Discussion: Helping novices work with transformerless AC circuits -improving safety or tempting fate

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
20,911
(Moderator's note: This safety discussion was broken off from this thread:
https://forum.allaboutcircuits.com/threads/optimize-this-circuit-power-supply-help-needed.142469/#post-1203594)

The user agreement specifically mentions transformerless power supplies, but I believe the intent is to protect people from being exposed to high voltages. So, even if you added an isolation transformer, there would still be high voltages present.
The only answer would be to restrict ALL posts to the considered extra safe level, no higher than 50vac.!:rolleyes:
All of the queries frequently presented on the subject of SCR/TRAC dimmers etc would be deleted.
Plus all the 240v appliance problems and 3ph & 1ph phase motors questions, just to name a few.
The end result would be a drastic reduction in forum traffic.
Max.
 
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dl324

Joined Mar 30, 2015
10,984
Most said newbies seem intent on that to start with - shutting the door in their faces isn't going to save any lives.
I just didn't want to help someone win a Darwin Award. Rectified 230VAC is going to give a potentially lethal DC voltage (over 300V). The instructable creator knew that and used multiple resistors in series to overcome the maximum working voltage.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
20,911
My philosophy is that I would rather assist and advise someone who is learning than shut the door on advice and pretty much knowing he is going to seek the knowledge anyway, but alone and unadvised.
It is rather naive to think that someone is going to throw up their hands and give up when the door is closed.
Max.
 

ian field

Joined Oct 27, 2012
6,539
My philosophy is that I would rather assist and advise someone who is learning than shut the door on advice and pretty much knowing he is going to seek the knowledge anyway, but alone and unadvised.
It is rather naive to think that someone is going to throw up their hands and give up when the door is closed.
Max.
That's been my line all along.
 

Alec_t

Joined Sep 17, 2013
11,406
I usually throw in a warning in my posts when high voltage is involved. As said above, newbies are going to go ahead with or without our help anyway.
 

tindel

Joined Sep 16, 2012
716
We can all agree that working directly off-line is a stupid and dangerous proposition. To that end, I have always thought that the intent is to encourage development using a transformer for safety purposes. If you're working on a off-line supply (isolated or not) a transformer should be put on the input to isolate the circuit from earth for safety purposes. I keep an isolation transformer on my bench for this very purpose. You probably do to. I don't think a off-line LED strand would be discouraged if the user was going to develop the product using an isolation transformer - even if the intent was to later remove the transformer, but I'm not a moderator - so perhaps I'm wrong about this - I'm not sure it's been discussed either.

Even if you are helping, the problem with the internet based help is that you are not physically there to ensure their work is safe by verifying proper isolation transformer connections, proper technique (one-hand rule), proper tools and CAT ratings, connecting scope probes while the power is off and taking measurements after the power has been turned on, how the oscilloscope probe ground defeats the isolation transformer and potentially makes the circuit more dangerous, etc. These things are common sense for people like us, but they have the potential to be deadly for the uninitiated.

I have shied away from discussing high voltage circuits entirely with people that I do not know have the skills to work with such devices. I would teach a small child if I knew they were level headed and careful and I could be present so that I could correct subtleties in how they worked with HV. On the other hand, I would not teach some full grown adults that I know are not stable. When considering teaching HV techniques to someone their character comes into play IMHO. This is something that is hard to judge over the internet.

Finally, if someone comes with 1 post to their name asking for circuits for a transformerless supply they probably don't know much about HV and they should be steered to LV experimentation first. By the time you're ready for the jump to HV, you know many of the techniques already.
 

MrChips

Joined Oct 2, 2009
21,336
While there are obvious safety concerns when working with high voltages, I was under the impression that the requirement for using AC mains transformer was to provide galvanic isolation from AC mains supply, not for HV reduction.
 

nsaspook

Joined Aug 27, 2009
7,356
While there are obvious safety concerns when working with high voltages, I was under the impression that the requirement for using AC mains transformer was to provide galvanic isolation from AC mains supply, not for HV reduction.
That's my impression too. The vital safety aspect is not the HV as the experimenter builds something, it's the increase in possible pathways for lethal or dangerous current levels above normal leakage while touching things or shorting wires to things we normally would consider 'safe' with transformer coupled AC circuits.

 
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Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
20,911
I have an old original copy of the SCR/Triac experimenters manual, I referenced here https://forum.allaboutcircuits.com/threads/which-thyristor-to-use-for-power-electronics.142489/
It has a Foreword:

NOTICE TO EXPERIMENTERS.
G.E. has used reasonable care in selecting circuits and suitable components for the average hobby'ist or experimenter.
However, no responsibility is assumed by GE for any consequences in their use.
Some of the more complex circuits in this manual should only be attempted by those having experience with wiring techniques and mechanical construction.
YOU are a best judge of your own capabilities!
Max.
 

Tomy983

Joined Nov 22, 2017
9
I have an old original copy of the SCR/Triac experimenters manual, I referenced here https://forum.allaboutcircuits.com/threads/which-thyristor-to-use-for-power-electronics.142489/
It has a Foreword:

NOTICE TO EXPERIMENTERS.
G.E. has used reasonable care in selecting circuits and suitable components for the average hobby'ist or experimenter.
However, no responsibility is assumed by GE for any consequences in their use.
Some of the more complex circuits in this manual should only be attempted by those having experience with wiring techniques and mechanical construction.
YOU are a best judge of your own capabilities!
Max.
I like this lines.
Probably doesn't matter much, but since this discussion started from the thread I opened, I just wanted to give you a little background..

I am an electrician, I work on what we consider by standards low voltage single phase 230V and three phase 400V system every day. Sometimes even on energized circuits.
And no, I do not know how to design a transformerless supply. Trying to learn though..
Finally, if someone comes with 1 post to their name asking for circuits for a transformerless supply they probably don't know much about HV and they should be steered to LV experimentation first. By the time you're ready for the jump to HV, you know many of the techniques already.
I understand what you are saying, but assuming that a person who doesn't know what might look to you basic AC mains electronics circuits can't appreciate the risks involved isn't fair either. I remember, for instance a guy who works on medium voltage substations (9kV) asking me how to connect an LED to 24V..
I did understand though the concerns and I will not argue whether it is or it isn't possible to talk about over 50V in this forum. This will not stop me though, like it does not stop any guy at home to connect line and neutral to a switch and then call us because he can't power the house anymore. If I asked for help, you then have the chance to educate and teach. If I can't get help I will try anyway. But I think the risk might be higher.
 

Reloadron

Joined Jan 15, 2015
5,508
My thinking on much of this is relatively simple, nobody can save people from themselves. Reading threads of years ago I noticed a difference in which threads were closed by moderators. Moderators being people seemed to view material differently. What Moderator A found acceptable Moderator B found in violation of forum rules. While I can appreciate the thinking of forum owners as to any remotely possible liabilities I have yet to see a published case file where an online Internet forum was held liable for someone getting electrocuted as a result of reading advice in an online Internet forum. While we joke about Darwin Awards one fact remains true in that nobody can save people from themselves.

Every electrical or electronic enthusiast starts somewhere. We have all seen threads asking something and we have all seen responses to the effect of "if you need to ask that question, you shouldn't be working with that circuit". Enter the safety police force and things generally go downhill from there. Maybe a better answer would be "you do understand the possible consequences of working with mains voltage and ..." Then answer the question. Simply put, rather than come across as an almighty use a nicer gentle approach.

People ask questions and new members answer to the best of their ability. If a forum chooses to limit working voltages or start getting into a need for defining isolated voltage sources the forum is going to loose traffic. As a forum member my visits here are governed by the rules. My job is not to critique post or "memberate".

Purely my opinion....
Ron
 

ian field

Joined Oct 27, 2012
6,539
I just didn't want to help someone win a Darwin Award. Rectified 230VAC is going to give a potentially lethal DC voltage (over 300V). The instructable creator knew that and used multiple resistors in series to overcome the maximum working voltage.
Its a common occurrence that newbies have turned up here with dangerous ideas - no one here set them off in that direction.

Obviously the forum must guard against anyone here sending the unsuspecting off in the general direction of a Darwin award - but if you see someone stumbling toward the precipice, there is a responsibility to guide them to safety rather than look the other way while they go over.
 

philba

Joined Aug 17, 2017
960
This is kind of a slippery slope. I'm not sure where the line should be drawn, though. Clearly, people doing things on a par with that electrocution guitar should be highly discouraged but there are legitimate transformerless circuits and it's possible to make them safe. Because it's impossible to truly judge someone's competence, I think ruling them out is a reasonable restriction. However, to take it to the next step per Max's first post in this thread is too restrictive.

Personally, I avoid helping someone do projects that have a life/safety component. The fellow with the Arduino controlled syringe springs to mind. A circuit or programming error could be fatal and I want no part of that. But that's an easy call. Helping someone do a phase controlled dimmer is probably ok since reasonable precautions are all over the internet. In between? It's not always obvious.
 

crutschow

Joined Mar 14, 2008
25,122
Certainly the first rule is that anyone working on a line powered device (even if it has a transformer) is to only plug it into a GFCI socket.
That way, even if the hot line is accidentally touched (or someone puts his oscilloscope ground clip on the hot line) the results should't be lethal or catastrophic (although he likely will learn not to do that again :eek:).
 

tindel

Joined Sep 16, 2012
716
I understand what you are saying, but assuming that a person who doesn't know what might look to you basic AC mains electronics circuits can't appreciate the risks involved isn't fair either. I remember, for instance a guy who works on medium voltage substations (9kV) asking me how to connect an LED to 24V.
To be fair - I didn't even look at your original post. I knew where it originated without looking. It happens several times a year that someone comes here and their first post is about some non-isolated something or other. With one post I know nothing about your background. Nothing. I'd rather assume that the poster doesn't have the required experience and not give them any information than give them the information they seek and potentially leave myself open for litigation.

Most people know that voltages over about 50V can be dangerous. I've literally been shocked by 50V thinking it wasn't high enough, but I was wrong, wrong, wrong. I knew of an electrician that was working in a electrical box, doing things that he shouldn't have been doing, made one too many wrong moves, and he didn't live to kiss his kids good night again. Very sad. Even "low voltage" mains are lethal. I don't get this bravado thing that electricians have bragging about working on energized stuff. It's just stupid and not required to do the job. Sure measure the voltage and current, but before you touch a wire, turn off the switch. At the end of the day it's your life, and most have been shocked by 120V or 240V (myself included), but I'd rather avoid it if I can.

I once got my hand over rectified 277V (400Vdc). I am very thankful it just got my hand. I felt it for about 3 days after the event. Painful.

@crutschow thanks for the tip of using a GFCI - that's not something I had not considered doing, but would be very simple to implement in my lab. It's also not something we did at a LED lighting company I used to work for - I wonder why we didn't consider it.
 

Reloadron

Joined Jan 15, 2015
5,508
Looking back, before Al Gore invented the Internet, and when the Transistor was in its infancy, how would today's Internet Electronic Enthusiast Forums have handled voltage and the transformers that deliver higher voltages? Basic power supply designs consisted of B+ voltages of 250 to 1.0 KV for tube plate voltages. How many electronics enthusiast were electrocuted building a power supply to power a pair of 1625 tubes (or valves) used as a final in a home brew ham band transmitter? Before the Internet could tell me shoving a butter knife in a toaster was a bad idea I shoved a butter knife in a toaster and quickly figured out it was a bad idea. Nobody could have saved me from myself. How many warnings does it take to convey to people that peeing on B+ is not a good idea? None of my early electronics books even mention any warnings, maybe the authors wrongfully assumed people would not pee on B+?

During my career I was blessed to have a great department head. I remember many discussions on new designs which went:
Mike: Ron, we need the design to be fool proof.
Ron: Mike, I can't make it fool proof.
Mike: Why not?
Ron: Because fools are very ingenious people.

That was where it ended.

Ron
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
20,911
I recall when I was in basic training in the Royal Signals, one instructor was showing us how to change the frequency taps on a transmitter, he warned anyone that got injuries while doing it without first ensuring the power was off would be charged.
The next day when we went in he had sticking plaster over all his finger tips!
Guess Why?:p
Max..
 
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nsaspook

Joined Aug 27, 2009
7,356
How many warnings does it take to convey to people that peeing on B+ is not a good idea? None of my early electronics books even mention any warnings, maybe the authors wrongfully assumed people would not pee on B+?
When people see a Tiger (B+) we naturally think it's dangerous (Yes, I've seen the effects of a person touching a PA tube at full power because fools are very ingenious people). Hidden counter-examples are also dangerous. Our electrical intuition leads us to think a 5vdc LED supply + and - wires are not dangerous because of isolation. When transformer isolation is missing we can be fooled on what's dangerous easily by measuring voltages from a reference point other than our bodies ground reference to the AC line potential possibly on those + and - wires..
 
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