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  1. duke37

    Need help understanding 70.7 Volt Line Audio

    The term match or mismatch means very different things from RF match where the load at the end of a cable is the same as the cable impedance. To get maximum output power, the losd has to be equal to the source impedance. The electrical distribution system would be interesting if the load was...
  2. duke37

    Need help understanding 70.7 Volt Line Audio

    70.7 (US) or 100V (Europe) use an amplifier which can stand various loads. The output line has transformers to connect the speakers. The transformer ratio is chosen to give the correct volume out.The impedance shown to the amplifier will be high with only one small speaker and will be low when...
  3. duke37

    Newbie Q: Can I repair this Sunbeam heated throw?

    The firemen may not have electrical qualifications but they see fires started by electric blankets. They also supply smoke detectors. I do not have electrical qualifications but if I see a cable with damaged insulation I know it is not safe. My sister has been given a hot water bottle for a...
  4. duke37

    Newbie Q: Can I repair this Sunbeam heated throw?

    The local fire brigade will test electric blankets, they always say scrap them if they are a few years old. Electric coats and gloves are available which run on 12V, These should be fairly safe with the correct power supply. A relation put an electric blanket to warm a bed and put a foam pillow...
  5. duke37

    Looking for 60A 60V mosfet

    You can get mosfets with voltage capabilty in the hundreds so why use a specialised 30V transistor? You can only use two in series with extra circuitry and should only be necessary above 500V. If the mosfets are conducting all the time, have you got the base connected to the source properly or...
  6. duke37

    British Television?

    I knew a Post Office chap who was responsible for finding TVs with no licences. He went to collect a detector van and stopped on the top of the Pennines for a cob. He had a play with the detector and the only thing on the hill was a shepherd's hut. A walk to this remote hut found a shepherd with...
  7. duke37

    How to determine current

    Just connect your current meter set to a current range in ONE lead between the battery and the LED. Start with a high current range then drop it if necessary. The current will rise very rapidly as the volts rise.
  8. duke37

    Help with a 240v time delay relay setup

    I know the tank as a hydraulic accumulator. This has a sealed rubber bag inside a steel cylinder. They are used to pressurise central heating systems.
  9. duke37

    Help with a 240v time delay relay setup

    You did not say what the line is. I assume it is a water supply pipe. A pressure switch is unlikely to be man enough to switch your pump directly and a contactor is possibly used and can be controlled with another input. I would consider restricting the feed to the supply pipe and use a pessure...
  10. duke37

    DPDT relay lifespan.

    Keeping the coil warm in a damp environment should extend its life.
  11. duke37

    Power and potentiate multiple fans

    I see that you need to enhance the output of a radiator. A small amount of air blown over the surface, perhaps ducted, will have a considerable effect Each fan takes a miserly 0.17A so ten will take less rhan 2A. The charger you show can provide 5A so will have an easy time.
  12. duke37

    Power and potentiate multiple fans

    A resistor will need to disipate a lot of heat so reducing the advantage of the fans. Parallel conection is good but series connection is also possible. 10 fans in series will need 120V which could perhaps be obtained from the mains with a bridge rectifier, depending on your supply. A lamp...
  13. duke37

    Applying PWM to load while controlling its current

    Q1 is always turned off, it needs several volts on the gate to turn on. You could use a p-channel for Q1 A low pass filter is shown. Will this compete with the 555 output frequency and just give a smoothed output. I see no circuit to turn Q1 on and off quickly to minimise heating in the...
  14. duke37

    How to design a transistor circuit that controls low-power devices

    As a nit picker, I would like to see correct display of values. Amperes are shortened to A, not a. Kilo is k not K (that is temperature). Numbers after a decimal point should have a number before the point so that it not lost e.g. .67 should be shown as 0.67 Do not use commas in numbers...
  15. duke37

    Max Ratings L298N - V*A!=W?

    With a simple DC motor The voltage sets the speed. The current sets the torque. Adding an extra load will increase the current. Add a fuze.
  16. duke37

    Charging cap with three phase

    Unless youu have a very sophisticated meter, it will discharge the capacitor. To get a significant discharge time you will need a large electrolytic capacitor and a meter with 10M input resistance.
  17. duke37

    Light bulbs as dummy load for Stereo ?

    I go to Rich who saves me headlight bulbs with one broken filament.
  18. duke37

    Charging cap with three phase

    Draw out your circuit. Disconnect the bridge, Measure the resistance between the alternator outputs. Three readings. Measure the output voltage between the three alternator outputs when running. Three readings. Measure the resistance or voltage drop of each diode at both polarity. Twelve...
  19. duke37

    How to determine Neutral/Live from transformer output

    If you wind an auto transformer then neutral in = neutral out.
  20. duke37

    Charging cap with three phase

    Draw out your circuit. Three diodes will need a four wire drive. Six diodes in a bridge can operate without the common wire.
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