Forum legality of AC mains circuits?

Discussion in 'Off-Topic' started by THE_RB, Mar 12, 2014.

  1. THE_RB

    Thread Starter AAC Fanatic!

    Feb 11, 2008
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    Hi, I am working on a fan speed controller for a workshop AC mains (shaded pole) fan.

    The idea is to use a standard TRIAC style AC controller system (which are ok to discuss as far as I know?) but the circuit will use a closed-loop sensor to sense the fan speed and keep it exact. Fans tend to run faster/slower due to bearing friction changes etc, and closed loop control will also allow me to run it very slow for gently blowing away solder fumes etc.

    My question is related to whether it is ok to show and discuss the circuit as all parts of it operate at AC mains potential, similar to a TRIAC speed controller like this;

    [​IMG]

    However there will be extra components added for the closed loop sensor control.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Funny I raised a very similar questions here. http://forum.allaboutcircuits.com/showthread.php?t=80693 And I was kind of disappointed that none those supervising the site was able to give an answer. But I much later had a PM with MrChips regarding primary switched switchmode powers after such a thread got closed by him
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    Because such a device is closed box (not a power supply or LEDs) we allow it. It is standard off the shelf technology, basically what you buy if you go to a hardware store.

    We do not always get it right. We are human, if we make a mistake we move on and learn from it.
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    I do not think that argument holds water Bill. As long as Roman Black want to build his TRIAC AC controller from start with discrete components. And strictly speaking such a device will not legal to connect to mains by international laws. As it will lack proper approval. Then it comes to safety very little differ the typical light dimmer from a transformerless power supply. I have none what so ever doubt that Roman Black will be able to make good working triac controller. My concern is with not so skilled members. As not built properly such a device is as potential dangerous as a transformerless power supply then built as a homebrew. I know we have had request from a beginner in electronics. That wanted to build a light dimmer controller regulate a 2 KWatt heating oven at night or then he was out of the room.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a triac dimmer circuit will not control the speed very well on a shaded pole motor. a brush type motor works with this type of control, but a shaded pole will have a small range of change, just like if the voltage goes down. it needs a variable frequency drive to regulate the speed.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I'd say carry on and see where it goes.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I agree with the DC motor for that purpose, especially in place of a triac 50Hz controller, the shaded pole motors do not control well down to a few rpm.
    If this is a one-off for the shop, I would have looked at a automotive fan from a wrecker, the modern auto fans now use PWM for fan control and can control nicely down to low rpm, without the possible need for feedback.
    Max.
     
  8. Sparky49

    Active Member

    Jul 16, 2011
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    Best thing to do would be to PM a copy to a mod and ask their opinion.

    Worst case scenario you get to post it, but it is later decided that it goes against the rules and is taken down.

    Problem over.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    You have one mods take on it, 3 to go.
     
  10. #12

    Expert

    Nov 30, 2010
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    I can do a serious rant about the codes, laws, and regulations declaring that nothing is allowed unless they inspect and approve it. Strantor and I make a living designing and building control circuits that are, "not approved" by anybody except us.

    This requirement is as bad as the Sziklai pair which I have been using in my designs for 40 years. Why is the "double invert" circuit suddenly named after a person? He has a college degree and I don't?

    On the same line of thought, somebody, "discovered" Australia and the Pitcairn Islands? I don't think so. The inhabitants knew they were there all the time.
     
    strantor likes this.
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Same reason whoever wins the war is right and gets to write the history book on it.

    P.S. I don't believe anyone was on Pitcairn until the Mutiny? :)
    Max.
     
  12. #12

    Expert

    Nov 30, 2010
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    I think you're right. I was thinking of the island where the Bounty was collecting breadfruit seedlings.

    Oops. My bad.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    I have seen newbies stab their fingers with DIP ICs, blow up resistors, capacitors and diodes, stick a pair of needle nose pliers into AC outlets and burn themselves on soldering irons.

    We can't protect every soul from every possible hazard.

    To be honest, I too am confused as to what is allowed and what is not allowed on AAC.
    I have my personal opinion but would have to go with the consensus of moderators who were here before me.
     
    Last edited: Mar 12, 2014
  14. t06afre

    AAC Fanatic!

    May 11, 2009
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    Do not tell me. I almost lost my eye to LM723 dip that exploded on a vero board during close inspection. The plastic covering the silicon chip shot out as rocket. And made a bleeding cut just above my eyebrow
     
  15. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I just post whatever I feel like and let someone else decide whether it can stay or not then again I feel that everyone is their own safety officer and no one is more responsible for their safety than themselves.

    If they do something stupid and hurt himself by taking advice that was way over their heads then thats their fault and hopefully they learn from it.
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    And since you injured momma's precious child, she hired a lawyer to hunt you down to sue you. Then the lawyer looks at the worth of the website and decides the website owner could sell the site to pay the fine.

    If there should be a discussion on where safety applies, we can have one. A lot of "mains" type projects could be accomplished using a 1:1 transformer.

    If we were going to go by electrical shock safety, we wouldn't discuss anything with a voltage above 30V as the body resistance can be as low as 300 ohms ... under certain environmental conditions, giving way to the potential shock current of 100 mA.

    The other option is to have a user agreement, digitally signed, that the user does not hold the website liable for the advice given or the advice taken. This is a use at your own risk website.

    Once again I'll state that anyone can give whatever advice they want off site, via email or private message, that runs contrary to whatever rules are enforced by any website forum.
     
    Metalmann likes this.
  17. THE_RB

    Thread Starter AAC Fanatic!

    Feb 11, 2008
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    Thanks for the feedback Bill. I planned to use standard modern technology practices like a PIC micro in the control circuit, supplied through a mains rated X2 capacitor (like pretty much every light dimmer and electronic light switch you can buy these days).


    I understand that. This is not a commercial venture, it's a fun hobby project for my workshop fan. The legality would be no different than any other mains powered hobby project, of which the forum has thousands.

    You made a good point though about beginners; that they may try to build one but have poor skills and poor safety practices. But doesn't that also apply to the majority of mains powered projects?


    I used to think that too, but all these small desktop and pedestal fans with shaded pole motors just run in "slip" for the lower speeds. Often they just use a capacitor to reduce motor voltage and current to get a lower speed.

    The trouble is that the low speeds have very low motor torque, which is close to the friction loss of the bearings. The the low speeds can be unreliable depending on bearing lube and heat expansion etc.

    I have never done it but I think with a speed sensor and PIC micro in a closed loop system the fan could be run really slow at a steady speed. The micro will provide as much power to the motor as is needed to maintain that exact slow speed.

    Regarding the circuit my goal was to make it simple to build. If I was to add a small mains transformer and bridge to power the PIC that is more work and space required, and would also then require an optocoupler to the TRIAC and on my 240v mains that requires extra high voltage resistors/caps etc. And maybe need a second opto too for zero-cross detection.

    So my plan was to use a half wave capacitive reactance supply consisting of 2 diodes, an X2 mains cap and a zener. The PIC should only need 3mA or so average. Then the PIC output pin could connect direct to the TRIAC gate. The same simple system is used in many small modern mains devices that I have seen/repaired and is a modern standard.

    I'm still concerned about beginner safety issues, but the issues that I forsee also apply to many other mains speed controllers which are posted here; that the entire circuit and all parts run at "lethal" mains potential.
     
    Last edited: Mar 13, 2014
  18. Georacer

    Moderator

    Nov 25, 2009
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    Sometimes enforcing the AAC ToS can be very problematic and absurd. I would know that. And rest assured that I don't always agree with them.

    In general, we examine each post and report and decide separately. No two posts are the same (except for spam, maybe).

    In the transformerless power supplies case, we have a thread on the Mods' section where we try to write a little clarifciation.

    In this case, I'd say that it's not a power supply, it's a control circuit and I'd go forth. Nothing is said in the ToS on control circuits.

    This thread has my approval, so far.
     
  19. Metalmann

    Active Member

    Dec 8, 2012
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    Here's another good explanation of the hazards of milliamperes:

    http://www.elec-toolbox.com/Safety/safety.htm

    "It's not the voltage but the current that kills.
    People have been killed by 100 volts AC in the home and with as little as 42 volts DC. The real measure of a shock's intensity lies in the amount of current (in milliamperes) forced through the body.
    Any electrical device used on a house wiring circuit can, under certain conditions, transmit a fatal amount of current.
    Currents between 100 and 200 milliamperes (0.1 ampere and 0.2 ampere) are fatal.

    Anything in the neighborhood of 10 milliamperes (0.01) is capable of producing painful to severe shock".:eek:;)
     
  20. Metalmann

    Active Member

    Dec 8, 2012
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    And, another one:


    "A common misconception is that larger voltages are more dangerous than smaller ones. However, this is not quite true. The danger to living things comes not from the potential difference, but rather the current flowing between two points.

    The reason that people may believe this, can be explained by the equation V = IR.

    Since V is directly proportional to I, an increase in voltage can mean an increase in current, if resistance (R) is kept constant.


    The amount of damage done by the electric shock depends not only on the magnitude of the current, but it also on which portions of the body that the electric current is flowing through. The reason for this is that different parts of the body have difference resistances, which can lead to an increase in current, evidenced by the formula V = IR.


    An interesting fact to note is that it takes less alternating current (AC) to do the same damage as direct current (DC). AC will cause muscles to contract, and if the current were high enough, one would not be able to let go of whatever is causing the current coursing through the body.

    The cut-off value for this is known as the "let-go current".

    For women, it is typically 5 to 7 milliamperes, and for men, typically 7 to 9 milliamperes. This is dependent on the muscle mass of the individual.


    In general, current that is fatal to humans ranges from 0.06 A to 0.07 A, depending on the person and the type of current."


    http://hypertextbook.com/facts/2000/JackHsu.shtml
     
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