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  1. duke37

    Keyboard repair after spill

    Phosphoric acid is corrosive. Put a cupro-nickel coin in Coke and leave it for a while and see what happens.
  2. duke37

    Transistor help

    Try Wikipedia.
  3. duke37

    Resistance of 1 foot of Romex cable?

    If there is water in the cable, it is scrap. You cannot get it out. You could cut the cable in half and keep the good half, cut the bad part in half etc. Or you could make a pulse generator and use a fast scope to look at the time that the pulse gets to be reflected. Another way is to...
  4. duke37

    How to rectify ac to run a dc motor?

    What are the bits attached to the brushes? Normaly they slide in a metal sleeve and have a spring at the back to keep them at the right pressure against the armature. It looks like a permanent magnet motor with red and black for inputs as you have used. Does the green wire go to the case...
  5. duke37

    How to rectify ac to run a dc motor?

    That looks as if not too much damage has been done. Measure the voltage on the spare wire relative to each of the input wires. Is it connected to the body? A common light dimmer is not just a rheostat, it is a phase controlled triac. It may work but may give complications. Use a filament...
  6. duke37

    How to rectify ac to run a dc motor?

    You need to determine the type of motor, If it is a permanent magnet motor then there will be some external magnetic field and there will probably be some 'cogging' where the motor goes round in slight jerks when turned by hand. If it is a shunt motor, there will be a field winding which must...
  7. duke37

    How to rectify ac to run a dc motor?

    The figures seem to be right. The mean voltage of a rectified sine wave is Vrms*0.9. The volts, amps, power are consistent. I cannot help with the smoke.
  8. duke37

    Stepping up voltage

    Yes, shoot through is a term used where one transistor turns on before the other is fully turned off. This may not be a problem if the current is limited and it does not occur often. An invertor running at 100kHz with a 1microsecond overlap will have problems, one running at 10kHz with the same...
  9. duke37

    Stepping up voltage

    You will need to specify the power supply and the components. Fets will be better than npn transistors if they are being driven by logic circuits since they take little power to drive. They are also more efficient. You can look up H-bridge yourself if you wish. It is a circuit which can...
  10. duke37

    Stepping up voltage

    It should 'work' but it will depend on the component values as to what you get. R3 (1k) will limit the power and you may get out less than you put in.
  11. duke37

    CAPACITOR

    A capacitor will not allow a sudden change in VOLTAGE. Capacitors and inductors store energy so in order to increase the voltage on a capacitor you need to provide energy. In order to increase the current through an inductor you need to provide energy. This cannot be done instantly so...
  12. duke37

    Transformer VA

    P=I*I*R P1=0.3*0.3*R = 0.09R P2=0.4*0.4*R = 0.16R So going up from 0.3A to 0.4A will almost double the heating of the transformer. You may get away with this if, as *steve* says, you run for a short time and then let the transformer cool or you may be able to cool it with a fan.
  13. duke37

    Transformer VA

    Yes, 40 ohms load would load the transformer fully. The resistance of the transformer secondary will be much less than this so that the power lost in the winding will be low. A transformer will normally be designed so that the loss in the primary and secondary is equal. The primary resistance...
  14. duke37

    Op Amp and capacitors

    I know nothing about Bode plots so cannot help with your question. I was however interested in the circuit which I had not seen before. I simulated it with 5spice and it is a band pass filter in the audio range. Simple and effective. The 3dB points can be determined from the response curve.
  15. duke37

    Transformer VA

    P = I * V is the output power of the transformer and should be much more than the power lost in the windings. P = I * I * R is the power lost in the transformer winding where R is the winding resistance NOT the load resistance. Low resistances can be measured with various techniques. In a...
  16. duke37

    Transformer VA

    If you use a transformer backwards you get a low voltage out. You may only get 180 to 200V with a low power transformer. You should not exceed the rated current. The heating in the transformer = P = I * I * R where R is the resistance of the winding wire. This does not change with the voltage.
  17. duke37

    Power Supply with 12V and 10A or 5A

    Battery chargers for charging car batteries are normally capable of several amps. They do not plug into the wall but are made in a separate box, usually with an ammeter. I have a 10A one. Modern complex chargers often will not turn on unless correctly connected to a battery. You do not...
  18. duke37

    Power Supply with 12V and 10A or 5A

    You cannot get out more than what the components are rated at, at least, not for long. Can you borrow a simple battery charger of 5A, this will give the rectified output required. A car headlight bulb in series with the output will limit the current to a safe value and give an indication of...
  19. duke37

    Pulse Train Detection

    What do you mean by half light level? Are the pulses shorter or less high? The pulses are very short so you will need to charge a capacitor at a very high rate using an amplified diode. Show us a sketch of the waveform at full and half level. The op-amp circuit you show converts the input...
  20. duke37

    Transformer to build 12 volt battery charger

    I do not think that any filling will stop condesation unlass the box is hermetically sealed. You could change the desiccant regularly. You could keep the chargers in your house and connect to the boat with a multiway cable.
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