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Type: Posts; User: betwixt

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  1. Closed: Re: how to select ac to dc adapter for a given device

    The voltage must match.
    The current rating of the adapter must be equal to or greater than the device. More means you have a safety margin.

    If the voltage and current ratings are sufficient, the...
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    Closed: Re: 820 1K - what does the 1K mean?

    I would guess those are alternative values, maybe for different tubes, for example instead of ECC83 it could be for E88CC which is a similar but more 'robust' type for rugged applications. That...
  3. Closed: Re: Need help/tips in fixing my Acer projector.

    I have no experience with these at all but the symptoms suggest either a power supply fault or something is overloading the power supply. The regular 'tick' is a characteristic of a PSU that is...
  4. Closed: Re: Changeover relay circuit standby power supply

    The coil is powered directly from the rectified AC so it de-activates as soon as the power fails. We have no idea what voltage comes from your transformer or what the relay coil is rated at so if...
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    Closed: Re: Elementary battery question

    The plug type is the choice of whoever designed the unit the battery is connected to, it isn't part of the battery itself. Almost certainly the red wire is the positive connection and the black one...
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    Closed: Re: Isolated Converter RS-422

    RS-422 should have high noise immunity already.
    If you can build yourself, UART->Opto->ADM488 or ADM489 would work and be simple. Keep the opto on the UART side where there is only one data line.
    ...
  7. Closed: Re: Changeover relay circuit standby power supply

    Connect the relay coil across the input side of the regulator, using a series resistor if the voltage is too high. Then, switch your output using the relay contacts between the regulator output and...
  8. Closed: Re: Mains leaking currents causing problems in my house

    No, I meant the one in the Belkin device in post #38.

    I understand your confusion over this, there are factors most people wouldn't think twice about but then most people have a grounded socket. ...
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    [SOLVED]Closed: Re: Wiring of DC fans in Series

    Q4 is needed if there are two fans in series. The circuit will try to maintain the center at ~15V but the dissipation would be a problem, especially under the circumstances I described in post #12.
    ...
  10. [SOLVED]Closed: Re: Generation of 4 Phase Shifted clock Signals

    If the frequency is fixed, and you are using logic levels which are precise, you can get 90 degrees shift with one resistor and one capacitor. Just use three inverters, one to invert your original...
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    [SOLVED]Closed: Re: Wiring of DC fans in Series

    You are missing the fan connections and 100R is far too low in value, the resistors alone would dissipate 2.25W each!

    What Klaus is suggesting is basically two emitter follower circuits, they...
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    [SOLVED]Closed: Re: Wiring of DC fans in Series

    Yes, you can use two 7815 regulators to drop the 30V down to two 15V supplies but the drawback is they will almost certainly run very hot. They have to dissipate (voltage dropped * fan current) Watts...
  13. Closed: Re: Mains leaking currents causing problems in my house

    I think the "not grounded" indicator is to warn you the protection isn't going to work. All 'surge protectors" and similar protection devices are filters and over-voltage traps that rely on a good...
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    [SOLVED]Closed: Re: Wiring of DC fans in Series

    Generally not a good idea but it depends on the actual fan design. Most low voltage DC fans do not draw a precise current and it quite likely goes up and down as the fan rotates. As a consequence,...
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    Closed: Re: Latched Relay Car Immobilzer

    You understood correctly, but in this application you DON'T want the diode to conduct so it is wired the other way around. It will still conduct when the power is removed because at that instant both...
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    Closed: Re: Latched Relay Car Immobilzer

    Almost, the diode is in the right place but the arrow should point upwards. As shown it will conduct when the switch is pressed and divert the current away from the coil, the intention is it DOESN'T...
  17. Closed: Re: Algorithm to estimate given battery chemistry and capacity

    Vehicle charges, even most mobile phone chargers, have a communication path to the battery management system. They can tell the requirements by asking the management system what it needs and adapt...
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    Closed: Re: power supply residual voltage

    Your claims don't seem reasonable. How could a residual voltage of '+/-25V' appear on a 12V output?
    Are you saying it went up to 37V or down to -13V and under those conditions how could your...
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    Closed: Re: ac consumption in a adapter

    Without knowing the exact specification of the power adapters nobody can tell you exactly.

    A GUESS would be:
    100 adapters at 6W each = 600W DC load

    If the adapters use conventional...
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    Closed: Re: Latched Relay Car Immobilzer

    That is correct.
    With no power applied, there is no path to power the relay coil. When the switch is pressed, power reaches the coil and the contacts close. From then on, until the power is removed,...
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    Closed: Re: how to change pir sensor coverage angle?

    I wouldn't 'tweak' a commercial product, I would start from scratch.

    I assume this is just a one-off project and not for mass marketing so I would suggest you get hold of an old scrapped TV or VCR...
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    Closed: Re: Latched Relay Car Immobilzer

    You almost have it right. the relay contacts on the left go across the momentary switch instead of chassis. Basically, it makes it think the momentary switch is being held closed. Wired as shown the...
  23. Closed: Re: Will the TVS diode protect the DC line from AC power?

    The TVS will protect against excessive voltage provided the current is limited to a suitably small amount but it will not protect against the polarity reversing. For example, if the TVS clamps to...
  24. Closed: Re: Protecting the inputs of HV7802 current monitor from damage due to inrush current

    I think that should be 100uV not uA Klaus ..... but we know what you mean :-D

    Brian.
  25. Closed: Re: Mains leaking currents causing problems in my house

    Beware, most 'plug testers' work by looking at the difference between the three pins, live, neutral and earth. As you only have two pins it may not work.

    There is an alternative that would make...
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