Transformerless High Voltage PSU

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Asmith96

Joined May 14, 2020
5
Hi everyone, I have an idea for a High voltage PSU that uses voltage direct from the mains without a transformer but I doubt its safety. If it were used it would most likely be in an audio valve circuit to provide about 330VDC to the plates.

halfwave.png

A 6.3V transformer would be used to power the heater filaments on AC and the input signal would be decoupled from DC (in the case of a fault) using a line level 1:1 audio transformer driven by an op amp. The live and neutral are on a completely separate circuit to the safety earth which would be connected to an aluminium chassis.

I can't find any examples similar to this design so I'm wondering if its safe practice?
 

ronsimpson

Joined Oct 7, 2019
684
I have worked on radios that had a power supply like this. All the knobs and switches have plastic insulators. If the case gets broken and you touch any metal it is not good. If the know is broken do not touch the metal shaft. These radios were before three prong plugs. About 50% of the time the metal case (inside the plastic case) was connected to the hot power line.
[plastic = bakelite]
I think the safety requirements is for the insulating case to be very strong, and have no holes. A person with a knife should not be able to connect to any electronics. I think some TV sets were made this way.
 

dl324

Joined Mar 30, 2015
10,758
Welcome to AAC!
I have an idea for a High voltage PSU that uses voltage direct from the mains without a transformer but I doubt its safety.
Unfortunately, your first post violates AAC's Terms Of Service agreement (which seems to be difficult to find these days). Discussion of this particular type of transformerless power supply are prohibited.
 

ericgibbs

Joined Jan 29, 2010
10,054
hi A96,
Please note AAC's revised UA's Section #7, ie: Safety & Closing of Threads.
Mod.
  • Restricted topics. The following topics are considered "out of bounds" and will result in your thread being closed without question:
    • Any kind of over-unity devices and systems
    • Devices designed to electrocute or shock another person
    • Jammers intended for actual use in other than legal academic contexts
    • Amateur/homemade rail guns and other high-energy projectile devices
  • 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.
  • Safety & Closing of Threads. While everyone is responsible for their own safety, the moderating staff, on a case by case basis, will close discussions if they get the impression that one of the members appears unwilling or unable to appreciate the risks in what they are attempting.
 

Janis59

Joined Aug 21, 2017
1,179
The load for any valve-driven amplifier (loudspeaker, antenna, induction coil etc) MAY be touched un-intentionally, thus making such construction potentially unsafe or even dangerous. Then all the unit must be encapsulated in proper isolator box to avoid touch the parts, if indeed the load all parts forever will stay inside.

The rare cases when such touching is extremely non-probable one may choose to install the differential-current-fuse-automat before the circuit, that are current practice over the nowadays in many applications like flow-through water boilers, outside at garden electric wire rolls etc as supplementary measure in addition to the earthing.

But if You would plan to set the warning light to find the "right" position for plug, let the null will always be the output null, the more dangerous idea is difficult to realize, inspite of rather good logic in that. Don`t do so.

However I wonder why Americans are so obsessed with electrocuting risks if have the so laughfully low voltage a 110 Volts?? We use the 380/220 and I have when younger had "enjoyed" that sh* on me countless times and still alive (weed are never die). But rules are rules.
 

Janis59

Joined Aug 21, 2017
1,179
By the way, when the simplicity and weight are on the bid, nowadays to make a SMPS is taking just the same time to solder Your two diodes - let wire the ferrite core, add the couple of IRF730 and IR2153. PSU is ready and all things safe.
 

Thread Starter

Asmith96

Joined May 14, 2020
5
I have worked on radios that had a power supply like this. All the knobs and switches have plastic insulators. If the case gets broken and you touch any metal it is not good. If the know is broken do not touch the metal shaft. These radios were before three prong plugs. About 50% of the time the metal case (inside the plastic case) was connected to the hot power line.
[plastic = bakelite]
I think the safety requirements is for the insulating case to be very strong, and have no holes. A person with a knife should not be able to connect to any electronics. I think some TV sets were made this way.
I know of the dangerous designs from the past such as the All American 5 (and similar designs) and there are similarities but as you said these were before the 3 prong cords. These adds two additional benefits, voltage polarity is no longer a concern and you can earth the metal enclosure you put the circuit inside.

The enclosure is completely closed off except for the valve sockets, the IEC socket, the input jack and speaker jack. The valve sockets don't present any additional danger than in normal valve equipment, the IEC is protected from stored energy in the capacitor by the reverse breakdown voltage of the rectifier diodes and the input and outputs are protected by audio transformers.
 

Thread Starter

Asmith96

Joined May 14, 2020
5
Welcome to AAC!
Unfortunately, your first post violates AAC's Terms Of Service agreement (which seems to be difficult to find these days). Discussion of this particular type of transformerless power supply are prohibited.
hi A96,
Please note AAC's revised UA's Section #7, ie: Safety & Closing of Threads.
Mod.
  • Restricted topics.The following topics are considered "out of bounds" and will result in your thread being closed without question:
    • Any kind of over-unity devices and systems
    • Devices designed to electrocute or shock another person
    • Jammers intended for actual use in other than legal academic contexts
    • Amateur/homemade rail guns and other high-energy projectile devices
  • 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.
  • Safety & Closing of Threads. While everyone is responsible for their own safety, the moderating staff, on a case by case basis, will close discussions if they get the impression that one of the members appears unwilling or unable to appreciate the risks in what they are attempting.
I apologise I didn't mean break any forum rules and I don't want to be that guy who comes off as stubourn and argumentative especially since I'm new here.

I assume your refering to
  • Devices designed to electrocute or shock another person.

But I am definitely looking to avoid that and don't see how this rules out all transformerless power supplies. This PSU is inside an earthed enclosure with the rest of the circuit where the mains and other high voltage cannot be touched.

I am pretty sure this should be safe but because I can't find anything like it including a 3 prong cord I have doubt. So I'm looking for a confirmation that the protection from the mains is substantial or for someone to tell me why this isn't the case.
 

ronsimpson

Joined Oct 7, 2019
684
the input and outputs are protected by audio transformers.
Most/all audio transformers do not have "power line" isolation. They were never designed to do that job. (they could be modified/redesigned)
The All American 5 and others have the speaker inside the box. The antenna is inside. I remember some had a external antenna screw terminal on the back. The first component is a 1nF 1kv capacitor that holds off the 60/50hz of the power line and passes the 1mhz RF signal.
1589543261788.png
Now that I said there is a capacitor I went and checked some radios. The Sylvania radio has a "2mmF 1kv" cap(s). Most of the radios have a transformer on the front end. The primary winding is made of very well insulated wire.
 

Thread Starter

Asmith96

Joined May 14, 2020
5
Most/all audio transformers do not have "power line" isolation. They were never designed to do that job. (they could be modified/redesigned)
The All American 5 and others have the speaker inside the box. The antenna is inside. I remember some had a external antenna screw terminal on the back. The first component is a 1nF 1kv capacitor that holds off the 60/50hz of the power line and passes the 1mhz RF signal.
View attachment 207236
Now that I said there is a capacitor I went and checked some radios. The Sylvania radio has a "2mmF 1kv" cap(s). Most of the radios have a transformer on the front end. The primary winding is made of very well insulated wire.
Valve output transformers are designed to isolate high DC voltages and impedance match so I don't see anything new there. The input transformer would be a 1:1 audio probably bourns with a dielectric strength of 6.5 KVDC and with a 3 prong cord I still don't see a potential for the input to have any high voltage (AC or DC) in the case of any fault.
 

dl324

Joined Mar 30, 2015
10,758
But I am definitely looking to avoid that and don't see how this rules out all transformerless power supplies.
My bad. It seems they updated the UA recently and removed the explicit ban on transformerless power supplies. As I said, it seems to be hard to find the agreement these days.
I can't find any examples similar to this design so I'm wondering if its safe practice?
Are your electrical outlets polarized and are you using a polarized plug? What type of enclosure would this be in?

The important thing is to insure that line and neutral can't be reversed, you make that a non-issue, or you add protection against reversal.
 
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Thread Starter

Asmith96

Joined May 14, 2020
5
My bad. It seems they updated the UA recently and removed the explicit ban on transformerless power supplies. As I said, it seems to be hard to find the agreement these days.
Are your electrical outlets polarized and are you using a polarized plug? What type of enclosure would this be in?

The important thing is to insure that line and neutral can't be reversed, you make that a non-issue, or you add protection against reversal.
I'm in the UK so it's polarised and so are the plugs, the enclosure would be something sturdy and made of aluminium.

Here is my last build for an example

20200404_140552.jpg
 

dl324

Joined Mar 30, 2015
10,758
I'm in the UK so it's polarised and so are the plugs, the enclosure would be something sturdy and made of aluminium.
In the US, we probably still have residential wiring that has no earth ground and has unpolarized plugs which would make this type of design unsafe. Are GFCI's required?

With no earth ground connected to the chassis, I'd consider the design to be unsafe.
 
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