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  1. Audioguru

    Interfacing two powers

    Why are you using a TIP125 power darlington rated at 5000mA when the 5V LED it is driving is using only 7mA? An ordinary little PNP transistor (not a power transistor and not a darlington) like a 2N3906 will work fine. Why is the current in R2 five times more than the current in the LED?
  2. Audioguru

    Dynamo Motor Sparks Inside

    When I was a teenager I found a cheap motor like that and I put a propeller on it and made it into a fan. The motor sparked inside like yours. The sparks made so much radio and TV interference that the RF cops came to talk to me. They said many people around me complained of interference. When...
  3. Audioguru

    Any idea for this switch?

    In his other thread he has a 24VDC/2A solenoid that he wants to activate "for a fraction of a second". He probably does not know how long it takes for the solenoid to work so the timing will probably need to be adjustable. A 555 monostable driving a little power transistor will work.
  4. Audioguru

    Solenoid Help

    Cadmium is a deadly metal so Ni-Cad batteries have been banned in many countries. China still makes them. 25 years ago I used Ni-Cad batteries in wireless tele-conference microphone transmitters. Many got the "memory" problem and most ended up shorted but zapping with a high current temporarily...
  5. Audioguru

    Solenoid Help

    I think the cheap Chinese 9V battery is only 45mAh but the decimal point is so small it is hard to see. It does not say its chemistry (if it is rechargeable then it might be old fashioned Ni-Cad) and it does not say it is 8.4V (seven 1.2 cells). It might be old fashioned Super Heavy Duty carbon...
  6. Audioguru

    Solenoid Help

    Google and I know nothing about "Knup" batteries. An Energizer ordinary little 9V Ni-MH rechargeable battery is rated at 175mAh when its current is only 35mA and its voltage drops to 6V. At 175mA its voltage drops to 6V in about 20 minutes. Your 450mAh batteries are much larger.
  7. Audioguru

    100MHz Schmitt Oscillator

    8mHz is a very low frequency. 8MHz is a radio frequency. "m" is thousandth, "M" is Millions. A huge difference.
  8. Audioguru

    How do I run a dc motor slowly?

    When I saw your 8 RPM I wrongly thought about audio that is cycles per second and 8 RPS is pretty slow but doable for a motor with no load when powered from PWM.
  9. Audioguru

    Solenoid Help

    Seven (?) little 9V alkaline batteries in series produce 63V with no load. If the solenoid draws 2A of current at 24V then at 63V it will try to draw 5.25A that is almost 18 times higher than the little 9V batteries can drive. You need two 12V motorcycle batteries in series to drive that 24V...
  10. Audioguru

    Timer for a toy car

    The datasheet of an LM555 or NE555 shows that its minimum supply voltage is 4.5V. A Cmos 555 is an ICM7555, LMC555 or TLC555 has a minimum voltage of 1.5V or 2V but their output current is low. A transistor to switch the motor circuit on and off will drop the voltage. A Mosfet as a switch might...
  11. Audioguru

    Solenoid Help

    A little 9V alkaline battery falls flat on its face when it has a current more than about 0.3A. Then its voltage will have dropped to 6V in one hour.
  12. Audioguru

    PWM help

    If you measure the battery voltage when the heating element measures only 4.12V then it will show you if the battery can supply the high current without dropping its voltage. If the battery voltage is reasonable then measure the voltages of other parts of the circuit to see what is reducing the...
  13. Audioguru

    Cockroft-Walton Voltage multiplier

    The capacitors marked "681" are probably 680pF that is almost nothing.
  14. Audioguru

    Trying to go from 12v ac to 12v dc

    12.5VAC has a peak of 17.7V. When rectified the voltage is about 15.9VDC. When the engine in the car is running and is charging the battery then the voltage will be about 14V that is less than the 15.9V from the rectified AC so the maximum amplifier power will be reduced a little. Connect the...
  15. Audioguru

    PWM help

    I listed everything that reduces the voltage. The battery is #1 especially if it is a cheap Chinese no-name-brand thing bought on ebay.
  16. Audioguru

    PWM help

    Maybe your Mosfet is a cheap fake one from ebay? Did you read the datasheet of the 555? Its output can not go higher than 1.2V less than its power supply voltage which should be fine for a real IRFB3813 if the supply voltage stays above about 6V. The heater draws a much higher current when cold...
  17. Audioguru

    PWM help

    I suspect that since you did not say the battery voltage when the PWM circuit was bypassed and the battery was powering the heater directly, then the batteries, battery holder, switches and wiring are heating and throwing away most of the voltage charge. Measure the voltage at the heater when...
  18. Audioguru

    How do I run a dc motor slowly?

    A simple series resistor reduces the current and torque of a DC motor. But PWM delivers full power pulses and lots of torque while reducing the speed.
  19. Audioguru

    Consultation

    What is the part number of your 555? Maybe it is a LMC555, TLC555 or ICM7555 Cmos one. Did you remove C6 and the diode?
  20. Audioguru

    Need help determining what pins go where

    I went blind with cataracts. Now my eyes have new synthetic lenses in them and my vision is perfect. My old body nearly died with a heart attack. Now I am young again with the blocked heart arteries held open with stents in them. I think my brain is OK. No more booze nor Mary Wanna.
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