Search results

Search Forums New Posts
  1. duke37

    "Coughing" Polk Audio PSW202 subwoofer

    As long as the voltage rating is adequate, the change to 50V working will not improve things. The fault is likely to be bad capacitors, to check temporarily connect a similar capacitor across the doubtful one. If the fault disappears then you have found the bad capacitor. Do not change...
  2. duke37

    Strange symbols in Cct. Diags.

    Or a sketch.
  3. duke37

    Trigger a relay at certain voltage?

    1. You can get low voltage relays, there may be one to suit you. 2. A single transistor with a zener diode in the emitter lead will need more base voltage to turn it on. 3. An op-amp or comparator with hysteresis will do what you want and can be adjusted as required. You do not give details of...
  4. duke37

    What should I get for beginning electronics?

    You do not need much solder or flux if the surfaces are clean. Old components such as I often use need the leads rubbing to get off the oxide even if they look clean. A high temperature and short time is much better than a low temperature and fiddling around.
  5. duke37

    How do you verify your ohmeter works?

    Testing a diode does not give resistance. In the forward direction a silicon diode will drop 0.6 to 0.7V irrespective of the size of the diode and the current passed. Try measuring a diode on more than one resistance range and the deflection will be similar, giving vastly different ohms...
  6. duke37

    Powering an AC induction motor with a function generator and an audio amp.

    My suggestion was to run the motors in series direct from the mains without any other clobber except some relays to alter the connections. Each motor takes about 0.4A at full power but will take less at a lower votage. The maths are complicated but the torque is proportional to the speed...
  7. duke37

    Powering an AC induction motor with a function generator and an audio amp.

    You got Watts and Amps mixed up in #6. Going back to the original requirement, you could put two or three fans in series to slow them down.
  8. duke37

    Powering an AC induction motor with a function generator and an audio amp.

    18V, 40W = 2.2A 90V, 40W = 0.44A How do you get 8W, power (watts) = volts * amps
  9. duke37

    How do you verify your ohmeter works?

    If an analog meter will not show full deflection when the probes are shorted and the set zero twiddled, then the battery is likely to be not up to the job, try a new one.
  10. duke37

    Powering an AC induction motor with a function generator and an audio amp.

    You would need a transformer to boost the voltage. A big one is needed to run at low frequency. Shaded pole motors have a phase shift due to the shading, I do nor know what the effect of low frequency would be, possibly a very low torque. However, the torque reqiured by a fan goes down sharpley...
  11. duke37

    Scooter motor to power wood lathe

    For 0.5HP at 24V you need 15A, quite feasible, you may be able to get away without smoothing so would not need a whacking great big electrolytic. To change direction, a H bridge would be nice but a relay would be adequate since it will not be changed often. The problem will be to get into the...
  12. duke37

    Home amp fuse bown always

    If you have replaced a NPN transistor for a PNP and vice versa then they could be toast. To get some volts in without blowing the main fuse, then use a series lamp of about 40W in the mains lead. Then see if any components get warm. I cannot read the circuit diagram easily but if there is a fuse...
  13. duke37

    Scooter motor to power wood lathe

    The modern way of cotrolling lathe speed is by using a three phase motor and a variable frequency and voltage three phase supply, connected to the mains. Do you need an accurate speed conrtrol or would stepped pulleys do? You will need to get the motor specification to decide on the 24V power...
  14. duke37

    10k trimmer

    Is the input electrolytic and the output electrolytic the wrong way round?
  15. duke37

    Converting AC to DC motor

    There are drives (boxes) which can take in 12V DC and put out 110V AC to drive shavers, radios, TVs, central heater controls and other low power loads.. These are used when the mains fails. There are uninterruptable power supplies for computers which charge a battery and then replace the output...
  16. duke37

    Converting AC to DC motor

    The way to use your existing motor is to get or build a 12V DC to 110V AC drive. I expect that this would cost more than you wish to spend. You have not said what this motor is driving. If the load is about 3kW then 250A at 12V would be necessary. A car battery could give 30A for an hour or two.
  17. duke37

    Converting AC to DC motor

    A car starter motor is 12V DC and runs fairly slowly, I think they are series connected so speed will be determined by the load. They are not intended for long term use but you could try to replace the brushes with standard carbon ones. A car dynamo is 12V and you may still be able to find one...
  18. duke37

    Help with fence charger schematic

    The inductance should be connected in the connection to the fence, not to ground. This will impede the fast lightning strike and help to pass the energy through a surge arrestor (spark gap) to ground on the fence side. This site electricfence-online.co.uk shows how a coil can be supported by...
  19. duke37

    Pre-Scaling a squarewave. Output weird.

    The 'box' display is because the scan is running at the wrong speed. Thus on one scan, you get a square wave and the next you get another square wave offset between the first one. Set the scope to trigger on the blue waveform not the yellow one.
  20. duke37

    Help with fence charger schematic

    1. Energy is required to create a spark, this is wasted energy. 2. A spark gap across the output should be installed. This with an inductance of six turns spaced 10mm or so, 300mm diameter will give some lightning protection. The parallel spark gap will also limit the output voltage. 3. The...
Top