Type: Posts; User: BradtheRad

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  1. Closed: Re: Howcome 3 phase 6 pulse rectifier fed loads dont need PFC

    After rectifying AC supplies to DC...
    A capacitive load (or capacitor filter) causes supply Ampere waveforms to get out of alignment with supply voltage waveforms (characteristic of power factor...
  2. Closed: Re: Voltage input to BLDC inverters on tethered drone?

    56kg is 123 lbs US. Is a manned craft in the works? Experimenters have done this and put up Youtube videos. Some appear genuine as their homemade drone lifts them in the air.

    Example, electric...
  3. Replies

    Closed: Re: NIMH Button cell 8.4volt 40mA

    Your schematic appears to use capacitive drop to reduce current from house voltage, then to feed a simple DC power supply.

    Although your circuit may be suitable, it's taking a chance when we...
  4. Closed: Re: How to connect VFD to a laptop or computer?

    Is your software registered? Is your module registered? Getting success until the crucial moment, then a strange error message appearing might be their way of blocking unregistered software or...
  5. Closed: Re: Voltage input to BLDC inverters on tethered drone?

    12500W 800V works out to 15A. It seems reasonable considering lightweight lamp cord carries similar current levels. On the other hand if voltage were 400V then we're talking more than 30A which...
  6. Closed: Re: How to choose right PWM frequency for 3 phase ac motor

    There's the fundamental frequency and the carrier frequency. The carrier frequency is several times the fundamental. There's no particular formula. It depends on what's feasible for you to work with....
  7. Closed: Re: Freq computation without DIV instruction for 8bit MCU

    Consider creating a lookup table. Say you want two digits of precision... Then you need an array of 100 elements. Exponents are a simple matter of reversing the sign (positive to negative, negative...
  8. Replies

    Closed: Re: AC-DC power supply design

    Yes, although its specs should be chosen to suit your system. Ampere saturation rating needs to be much higher than 9A. This simulation is a simple power supply, comparing the effects with a choke...
  9. Replies

    Closed: Re: AC-DC power supply design

    Another possibility is a choke filter. This is useful for smoothing current spikes which are typical with capacitor filters. A choke might go on the AC side or it might go after the diode bridge (or...
  10. Closed: Re: L1 and C1 value for EMI filter design ?

    The capacitor Farad value can not be too high of course, lest it pass too much current and destroy itself.
    Probably 1/10 Watt is reasonable. Calculate a Farad value associated with that amount of...
  11. Replies

    Closed: Re: AC-DC power supply design

    To illustrate here's a simple simulation of 2000uF charging through resistor and diode from 240 VAC source (peaks=340V). Timeframe 1 second.


    Looking at your schematic it could be done by...
  12. Closed: Re: Voltage input to BLDC inverters on tethered drone?

    This calculates to average 1A current draw, 400 ohms impedance (in round numbers). That amount has to be achieved by reactive impedance (coils with large Henry value), or ohmic resistance...
  13. Replies

    Closed: Re: AC-DC power supply design

    Suppose you pre-charge the capacitors directly from an auxiliary power supply? Install a plain diode and resistor, calculated so caps take a second or two to reach 90 percent running voltage. Power...
  14. Closed: Re: Testing Amps on rewound microwave transformer

    Yes, if your load doesn't change resistance in use. Incandescent lamps increase in resistance when they glow. Normally this throws off your calculation. However if you apply only 48V instead of house...
  15. Replies

    Closed: Re: BJT amplifier design

    Common base mode is suitable. It's tricky to adjust bias voltage and current, in order to find a good operating point.

    Simple simulation using your specs of Rin, Rout.
    Signal is applied at...
  16. Closed: Re: Voltage input to BLDC inverters on tethered drone?

    I wouldn't be surprised if the drone has its own step-down converter. High current is needed in R/C aircraft. 25 years ago electric planes typically had battery packs of 5 or 10 or even 20 'C' cells...
  17. Closed: Re: Voltage input to BLDC inverters on tethered drone?

    Tether wires appear lightweight and thin, implying low Amperes. I imagine it takes from 100 to 300 watts to lift a drone cam. And it seems convenient (as well as sensible marketing) to make the...
  18. Closed: Re: Testing Amps on rewound microwave transformer

    Simulation of transformer with various loads. Switches were closed in sequence. Scope trace travels to the left. Notice volt reading drops as current draw increases.

    A resistive type load is...
  19. Replies

    Closed: Re: Easiest way to get 5v and ~1V

    One diode pointing downward provides 0.6V regulated voltage. Two diodes yield 1.2V. (Similar principle to a zener diode.) A safety resistor is needed.

    If you want a specific reference voltage,...
  20. Closed: Re: Testing Amps on rewound microwave transformer

    One way is to attach various resistors and measure AC volts. That gives you an idea when the secondary output voltage starts to drop, thus letting you know how much power you can get from your...
  21. Closed: Re: Earth leakage Detection "positive" as well as "Negative" >30mA.

    Ordinary multimeters like I've used detect current as DC only.
    Here's a handy trick to measure AC current: Insert a resistor inline, and measure AC voltage across it. Resistor value should be very...
  22. [SOLVED]Closed: Re: Need very basic R-C "delay off" circuit

    Simple diode-resistor-capacitor networks create a gradual ramp-wave when you input a sudden transition.

    The principle behind the downward ramp (lefthand) is obvious.

    It's not as obvious how to...
  23. Replies

    Closed: Re: DC Booster for Solar Pump

    A voltage doubler can provide your step-up ratio, almost 2x.
    Two voltage doublers acting symmetrically provide AC to the load.

    Simulation using Nakagome type.


    Bias was adjusted to...
  24. [SOLVED]Closed: Re: Technique behind the Charging and Inverting Function of an Inverter

    I once put a voltmeter on the charger for my lawnmower battery. It read 10 or 11 VDC. Yet it was able to charge a 12V battery. I wondered how this was possible? It took me a while to figure out that...
  25. Closed: Re: Automatic Water Level Controller - Dynamic Dry-Run and OverLoad Current Calc Rela

    When starting up your motor is likely to draw several more Amperes than it does during normal running.
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