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Thread: Relay Voltage question

  1. #11
    Variable Bitrate
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    self induction happens when you cut the steering power from relay.
    the magnetic field falls down and induct a voltage back to steering part.
    can destroy yICs, if you don't terminate this selt induction.

    thats why the question where do you get this low voltage.

  2. #12
    Variable Bitrate camo.b's Avatar
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    One thing i was thinking of was a mute wire on a parrot bluetooth kit...i believe its 3v when its telling the "radio' to mute and a ground otherwise.

  3. #13
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    thinking, believing or known?

    does it mean you want mute the radio with this signal?
    do you know which signal needs the radio for mute mode?

  4. #14
    Variable Bitrate camo.b's Avatar
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    I know the parrot outputs a +3v when muting a sterio..i want to use this as a input for a mjs usb in/out or a joycon...either way i want the carpc to pause the current media when i recieve a phone call.however its done i need a alt-D (keystroke)to be issued upon 3v from the parrot...just need to be able to operate a relay from that voltage. Any thoughts?

  5. #15
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    i think you don't need a relay. this should work with few ampere. so you can use a transistor.
    may be you can connect the signal directly to com-port. but i don't know it.

  6. #16
    Variable Bitrate camo.b's Avatar
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    I was thinking transistor a while back.ill keep looking into it.

  7. #17
    Raw Wave
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    An whilst pennies drop, the harryberlin's relay problem is solved with the usual spike protection diode (1N4007 or 1N4004).

  8. #18
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    yes you're right, you can fix the problem with a diode.
    but i think the better way is to use transistors.
    or may be a small reed relay. but not such a big thing.

    ...
    Last edited by harryberlin; 02-02-2014 at 08:22 AM.

  9. #19
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    Transistors are not a better way to prevent relay spikes - ie, quenching the spike.

    I don't see what relevance a dc-dc or dc-ac converter has - we are not 'converting' the low voltage output.

    If talking about a transistor for a buffer for the relay coil etc you'd probably use an NPN transistor as on Open Collector output which could ground a 12V relay, or the load direct (if a few Amps), or control a MOSFET or other transistors.

  10. #20
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    I still don't see what relevance it has here - we are not 'converting' voltages nor providing a power supply/voltage. And the OP should have the call if bantering is welcome.

    camo.b's 1.8V or higher output voltage turns on a transistor. That transistor can ground a relay coil, or another transistor. The output else its transistor could also control a MOSFET that can switch loads up to 50A and higher ($2, 100A).
    Not that the OP Champak has yet specified a minimum voltage, but I suspect it'll be above 1.8V - maybe 3.6V etc.

    If switching a relay coil, a reverse biased diode (1N4004 or 1N4007) can be placed across the transistor's Collector & GND, or as is often done, across the relay's 86 & 85 where 85 is the more -v, ie, GND. The Cathode/line end of the 1N4004 or 4007 diode goes towards the more +ve ie, Collector or relay 86. IOW the NON-line end to the transistor's Emitter or relay 85 which should both be GND in this case.
    A 1N4004/4007 diode is the most common solution for relay coil 'self induction', ie the huge -ve voltage spike released by a coil when switched off. (Place your fingers across a non-spike protected relay coil when de-energisied if you don't believe me.)
    The diode spike-suppression solution is ironically the cheapest as well as the best implementation (for common relay applications and electronics).

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