The transformerless supply question

[tvtech]

Hi Guys

There are forums out there that do not allow any discussion or whatever on this subject. So they (the forums) don't like anything even marginally related to working on Mains without isolation.... Something to do with the owners of the site worrying about Liability and all...

Here is the problem as I see it.....how can people learn and respect things like transformerless Power Supplies if they are not even allowed to mention them???. A case of "just don't do it. It is dangerous". End of story. And I call BS.

Non isolated power supplies have been around a long time. They are used everywhere. From simple Mains indicators to many more complicated things..

Understanding and respect will educate and help people to come to terms with this most efficient and reliable kind of cheap supply. Not just saying it is crap. Because it is not. Maybe I am having a rant here. Maybe I want to educate. Maybe I just love ETO because I can talk about it here..

Now you see Guys why at ETO we have warnings with HV stuff. We caution people rather than say "don't do it".

How can you possibly learn about something if you are not even allowed to discuss it??

You see. It just makes people more curious

Regards,
tvtech

 

[ronsimpson]

How can you possibly learn about something if you are not even allowed to discuss it??
You see. It just makes people more curious

My mother gave me a list of things not to do at the university.
In the first semester I made it through the list. (not including the parts about girls) That took longer.

 

[tvtech]

LOL ron

I am passionate about this whole non- isolated thing though . Obviously the girls were non - isolated.....

Please, please keep this thread on track. I would like to hear what members here think about this whole thing about isolated Mains and all and when it it is necessary and when not. Could be a really good thread.

Regards,
tvtech

 

[canadaelk]

tvtech: You are not passionate about this subject, you are obsessed with it!

A trained and qualyfied electrician or electronics tech was taught how to protect her(him)self and others from harm and knows how to build a safe product. A hobbiyist mostlikely does not have that knowledge!
A tech also knows haw to retro-engineer or design his own product and calculate the values for parts for the application and should not need help or a discussion group!

If you are so passionate about this, start your own forum. Call it the "Electrocution Hobbyist" and see how many sponsors you get. Make sure you have good liability insurance.

In the meanwhile (to prevent electrical shock): Don't touch this, don't touch that and dont touch that either. And stop touching yourself! E

 

[JimB]

TVtech

In the recently revised rules for the forum, we have the following statement on safety:

***************************************************************************************************************************************
Safety
Safety is important to everyone.
Ultimately you and you alone are responsible for your own safety regarding any circuit, device, or system you are working on.
Keep in mind that some members here may be as highly skilled and experienced as others are incompetent and careless.
That means that no one but you, the end user, can see and accordingly judge the potential dangers that others' advice or suggestions may hold for you, based on your present skill sets and knowledge of what you are attempting to do.
If you are not sure if something someone says is safe or legal, ask follow-up questions and do more research before attempting it. It is ultimately your responsibility to determine whether or not a solution is safe and legal. Use the information you get here at your own risk and to the best of your own judgment.
***************************************************************************************************************************************

In my opinion that covers the "liability issues".
As you comment, there is at least one popular electronics forum which forbids discussion of automotive topics and transformerless power supplies, that is their perogative to do so.
Is it helpfull? Probably not.

As far as transformerless power supplies go, it is my opinion that they have no place in amateur electronics, UNLESS they are incorporated into a fully engineered enclosure which prevents unwanted contact with a potentially live circuits, in accordance with modern safety requirements.
How often is that going to happen? Not very often!
Of course in the process of developing a transformerless power supply, it is necessary to have it exposed on the workbench.
Appropriate precautions should be taken, such as beware where you put your fingers and use an isolating transformer during develeopment. I have such a device but I doubt that the average 3rd world tyro out to save on the cost of a simple 10VA mains transformer has the luxury of a 1 kVA isolation transformer. (Mine cost me nothing, but that is the upside of being around electronics for 50+ years).

If you will allow me to drift the thread a bit, but to topics which in my opinion come into the same category...

Radio transmitters.
Someone will come on the forum and ask about building a transmitter which will do XYZ.
When it is pointed out to them that this is a bad idea both technically and legally, they retort that "in my country" it is not illegal, there is no one to cause interference problems to, etc...
All based on there total lack of knowledge of RF matters.
Attempts at enlightening them usually falls on deaf ears, and they wander off in a huff.

Back to the main programme...
And so it is with transformerless power supplies, trying to enlighten those who do not want to be enlightened is a futile activity.

JimB

 

[killivolt]

I've seen Tech's do things that make me shutter; all survived. It isn't just the untrained that do things without thinking it through. However, these people will do it anyway just as "JimB" said *they wander off in a huff*
so when they go; they go to some Youtube video or some blog or somewhere to find the information they are seeking to complete their deathly device.

All you have done is motivate the Person to seek out things on their own to less respective area's of the net where in information is found and utilized by ignorant people. Although rather; I think it's better to instruct best practices on devices that are currently on the Market; instead of shunning. How many of you have taken something apart like that just to see what's inside? Long before you became an EE. If you say no; I would be surprised.

That type of person will do it, and possibly be more incline to do harm to themselves or others in the process.

 

[Miles Prower]

Here is the problem as I see it.....how can people learn and respect things like transformerless Power Supplies if they are not even allowed to mention them???. A case of "just don't do it. It is dangerous". End of story. And I call BS.

Non isolated power supplies have been around a long time. They are used everywhere. From simple Mains indicators to many more complicated things..

They didn't call that topology the "suicide box" for nuttin'.

Take a look at This Schemo. If you plugged that in so's the hot side went to the plate of the 35W4, no problem. However, if you connected it the other way, nothing would change as it would work just the same, so you never know when you guess right. But, in that case, the chassis would be hot to any ground. Come between the chassis and that ground, and ZZZZAP! Also, notice the use of a SPST power switch. If the hot side is connected to the chassis, the chassis is still hot to ground even if the set is switched off.

Here's another one: take a look at This Vid. Pay close attention when he shows you the bottom of that radio. See those two screws on the bottom? These are in direct contact with the chassis, and will go hot to ground. Picking it up, even if turned off, could be a shocking experience if you're also grounded.

For a radio or TV set, it doesn't make any difference since the internals can be isolated. However, that wasn't the only devices operated straight off the mains. The Lafayette KT-92 amp kit (circa 1959, schemo @ 1:25) also used a straight from the mains PS. That's especially bad since you have no idea what the end user is going to plug into it. How many CD players, computer sound cards, tuners, and so forth can stand up to 120Vrms? Low power guitar practice amps likewise were made like this, and there were electrocutions and near-electrocutions from hot guitars. For amps, a PTX-less power supply is a REALLY bad idea. It was a bad idea then, and it hasn't improved with age.

An isolation transformer is a helluvalot less expensive than a trip to the emergency room or a funeral.

 

[dougy83]

It's not as if "non-isolated" power supplies are dangerous if you don't touch any of the internals. Just put the circuit in an isolating box. LED light bulbs, hair dryers, kettles, toasters, etc. don't use transformers to isolate the power but are considered safe for use by normal people.

 

[ronv]

I don't have an isolation transformer so I try to be really careful when I work on those little non isolated supplies. It's the floating scope (and probes) that is hard to remember.
Must have fixed a thousand of those little radios as a kid in the tv shop. Never saw one where the screws were hot, but I did see some where the volume control knob was broken and the pot was hot. They would get you almost every time because a lot of them didn't have keyed plugs either. TVs were the same. They were really bad because you had to get them on the bench looking for the temperature sensitive cap that was making it roll.

 

[rc3po]

My answer is WHY??!!! Transformers are usually not that expensive and they are very easy to troubleshoot.

 

[tvtech]

My answer is WHY??!!! Transformers are usually not that expensive and they are very easy to troubleshoot.

Hi

Any Transformer that is going to fit into an enclosure (see Avatar) that is :L=100mm, W=60mm,H=30mm will have to be SMPS in order for there to be any space left for the battery, electronics and so on. As a TV tech that deals with SMPS repairs every day of my working life......I wanted to stay away from any SMPS type circuitry.

I needed extreme electrical reliability with the circuitry having to handle periodic Mains surges of anything up to 300VAC + that kills SMPS's stone dead. (Think small generators on farms that have been known to "run away" and blow up everything until they can be switched off, or our notoriously bad electricity supply in rural areas and townships/squatter camps here that causes anything SMPS to eventually fail or blow up). I needed something that could handle this kind of electrical abuse without any drama.

So in 2009 I started investigating the X2 capacitor to see how it would handle the job as a Mains current limiter. I needed 120mA constant current at a regulated 10VDC which would take care of both charging the battery and powering the LED's.

One VERY important lesson I learned whilst using a cap in this way is NEVER LOOSE THE LOAD. If for some or other reason this happens you are going to have a lot of drama on your plate. The supply voltage from the cap will go sky high and destroy your project and possibly shock you too if you are poking your fingers around inside when it happens. (This happened in the development phase where I was using breadboard...and a wire going to the head (load) came loose. The Electrolytic smoothing cap exploded and the Regulator went to heaven etc). I never got physically shocked but I was still shocked at how quickly all blew up in front of me.

So, learning from this, I decided to put everything on a PCB. The only way I could accommodate everything safely was the board had to be double sided.

So, I designed the first double sided board always keeping in mind creepage distances etc. To cut a long story short, everything worked as expected with the first prototype boards. No nasty surprises.

But as any of you know that has designed or built anything from scratch.....fine tuning is very important.

So the board went through two revisions. Little things here and little things there. One of the parts built into the last revision is a 5W Zener that clamps the output from the Bridge and in so doing aids the series Regulator in staying a bit cooler when overload times come.

So, on the 9th and 10th of June last year 2013, with this little guy in it's ABS casing and 3mm Polycarbonate lens and a small hole drilled to accommodate the heat sensor onto the Regulator and sealed from prying fingers....it was put to the test.

I initially wanted to see if it could handle 400VAC for 30 seconds. I would of been happy with that. So the test began at 400VAC...

30 Seconds came and 30 Seconds went. No problem. I said to my friend "lets try 1 Minute and see what happens". No problem.
Lets try 2 Minutes. No problem.

Ended up a in a 5 Minute run at 400VAC. All good.

So being the kind of person I am and wanting to prove that all my hard work in this was worth the while I said " we are going to do another run @ 400VAC for 5 Minutes". Same result. No problems.

And then the final run @ 400VAC 5 Minutes later while this baby is still recovering. Same result. All OK. This is my personal unit that is exactly the same as the other testing units out there....and still to this day has shown no signs of the abuse I put it through last year in June.

So lets look at stuff here:

1. I agree that Transformerless power supplies can be dangerous to people that do not understand them.
2. I agree that they are bad news for people that are merely hobbyists playing around with a potential shock hazard.
3. I agree that they are bad news for people that won't listen. And then leave in a huff.

BUT:

They are excellent for certain applications ( like mine). Will I ever release a kit that people can put together on their own = NO
Will I ever show the details of my design on a Forum or the NET = NO.
Will I encourage Newbies to try this on their own = NO.
Will I release a a fully built, tested and sealed unit....already done. I have orders. And I am not hasty for money. People that have this little Guy for testing swear by it. They find uses I never dreamed of.

All I am saying is that Transformerless power supplies are out there. Many of them. And they are crazy over the top reliable if built the correct way.

And thanks to ETO and Mods and all to get this off my chest forever

See this link here: https://www.electro-tech-online.com...he-public-domain-at-last.136196/#post-1146578

Regards
tvtech

 

[rc3po]

Hi tvtech,
Yes, transformer-less power supplies are out there. Be careful. Even experienced people can make a mistake.

 

[shortbus=]

[quote="tvtech, post: 1173838, member: 150185"

BUT:

They are excellent for certain applications ( like mine). Will I ever release a kit that people can put together on their own = NO
Will I ever show the details of my design on a Forum or the NET = NO.
Will I encourage Newbies to try this on their own = NO.
Will I release a a fully built, tested and sealed unit....already done. I have orders. And I am not hasty for money. People that have this little Guy for testing swear by it. They find uses I never dreamed of.

All I am saying is that Transformerless power supplies are out there. Many of them. And they are crazy over the top reliable if built the correct way.

And thanks to ETO and Mods and all to get this off my heart forever

See this link here: https://www.electro-tech-online.com...he-public-domain-at-last.136196/#post-1146578

Regards
tvtech[/quote]

I think you answer your own question about this, with the above quote. The people like you that can do it correctly and safely just do it. The ones that feel the need to come to an internet forum to ask "how do I do this", probably shouldn't be told how.

Will they still try? Maybe. Will they do it anyhow? Maybe. If you knew they tried (after you telling them how) and got it wrong, and hurt themselves or some one else, would you feel any responsibility? That's up to you.

As far as consumer goods having a transformer less power supply, they, the manufacturer, still needs a government sponsored testing done before it can be sold. The guy doing a first project doesn't go through this. And probably isn't going to do any kind of correct packaging of the finished project.

 

[tvtech]

Hi tvtech,
Yes, transformer-less power supplies are out there. Be careful. Even experienced people can make a mistake.

LOL

As a tvtech going on around 25 years now...highly unlikely. I respect Mains. I respect electricity. A little habit you learn over the years is just to think about things before you touch things...like what would happen if I touch "that".....

You have lots to learn.

tvtech

 

[tvtech]

Hi

I am not advocating Transformeless power supplies....All I am saying they have their time and place. And they exceed all expectations if built correctly.

That's all.

Notice there are no diagrams or instructions here....

So at least we are discussing this. Instead of forbidding it. How cool is that !!!

Thank you,
tvtech

 

[KeepItSimpleStupid]

I kinda grew up as a kid (10 years old) when things evolved. The 500 W TV's with an inherent transformer in them. Then the series filaments that made up the 120 VAC. Those 120 VAC filaments made it necessary to use an isolation transformer and I followed that by a Variac. My home made isolation transformer isn't really isolated because the ground prong is contiguous, but I don't think I ever serviced any 3 prong instrument that needed the ground isolated. The Variac was also necessary for audio amplifier troubleshooting.

Most of the early troubleshooting was done with battery operated DVM's. When you start adding a mains scope, thats when isolation is required.

So, when it came to working on 15 kV supplies that could supply 1.5 Amps and 100 kV supplies that could supply 0.1A or 1000 W RF transmitters with 3000 V plate supplies that you could not isolate, it takes a different set of rules.

Yep, I've seen the damage a a 10 uf oil filled cap charged to 300 V or so can do to a screwdriver and have personally blown up electrolytic caps by applying an AC voltage to them and I made sparks that were about 6" long with an auto ignition coil. I've gotten shocked by a lawn mower coil and probably gotten shocked by 300 VDC or so. I also got myself into a situation where I could not let go from a mains extension cord caught between my toes. I screamed. That worked. The situation was remedied with an GFCI for outdoor use. All of this happened sometime between 10 and 18 except for the lawn mower issue.

So, yea. Experienced the events first hand. At 15 KV 1.5A, there is NO ROOM for error.

Just read recently that sometimes it's a good idea to isolate just the SMPS, but keep everything else grounded if your working on the SMPS. I've only worked on a few.

So call it experience if you will. The concept of 10 mA across the heart kills and the idea of what the resistance of the human body is gives you an idea of what to look out for.
An idea of 15 KW of power gives you an idea of the destructive potential. Seeing with your own eyes the arc flash phenomenon (video or otherwise) or any other controlled experiment just reinforces that, Experiencing it first hand, just seals up the education.

You learn safety the same way. Films. The MSDS. or a group of professionals doing a Job Hazard Analysis. There is no reason why electrical safety can be taught too.

So, sometimes when changing a light bulb, you have to "suit up". Thick clothing, face shield, clean gloves. The lamp is at 15 atmospheres; can explode if installed backwards or a fingerprint is left on it. Operates at 22 V, 45 A and needs 40 k to start. Know the hazards.

Working on vacuum system, a fingerprint is a leak. A simple screw leaks unless it's vented. A vented screw has a hole down the center.

Know your opponent.

 

[tronitech]

Back in 1976 we actually built a transformerless 9V power supply as part of my apprenticeship. It was designed to physically replace the PP9 batteries often used in radios at the time.

Couldn't see it happening today!

 

[KeepItSimpleStupid]

Way back around that time period, I had a 9V battery like thing with a zip cord that plugged into an AC outlet, Never thought about if being transformerless or not. It was colored sort of a green-blue. It could be around somewhere.

The problem is that a lot of the DC adapters are not regulated enough and now I found a nice commercial rotary switch selectable voltages with a linear supply (LM317 based) that also has multiple secondaries based on the selected voltage that I use now.

 

[tvtech]

Thanks KISS for your interesting reply's

Personally, I HATE getting shocked. You should see how carefull I am when working on SMPS or TV's or a combination of both. When I was younger it was kind of funny to get belted by simply being naive...now it's not anymore @ 51 Years.

For example: If I am working on a SMPS.....first thing I do is discharge the Main Smoothing Cap.....all energy must be gone when I start working on it. Two reasons:

1. To stop me getting shocked from said cap because the SMPS was cycling and protecting itself or maybe in Standby or many other reasons that keep the cap charged up when the SMPS went faulty....when you get to work on it, it will zap you. And 400VDC makes holes in your fingers and shocks.

2. To stop myself from making things worse by soldering dry joints on a SMPS....touch the wrong part and maybe a bridge from your soldering iron = tears and start again. Was not blown and now it is.

So my love /hate relationship with SMPS continues. As far as I know, I have not seen a SMPS here ( or for that matter anywhere else ) that can do what a simple X2 Mains Cap can do. Not too much current, stable circuit, control.

And of course safety. No contact for the user with what is happening inside the box. Only Metal connection is the 220VAC supply feeding it....

And when that is pulled out....the battery takes over.

Regards,
tvtech

 

[rc3po]

LOL

As a tvtech going on around 25 years now...highly unlikely. I respect Mains. I respect electricity. A little habit you learn over the years is just to think about things before you touch things...like what would happen if I touch "that".....

You have lots to learn.

tvtech

Yes sir, I have lots to learn - and loving every minute of it!
I don't see a problem troubleshooting the TLPSU. Plugged into my Isolation Transformer would give it isolation.