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  1. Replies
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    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...
  2. 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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    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...
  6. 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...
  12. 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...
  13. 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.
  14. 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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    Closed: Re: how to change pir sensor coverage angle?

    That is exactly the thing but it only has a range of 10m (about 30 feet) so you would need more than one to give the 50' length you need.
    With a little effort you could make one with the same or...
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    Closed: Re: Elementary battery question

    It is a standard 18650 Lithium Ion battery. There are many chargers for it if you search with that number. There are three wires, one will be a common connection to the battery negative and a...
  17. Closed: Re: FSK 1200baud discrete "modulators". What do you think?

    The problem is the frequencies are low compared to the data rate. A change to logic high or low is likely to result in partial cycles of the tone and hence all kinds of spurious other frequencies....
  18. Closed: Re: Input stage to 24W buckboost LED driver is high in component count.

    At such low current and with a surge limiter after it, do you really need a very low Rds FET? The difference between all that circuit and a simple silicon diode will be ~0.5V at most. I appreciate...
  19. Closed: Re: Input stage to 24W buckboost LED driver is high in component count.

    Thought:
    As the first stage is only to block reverse polarity, can't you replace it with a diode?
    If the second stage is only powering the comparator and the 5V is decided only by D51 and the Vbe...
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    Closed: Re: STM32 16bit wav player using Dac

    I'm not sure exactly what that does but I suspect the '=' shouldn't be there.
    I'm also not sure you should convert to signed at all, does the DAC accept signed numbers?

    Brian.
  21. Closed: Re: Simple dipole compared to a folded dipole in a 2.4 GHz Wifi Yagi Antenna

    I would use a much narrower boom, the capacitive effects of so much wood covering half the elements would seriously de-tune it. I have used brass rod as the boom before with good results. 6mm dia...
  22. Closed: Re: Lumens/Watt in LEDs when forward current is very low.?

    Intuitively I would say it continues down to zero almost linearly. I would guess the graph doesn't go lower simply because it is outside the scope of normal usage, just like car fuel usage is...
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    Closed: Re: Limit Current Maintain Voltage PSU output

    You are asking for contradictory requirements but what I think you want is a constant voltage power supply with an indication when the current has exceeded 150mA.
    You will have to start with a...
  24. Closed: Re: Mains leaking currents causing problems in my house

    It's a long story but basically, the cable carries on beyond my house to a three-phase motor on a waste treatment plant nearby. The cables used to be overhead but trees fell across the wires and...
  25. Closed: Re: Mains leaking currents causing problems in my house

    Neutral and Earth are usually bonded together but not at the socket, it is done back at the distribution transformer where both have a real 'planet Earth' ground. If you bond them at the socket and...
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