Cold you clarify a few topics on the restricted themes?

Discussion in 'Off-Topic' started by The Kadet, Apr 28, 2016.

  1. The Kadet

    Thread Starter New Member

    Apr 27, 2016
    7
    0
    Hello

    Cold you clarify a few topics on the restricted themes?

    "
    1. Restricted topics. The following topics are regularly raised however are considered "off-topic" at all times and will result in Your thread being closed without question:
      • LEDs to mains
      • Transformer-less power supplies
      If You come across a thread or post discussing any of the above topics please report the thread so We can close, and if necessary remove, the offending thread/posts.
    "from: http://www.allaboutcircuits.com/user-agreement/

    what do you mean a as led to mains? is it some sort of fuse?

    and second what are "Transformer-less power supplies"? topics:

    Some motion detectors and other sensors use a kind of Transformer-less to step down voltage current.

    Older TV vacum tube ones used a kind of Transformer-less power amplifier to produce the high voltage neded to cause florescense.

    some info ive got on you tube:

     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    No, they can't. :rolleyes:

    (I be sharpinin' my poking stick for this thread though!) :D
     
  3. The Kadet

    Thread Starter New Member

    Apr 27, 2016
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    0
    if they cant just delete it
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    The basic issue is that the owners of the site feel that the combination of the skill level of many of the members of this site and the inherent and easily overlooked risks of these types of circuits presents a safety hazard that they don't want to foster.

    As I see it, the issue comes down to the fact that the circuits present too high a likelihood that high (and potentially fatal) voltages and currents can become present in circuits that are seen as being low voltage and "safe" to tinker with while energized. People, particularly newbies, poke around in low voltage circuits (such as the type of which LEDs are often a part) with their fingers without any regard to touching energized portions since it is viewed as safe to do so. That habit tends to carry forward to circuits in which LEDs are connected directly to the mains or in transformerless power supply designs. When a circuit uses a stepdown transformer to go from the mains to the low voltage circuit, there is a very clear and easily seen and understood demarcation between the high voltage and the low voltage portions of the circuit and even most newbies respect the dangers that the high voltage section presents.

    Note that the owners have never said that LED-to-mains or transformerless power supplies are "bad" or that they have no place in products. It is merely their view that, in a forum such as this, that they present too high a risk to too large a fraction of the people that might come across them here and only learn enough with which to kill themselves. You may or may not agree with their view. I may or may not agree with their view. Neither of those is relevant since neither you nor I own this site. Given the broad latitude of topics that can be discussed, observing the owners' dictates in this regard is not a very onerous burden.
     
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    Can you cite a model number of the motion detector system?

    Got a schematic illustrating that?
     
  6. BR-549

    Well-Known Member

    Sep 22, 2013
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    I can remember old tv chassis that had transformerless supplies. A polarized plug.

    And you can find hundreds of circuit schematics and manufacture app notes on powering all kinds of sensors and InternetOfThings circuits, that tie directly to 120 or 220 VAC.

    These are interesting and valid circuits. But they are not for newbies or hobbyist.

    One should gain a lot of experience with manufacturers application notes before attempting any design.

    It is a new circuit art, but very UN-forgiving.
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
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    There were many tube tvs, radios and audio amps that had transformerless power.

    And the same thing was done when transistors came along too.



    aa5diaa.jpg aa5oct.jpg



    These were called the American 5. I still have a few of these.
     
  8. BR-549

    Well-Known Member

    Sep 22, 2013
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    I was taught electronics in the 60s and 70s. At that time, 300 V secondaries and 300 V screen and plate voltages were common.

    Technicians were taught high voltage safety at the git go. One handed work.

    This is probably why I thought the transformerless power supply band was silly.

    But today's techs are trained on very low voltage. If a tech today, suspects a faulty transistor or resistor, He can pinch the device under power and feel for heat.

    You try that with a tube circuit and you'll end up on your ass.

    Plus the fact that I don't think they teach the fundamentals like they used to.

    A lot of people who claim to have degrees, ask a lot of fundamental questions.

    If I owned this site, I would continue the band.

    One would probably have to take some electrician courses to learn high voltage safety.
     
  9. dannyf

    Well-Known Member

    Sep 13, 2015
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    Tons of them.

    Some tube radios are that as well. Well known to many repairmen, :)
     
  10. JohnInTX

    Moderator

    Jun 26, 2012
    2,347
    1,029
    Indeed. The standard 5 tube superhet sets frequently had no isolation nor polarized plugs. 'Safety' was ensured by a plastic (bakelite) case and knobs. One of my early introductions to electricity was touching the bare knob shaft of one of these plugged in the wrong way around - shocked me pretty good.

    I didn't expect that sort of thing and that's why the restriction here. While it's obvious that when you are intentionally working with some line-powered load, you expect and respect the associated hazards. Its unreasonable to expect that touching a flashing LED blinkie or plugging in a comms cable to your PC should knock you or some innocent passerby across the room. That's the difference.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
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    There is nothing wrong with transformerless power supplies (when done properly by those who are well aware of the dangers and how to mitigate them)..
    But this is an internet forum where anything from an 8 year old child to an 80 year old professional Engineer are free to post so one must use caution and prohibit certain discussion topics that could get someone that isn't aware of the dangers hurt or killed.

    Its no different than a gun.. Guns are totally fine when in the hands of someone who is well aware of the dangers.. But put a gun in an untrained childs hands and well you know the rest.. population control
     
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Here's what I get out of this.

    Line voltage + resistor/capacitor + LED = not okay. (It will kill you)

    Line voltage + resistor/capacitor + zener diode/voltage regulation circuitry = not okay. (It will kill you)

    Line voltage + resistor/capacitor + mini neon bulb = Okay. (You'll be fine. Everyone's got to learn sometime.)

    line voltage + rectifier into capacitor to feed a SMPS = Okay. (You'll be fine. Everyone's got to learn sometime.)

    line voltage + rectifier into capacitor to feed a DC motor = Okay. (You'll be fine. Everyone's got to learn sometime.)

    Line voltage + transformer to any ungodly voltage and current you wish = Okay. (You'll be fine. Everyone's got to learn sometime.)

    Low voltage AC + transformer to any ungodly voltage and current you wish = Okay. (You'll be fine. Everyone's got to learn sometime.)

    Low voltage DC + inverter circuit + transformer to any ungodly voltage and current you wish = Okay. (You'll be fine. Everyone's got to learn sometime.)

    Any home residential or light commercial wiring with no clue which end of a battery goes up = Okay. (You'll be fine. Everyone's got to learn sometime.)

    Simply put line voltage plus any type of solid state diode based device that either emits light or limits voltage will kill you. Everything else, Heck, it's a great way to learn the fundamentals of electricity with! :D


    So go ahead, rectify that 120/208/240/277/480/600+VAC home or commercial line feeder and dump it into a capacitor bank the size of a refrigerator then run an electric motor the size of a bus or megawatt class SMPS or inverter circuit to drive your home built DIY particle accelerator or gigavolt Tesla coil! :cool:

    You be just fine as long as you don't use a LED or zener diode in series with a resistor or capacitor that is hooked up to the live side of your power feed anywhere on the system. :rolleyes:

    (Poke Poke Poke.) :p
     
  13. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I remember the older radios, but not the older televisions the TS mentioned.

    Now, I would still like the model number of the motion detector ...... The TS alluded to.
     
  14. BR-549

    Well-Known Member

    Sep 22, 2013
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  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I don't find anything wrong with transformerless devices.

    However, litigation gets out of hand at times, for instance:

    http://money.cnn.com/2016/04/26/technology/snapchat-speed-filter/

    https://www.washingtonpost.com/news...cedes-caused-by-teen-girl-using-speed-filter/

    But wait, there's more laws to be passed. One will require your cellphone to warn you about using the phone while driving where you have to "electronically" agree that you are not driving to use it. Since there are multiple instances of people texting while walking, the speed filter could be used there too. After all, we require the government to protect us from our own stupidity. [/sarcasm]
     
  16. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Every motion detector I have ever taken apart has used a transformerless power supply.

    Same with most any programmable digital outlet timer.

    And wireless remote outlets as well.

    Got a set of flashing Christmas lights that can change pattern, incandescent or LED? Transformerless power supply in those too.
     
  17. wayneh

    Expert

    Sep 9, 2010
    12,126
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    There ubiquity explains the reason for the ban. You don't need a blanket ban on something that happens rarely - you can deal with it on a case-by-case basis. A blanket ban on noobs doing LEDs to mains saves a lot of time otherwise wasted thinking about it. Ban it. Done, move on.

    The downside is a very imperfect and "unfair" discrimination that allows dangerous projects to go forward while some that might be fine get bounced. Boo hoo.
     
  18. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,290
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    When I was going to school I fixed TVs. I hated those hot chassis radios and televisions.
    [​IMG]
     
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