AC mains indicator via induction

Discussion in 'General Electronics Chat' started by technokid, Nov 29, 2014.

  1. technokid

    Thread Starter Member

    Nov 29, 2014
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    Looking for schematics / circuits as to how to power an AC l.e.d mains indicator via electromagnetic induction coil. I believe, it is a safer and better method than direct connection to the mains.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The only problem with a current detection method is a load has to be present for the indicator to switch on.
    Direct connection is often done with a small neon, the small enclosed appliance type are very cheap.
    Max.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You could use a mini mains transformer + rectifier bridge.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I recently needed a bright LED to indicate the presence of 240Vac ( deep Well pump). My local thrift stores sells retired cell phone chargers for $0.50. These are the SMPS kind that take in 100 to 250VAC and put out an isolated, regulated DC of 3.6 to 6V, depending on make. These will run a 20mA indicator LED with a suitable current-limiting resistor...
     
    Last edited: Nov 29, 2014
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Why is it safer and/or better than hooking up to mains? All manner of devices and appliances etc are hooked up to the mains all around the world all the time. Just do it in a safe and acceptable way. It does not need to be done unsafely.
     
  6. technokid

    Thread Starter Member

    Nov 29, 2014
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    Small neon or other methods using LEDs, some of which, just like the neon method, are connected directly to the mains, making the circuit dangerous, where as a coil rapped around, the mains cable and powering up the led(s) 101% safe. As to the load, the coil produces the required emf , the led along (if necessary) with its resistance in series to limit the current, represents the load.
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Magnetically isolated LED will be a lot safer to make and use than a LED running straight off mains through a cap and a few diodes and resistors.
    Besides that because of the safety issues transformer-less circuits such as a mains led indicator are a forbidden topic on this forum.
     
  8. technokid

    Thread Starter Member

    Nov 29, 2014
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    It is safer because there is no direct link to the mains. Some circuits use X-Caps, to reduce the voltage to a small fraction of the mains voltage to power up the led, nevertheless, they are still LIVE connected. Mind you, not all circuits can be configured this way, but to make it isolated, the number of components increases.
     
  9. technokid

    Thread Starter Member

    Nov 29, 2014
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    ......well, a coil rapped around a mains current carrying wire is a transformer. Hence, why, I asked for a coil powered circuit. This method as I explained, previously, is the safest method that can be used. I agree, x-caps are dangerous.
     
  10. technokid

    Thread Starter Member

    Nov 29, 2014
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    can you show us the configuration, the diagram.
     
  11. MikeML

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    Oct 2, 2009
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    Nothing is safer than the way I did it. :D

    I let UL and CSA be the determinant of what is safe...
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    A DIY circuit board, your assembly skills, DIY project box, DIY fuse, DIY surge protection and DIY power cord restraint?

    PLEASE buy a little LED nightlight and plug it in to see if you have power or use a cell phone charger (look for UL or CSA ratings on anything). I am not a fan of new DIYers making mains powered devices that could eventually electrocute or cause a fire in a house.
     
  13. technokid

    Thread Starter Member

    Nov 29, 2014
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    .....again, this method requires connection to the mains, even though, the transformer may provide isolation and secondly, it requires plugs, sockets, etc. extensive modification around the mains conductor, where space sometimes does not permit.
     
  14. technokid

    Thread Starter Member

    Nov 29, 2014
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    The circuit is to be placed in an enclosure, where anyone, can gauge if mains voltage is applied to the load from outside the box. The second point, if the box is opened up, by an experienced person or not, would not by accident get electrocuted, thinking because it is powering an led, the voltage would not be dangerous. So safety is behind the whole concept. If a I wanted to use a direct connection to the mains, isolated or not, there are plenty of examples on the net. Hence, this special request.
     
  15. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    You may just have to experiment. e.g. wrap a few turns of the mains conductor around a toroid and add a few turns connected to a low current LED and see whether there is enough current to light it up; add more turns if necessary. As mentioned previously the load must also be connected for the LED to light.
     
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    If you are mounting this inside a metallic enclosure, then here is how I do it. When used in a USA 240V system, the LED and diode end up being only a couple of V from ground.
     
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  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    How will you get a secondary voltage when there is no voltage across, or current through the primary on a current transformer with no load (current) on the conductor?
    http://www.electronics-tutorials.ws/transformer/current-transformer.html

    Max.
     
    Last edited: Nov 29, 2014
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  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you are relying on load current through the mains lead to induce current in a coil to power the LED then you could well have a circuit with mains voltage on it but no warning light. That is potentially (no pun intended) dangerous. It would be safer to have the LED powered when mains voltage is present.
     
  19. #12

    Expert

    Nov 30, 2010
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    Has anyone mentioned that you can buy a hot wire indicator with an LED at Home Depot for about $11? It's as much a part of my tool box as an amp-clamp.
     
  20. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    For some reason he doesn't want a bare wire connection to mains. I don't know how he plans to wrap one leg of a wire (hot) in a Romex sheath around a toroid without making a disconnect. Still waiting for this aha moment to unfold (or to be told I misunderstood his requirements).
     
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