. duke37

    Lights activted by reed switch

    You must have the led polarity correct. You are feeding the circuit with the neg power supply output. With the led arrow pointing down, you need positive at the top. A transistor to invert the signal, taking very little current, could drive a mosfet to switch the leds. This would replace the...
  5. duke37

    How to re-wire an old AC drill to a new switch

    This is lmost certainly a series wound (universal) motor. In order to change direction, the wires to the field winding or the brushes must be reversed. A relay could do this. A lamp dimmer could be used to vary the speed but may be jerky at low speeds. Some of the wires may be to...
  6. duke37

    out of my depth!

    I think there is some confusion here! The alternator has its own regulator and produces between 13.8 and 14.4 volts. It will do this above tickover and on commercial vehicles at tickover also. The regulator for the gauges is to give a correct reading if the battery is not being charged...
  7. duke37

    Powering 8 x Kemo 12w Amplifier Modules?

    I could not get at the data sheets again. If I was right previously, the amplifiers want less than 10V. They may have a very short but happy life if run on 12V particularly if the supply is not stabilised and the output is high on low loads.
  8. duke37

    current flow

    To understand the cicuit and to simplify it, then neglect the very small current going into the 741 inputs. If you do not like this, then change to a fet input op-amp which will have much less input current. The - input of the 741 will be at ground potential, it is a virtual earth point. R1...
  9. duke37

    current flow

    R3 has to be pulled negative, the 741 gets the current from V2 to do this.
  10. duke37

    why do we use average power for capacitor?

    I do not follow your first post. Energy is measured in joules. Watts are a measurement of power. The power you can get from a capacitor depends on how quickly you can charge it and discharge it. Switch mode power supplies use high frequencies to get high power throughput. You cannot extract...
  11. duke37

    Powering 8 x Kemo 12w Amplifier Modules?

    I suggest you extract the relevant data from the data sheets. For instance, the amplifier has a maximum voltage supply of 10V. If you have eight amplifiers taking 800mA each, that makes 6.4A. A 2.2A supply may work if you keep the volume down or it may fry, why risk it?
  12. duke37

    Help with transformer. Large surge currents

    There are all sorts of transformers, high frequency inverter, 100V line sound output etc If it were a mains transformer I would expect the primary to have a resistance approaching 100 ohm. If it is a mains transformer or audio transformer it will have a laminated silicon-iron core. If it is...
  13. duke37

    Varying a high current low voltage power supply cheaply

    Where does the power come from? What does the power go to? Phase angle control of AC input could be used but may run into transformer saturation problems. You could put a bridge rectifier in series with an AC supply. When this is shorted across, it will drop little volage. A controlled...
  14. duke37

    Help with replacing component on circuit board

    If you are sure that the amplifier is faulty, then the best way of removing it is to snip the leads with a side cutter and remove each wire separately. Use a solder sucker to get rid of most of the solder and braid to remove the rest. The heat sink paste does not glue surfaces together, the...
  15. duke37

    Help with siren circuit

    Old electronic organs used a phase shift oscillator to generate low frequencies for vibrato. These ran at about 1Hz. Larger capacitors would give lower frequencies I could look up the circuit if you wish.
  16. duke37

    Help with transformer. Large surge currents

    If your 2A power supply is DC, no wonder it overheated. Transformers work on AC and the right frequency for the transformer must be used. The highest voltage winding may be the one with the highest resistance but this is not always true. Putting 5V AC into one winding and measuring the...
  17. duke37

    Identifying 3 unkown components

    270pF,100pF,1500pf and 51pF capacitors. Someone will be able to say what the second number is, I suspect voltage. The third line may be dielectric or tolerance.
  18. duke37

    Switch design with MOSFETs

    Megohm resistors are OK. Just make sure that the FETs can stand 24V on their gates with some leeway.
  19. duke37

    What is this part an where can I get it?

    Seems strange, 4.7uF is a standard value. An aluminium electrolytic may do. Replace the correct way round.
  20. duke37

    Gilbert Cell

    The bias to Q1 to Q4 is suspect. The base voltage is not well defined. You have used unbalanced inputs and the output looks like a simple switching mixer with no attenuation of the input signals. I think one of the inputs should be much more than 10mV. I have not looked at the waveform of a...
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