"The only appliances that NEED isolation are electronic ones that have external connections to other devices. The rest can safely rely on being fully insulated or by safety grounding any external metalwork. "

Oh really. Then plug your smartphone into an unisolated charger and then the audio output to your stereo.

"As indicated by Phil its not all appliances that need to be duly isolated.. A device like an automatic dawn to dusk light switch can be safe without an isolation transformer"

Sure, but there are different standards for construction and isolation to prevent shock.

In this country we have the UL, which is actually independent but carries alot of weight. If they find that something was not UL approved and it burns your house down they got grounds for not paying the insurance claim.

What Phil said about toasters n **** is true. But you don't plug them into anything else, like your TV or stereo. plenty of times people have plugged their smartphone into my garage stereo, now if it was also plugged into a charger that did not provide isolation then the whole system becomes "hot chassis".

I remember hot chassis TVs. The had an antenna isolator and many of them, that was the only input they had. Some had video inputs that were isolated by optos. Some people put in their own earphone jacks and in some cases took their lives into their own hands. Later, Zenith came out with a kit that had a transformer and it provdeded the isolation.

In this country you can't run isolated wire in the same conduit with non-insulated wire. That means if you dig a trench to get good power out to your garage, like 220 for your compressor and welder, you cannot run phone wires, cable wires, intercom wires or even that 24 volt stuff along with it. You need a separate conduit for it. There is no way to tell if a tree root comes up and bends it and makes it short out, causing an insidious hazard. And folks, I am sure I am not the only one in the world who goes out to the garage for a smoke barefoot. There are good reasons for most of the NEC here. In fact the NEC are about the only laws that really make sense.

I agree that some things do not need to be isolated, as long as they don't plug into anything else. Now they got kitchen appliances controlled by smartphone. Now if they are wifi that is one thing, but if they connect with RJ-45 that is another.

.."Still, in the trade, the resistive AC line cord was known as a "curtain burners" because people would often coil them up in a neat little ball instead of spreading them out as the owner's manual directed. "

Now there's something I didn't know.

wrote:

---------------------------

"The only appliances that NEED isolation are electronic ones
that have external connections to other devices. The rest can
safely rely on being fully insulated or by safety grounding any
external metalwork. "


Oh really. Then plug your smartphone into an unisolated charger
and then the audio output to your stereo.


** An un-isolated phone charger would be a dangerous and highly illegal device.

I have done a Google search and find NO evidence that there are ANY on sale.

I explained the point to Mike Coon in this thread.

Up to YOU to prove they exist.



...... Phil

wrote:

-----------------------------


I have also seen a Chines made portable radio set without transformer. It was boldly written on it "transformerless AC radio" apparently the manufacturer was boasting. A guy opened it to find out what was inside and showed us this cap drop power supply so he warned the friend against possible electric shock when he touch any metal part. the friend replied there were no metal parts so its safe. Not long before that he got zapped when he forgot that the antenna was made of metal.


** The antenna only needs a low value series cap to make it safe.

Not so long ago, lots or radios and TV were "hot chassis" designs with the antennas connected via small caps or isolating baluns.

Such sets normally have no video or audio connectors.


..... Phil

Phil Allison wrote on 8/3/2017 10:03 PM:
wrote:

-----------------------------


I have also seen a Chines made portable radio set without transformer. It was boldly written on it "transformerless AC radio" apparently the manufacturer was boasting. A guy opened it to find out what was inside and showed us this cap drop power supply so he warned the friend against possible electric shock when he touch any metal part. the friend replied there were no metal parts so its safe. Not long before that he got zapped when he forgot that the antenna was made of metal.


** The antenna only needs a low value series cap to make it safe.

Not so long ago, lots or radios and TV were "hot chassis" designs with the antennas connected via small caps or isolating baluns.

Such sets normally have no video or audio connectors.

So a single failure in a cap would render the safety factor null. It
wouldn't even affect the operation of the radio, so no one would know.

--

Rick C

The trolling Prickman ****wit wrote:

-----------------------------------




I have also seen a Chines made portable radio set without transformer. It was boldly written on it "transformerless AC radio" apparently the manufacturer was boasting. A guy opened it to find out what was inside and showed us this cap drop power supply so he warned the friend against possible electric shock when he touch any metal part. the friend replied there were no metal parts so its safe. Not long before that he got zapped when he forgot that the antenna was made of metal.


** The antenna only needs a low value series cap to make it safe.

Not so long ago, lots or radios and TV were "hot chassis" designs with the antennas connected via small caps or isolating baluns.

Such sets normally have no video or audio connectors.

So a single failure in a cap would render the safety factor null. It
wouldn't even affect the operation of the radio, so no one would know.



** Same goes for any Class 2 device with a SMPS that uses a Y2 cap to supress RFI - but you are such a bull****ting ****head you have no idea what that even is.

For the benefit of others he

The caps used in hot chassis radios and TVs were all special high voltage ceramics rated for the task.




..... Phil

In article ,
says...

I have done a Google search and find NO evidence that there are ANY on
sale.

I explained the point to Mike Coon in this thread.


IIRC, you "explained" that to some people a transformer is necessarily
an iron-cored device working at mains frequency. Whereas I think if it
quacks like a duck, it's a duck (so to speak). Not a very fundamental
distinction, but thanks for the citation...

Mike.

Mike Coon wrote:

-----------------


I have done a Google search and find NO evidence that there are ANY on
sale.

I explained the point to Mike Coon in this thread.


IIRC, you "explained" that to some people a transformer is necessarily
an iron-cored device working at mains frequency. Whereas I think if it
quacks like a duck, it's a duck (so to speak).


** It has gotta walk like a duck too, you can buy gadgets that make a realistic quacking sounud. Duck hunters use them.


Not a very fundamental
distinction, but thanks for the citation...


** Just Google "transformerless PSU schem".

Most of the hits are for isolated SMPS schems.




..... Phil

On Thursday, 3 August 2017 12:35:57 UTC+1, John-Del wrote:
On Thursday, August 3, 2017 at 12:16:59 AM UTC-4, wrote:


If you really must restore some old thing to its original, unsafe and inefficient state, by all means do so. But don't come crying to me if it burns your house down. Mainly, don't fall asleep with the thing running.


If you're referring to the resistance line cord in my example, there aren't many options even if you don't care about originality (I don't). That radio in my example has 5 tubes, two IF XFRs, a gang tuner and a dynamic speaker all crammed into a 4X10 chassis pan. The plastic cabinet covers this like a glove. There's simply no room to mount a 25W resistor or mitigate the heat that it produces.

Still, in the trade, the resistive AC line cord was known as a "curtain burners" because people would often coil them up in a neat little ball instead of spreading them out as the owner's manual directed.

I do restore an occasional antique radio for my customers, and even after adding fuses and polarized line cords to them, I instruct them on the dangers of line connected metal chassis and never plug in the radio if one of the plastic knobs falls off. I also instruct them to leave all old radios unplugged when not in use and to not leave them running unattended.

The logical option with curtain burner sets is to build a separate psu to plug them into. Use a plug that can't go into any of the usual mains adaptors.


NT

On Friday, 4 August 2017 04:07:32 UTC+1, Phil Allison wrote:
The trolling Prickman ****wit wrote:

I have also seen a Chines made portable radio set without transformer. It was boldly written on it "transformerless AC radio" apparently the manufacturer was boasting. A guy opened it to find out what was inside and showed us this cap drop power supply so he warned the friend against possible electric shock when he touch any metal part. the friend replied there were no metal parts so its safe. Not long before that he got zapped when he forgot that the antenna was made of metal.


** The antenna only needs a low value series cap to make it safe.

Not so long ago, lots or radios and TV were "hot chassis" designs with the antennas connected via small caps or isolating baluns.

Such sets normally have no video or audio connectors.

So a single failure in a cap would render the safety factor null. It
wouldn't even affect the operation of the radio, so no one would know.



** Same goes for any Class 2 device with a SMPS that uses a Y2 cap to supress RFI - but you are such a bull****ting ****head you have no idea what that even is.

For the benefit of others he

The caps used in hot chassis radios and TVs were all special high voltage ceramics rated for the task.




.... Phil

I've got sets like that from pre-war onward, none of those caps are ceramic, all paper. Safer caps came later. I'm sure there were a lot of live aerials around at one time.


NT

On Sunday, August 6, 2017 at 8:38:16 AM UTC-4, wrote:
On Friday, 4 August 2017 04:07:32 UTC+1, Phil Allison wrote:
The trolling Prickman ****wit wrote:

I have also seen a Chines made portable radio set without transformer. It was boldly written on it "transformerless AC radio" apparently the manufacturer was boasting. A guy opened it to find out what was inside and showed us this cap drop power supply so he warned the friend against possible electric shock when he touch any metal part. the friend replied there were no metal parts so its safe. Not long before that he got zapped when he forgot that the antenna was made of metal.


** The antenna only needs a low value series cap to make it safe.

Not so long ago, lots or radios and TV were "hot chassis" designs with the antennas connected via small caps or isolating baluns.

Such sets normally have no video or audio connectors.

So a single failure in a cap would render the safety factor null. It
wouldn't even affect the operation of the radio, so no one would know..



** Same goes for any Class 2 device with a SMPS that uses a Y2 cap to supress RFI - but you are such a bull****ting ****head you have no idea what that even is.

For the benefit of others he

The caps used in hot chassis radios and TVs were all special high voltage ceramics rated for the task.




.... Phil

I've got sets like that from pre-war onward, none of those caps are ceramic, all paper. Safer caps came later. I'm sure there were a lot of live aerials around at one time.


NT


That's true on this side of the pond, but Phil is on the other hemisphere. For all we know they may have used ceramic caps instead of paper in live chassis.

In article ,
says...

That's true on this side of the pond, but Phil is on the other hemisphere. For all we know they may have used ceramic caps instead of paper in live chassis.

All this talk of ponds and transformers reminds me...

Years ago a colleague sold me (for a trivial sum) a Bell & Howell "Slide
Cube?" 35mm transparency projector (which I still have; model 981Q). It
was made for the US market, so I also got a 500W autotransformer to
power it from the UK mains.

This made the kit very unwieldy, so I set out to convert it for 240V.
Swapping out the 500W lamp was easy, and getting a 240V fan motor not
too tough (though fitting it into the housing was trickier). But the
optical path included an automatic focus adjustment, and the electronics
needed a low voltage supply. It turned out that this had been supplied
by a secondary winding on the fan motor, and of course my replacement
fan did not include this. So I had to shoe-horn a small mains
transformer (no readily available switch-mode supplies back then) in as
well. But it did work, and I may pluck up courage to see if it still
does!

Beware motors masquerading as transformers!

A small postscript. A yachting magazine had an article about isolation
of marina power supplies for boats, both for safety and for prevention
of galvanic corrosion of underwater parts. But they mentioned the use of
an "autotransformer". Since I owned one, I was sensitive to the fact
that this would not provide isolation and could be dangerous, so I wrote
to the magazine. I am happy to report that they published the
correction!

Mike.

wrote:

-------------------------





** Same goes for any Class 2 device with a SMPS that uses a Y2 cap to supress RFI - but you are such a bull****ting ****head you have no idea what that even is.

For the benefit of others he

The caps used in hot chassis radios and TVs were all special high voltage ceramics rated for the task.



I've got sets like that from pre-war onward, none of those caps are
.ceramic, all paper.


** Antenna safety isolation only needs caps of about 100pF = impedance of 30 ohms at 50Mhz.

The examples I saw were sets made from the late 1960s onwards, when working of a TV hire and repair business.

Never seen a 100pF paper cap.



..... Phil

On Monday, 7 August 2017 05:52:49 UTC+1, Phil Allison wrote:
tabby wrote:

** Same goes for any Class 2 device with a SMPS that uses a Y2 cap to supress RFI - but you are such a bull****ting ****head you have no idea what that even is.

For the benefit of others he

The caps used in hot chassis radios and TVs were all special high voltage ceramics rated for the task.



I've got sets like that from pre-war onward, none of those caps are
.ceramic, all paper.


** Antenna safety isolation only needs caps of about 100pF = impedance of 30 ohms at 50Mhz.

The examples I saw were sets made from the late 1960s onwards, when working of a TV hire and repair business.

Never seen a 100pF paper cap.



.... Phil

Mine are 20s - 50s. Don't know what values the caps are offhand.


NT

John-Del wrote:
On Thursday, August 3, 2017 at 12:16:59 AM UTC-4, wrote:


If you really must restore some old thing to its original, unsafe and inefficient state, by all means do so. But don't come crying to me if it burns your house down. Mainly, don't fall asleep with the thing running.


If you're referring to the resistance line cord in my example, there aren't many options even if you don't care about originality (I don't). That radio in my example has 5 tubes, two IF XFRs, a gang tuner and a dynamic speaker all crammed into a 4X10 chassis pan. The plastic cabinet covers this like a glove. There's simply no room to mount a 25W resistor or mitigate the heat that it produces.

Still, in the trade, the resistive AC line cord was known as a "curtain burners" because people would often coil them up in a neat little ball instead of spreading them out as the owner's manual directed.

I do restore an occasional antique radio for my customers, and even after adding fuses and polarized line cords to them, I instruct them on the dangers of line connected metal chassis and never plug in the radio if one of the plastic knobs falls off. I also instruct them to leave all old radios unplugged when not in use and to not leave them running unattended.


A small 'buck' configured transformer will reduce the filament
voltage without crating a lot of waste heat.


--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

On Wednesday, August 9, 2017 at 2:43:55 PM UTC-4, Michael Terrell wrote:
John-Del wrote:
On Thursday, August 3, 2017 at 12:16:59 AM UTC-4, wrote:


If you really must restore some old thing to its original, unsafe and inefficient state, by all means do so. But don't come crying to me if it burns your house down. Mainly, don't fall asleep with the thing running.


If you're referring to the resistance line cord in my example, there aren't many options even if you don't care about originality (I don't). That radio in my example has 5 tubes, two IF XFRs, a gang tuner and a dynamic speaker all crammed into a 4X10 chassis pan. The plastic cabinet covers this like a glove. There's simply no room to mount a 25W resistor or mitigate the heat that it produces.

Still, in the trade, the resistive AC line cord was known as a "curtain burners" because people would often coil them up in a neat little ball instead of spreading them out as the owner's manual directed.

I do restore an occasional antique radio for my customers, and even after adding fuses and polarized line cords to them, I instruct them on the dangers of line connected metal chassis and never plug in the radio if one of the plastic knobs falls off. I also instruct them to leave all old radios unplugged when not in use and to not leave them running unattended.


A small 'buck' configured transformer will reduce the filament
voltage without crating a lot of waste heat.



Two problems: 1) there's precious little room in the radio in question for even a small buck transformer and 2) these radios are series string and have no power transformer to buck...

John-Del wrote:
On Wednesday, August 9, 2017 at 2:43:55 PM UTC-4, Michael Terrell wrote:
John-Del wrote:
On Thursday, August 3, 2017 at 12:16:59 AM UTC-4, wrote:


If you really must restore some old thing to its original, unsafe and inefficient state, by all means do so. But don't come crying to me if it burns your house down. Mainly, don't fall asleep with the thing running.


If you're referring to the resistance line cord in my example, there aren't many options even if you don't care about originality (I don't). That radio in my example has 5 tubes, two IF XFRs, a gang tuner and a dynamic speaker all crammed into a 4X10 chassis pan. The plastic cabinet covers this like a glove. There's simply no room to mount a 25W resistor or mitigate the heat that it produces.

Still, in the trade, the resistive AC line cord was known as a "curtain burners" because people would often coil them up in a neat little ball instead of spreading them out as the owner's manual directed.

I do restore an occasional antique radio for my customers, and even after adding fuses and polarized line cords to them, I instruct them on the dangers of line connected metal chassis and never plug in the radio if one of the plastic knobs falls off. I also instruct them to leave all old radios unplugged when not in use and to not leave them running unattended.


A small 'buck' configured transformer will reduce the filament
voltage without crating a lot of waste heat.



Two problems: 1) there's precious little room in the radio in question for even a small buck transformer and 2) these radios are series string and have no power transformer to buck...

I can understand a space problem, but you don't need a power
transformer, to add a buck transformer. It is a simple autotransformer
with the secondary wired anti phase, in series with the filaments. It is
tiny, since the secondary only has to be the proper voltage, and it will
handle the filament current. I've used them for decades, on both
electronics and industrial machine tools.



--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

On Wednesday, August 9, 2017 at 4:55:41 PM UTC-4, Michael Terrell wrote:
John-Del wrote:
On Wednesday, August 9, 2017 at 2:43:55 PM UTC-4, Michael Terrell wrote:
John-Del wrote:
On Thursday, August 3, 2017 at 12:16:59 AM UTC-4, wrote:


If you really must restore some old thing to its original, unsafe and inefficient state, by all means do so. But don't come crying to me if it burns your house down. Mainly, don't fall asleep with the thing running.


If you're referring to the resistance line cord in my example, there aren't many options even if you don't care about originality (I don't). That radio in my example has 5 tubes, two IF XFRs, a gang tuner and a dynamic speaker all crammed into a 4X10 chassis pan. The plastic cabinet covers this like a glove. There's simply no room to mount a 25W resistor or mitigate the heat that it produces.

Still, in the trade, the resistive AC line cord was known as a "curtain burners" because people would often coil them up in a neat little ball instead of spreading them out as the owner's manual directed.

I do restore an occasional antique radio for my customers, and even after adding fuses and polarized line cords to them, I instruct them on the dangers of line connected metal chassis and never plug in the radio if one of the plastic knobs falls off. I also instruct them to leave all old radios unplugged when not in use and to not leave them running unattended.


A small 'buck' configured transformer will reduce the filament
voltage without crating a lot of waste heat.



Two problems: 1) there's precious little room in the radio in question for even a small buck transformer and 2) these radios are series string and have no power transformer to buck...

I can understand a space problem, but you don't need a power
transformer, to add a buck transformer. It is a simple autotransformer
with the secondary wired anti phase, in series with the filaments.


Makes sense. The only time before this that I used a buck transformer was with another transformer. Should have given that a bit more thought. Thanks.

John-Del wrote:
Michael Terrell wrote:
John-Del wrote:

Two problems: 1) there's precious little room in the radio in question for even a small buck transformer and 2) these radios are series string and have no power transformer to buck...

I can understand a space problem, but you don't need a power
transformer, to add a buck transformer. It is a simple autotransformer
with the secondary wired anti phase, in series with the filaments.


Makes sense. The only time before this that I used a buck transformer was with another transformer. Should have given that a bit more thought. Thanks.


No problem. Most people have never even heard of boost/buck
transformers.


--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)