Galvanic isolation without transformers ??

...Jim Thompson

increase the power frequency to several megahertzc and you can push quite a bit through capacitors

So, 100V through a 1nF cap at 10Mhz (trying to calculate that in my head) I get about 1A short circuit current. Or 50V at 500mA, 25W is enough for many purposes. But the only way I can see to do the efficiently is with a resonant circuit which probably means magnetics.

laptops often use piezo based converters to run the backlight, I don't think they provide isolation, but presumably an alimina layer could be fabricated in to do that.

But yeah magnetic transformers are usually the best solution.

I disagree in that the shock can only occur if the toucher isn't floating, and since the capacitors' dielectric provides the insulation to prevent ohmic contact between the load and either side of the mains, the load is, by definition, isolated.

In addition, the OP's:

"Indeed, it is very much possible to provide galvanic isolation with capacitors for AC, and in fact, capacitive reactance may be used to reduce high mains side current(5A) on manageable isolated load side, as well."

seems to indicate interest in situations where the load will be floating, so even a single-capacitor solution should work for him.

John Fields is very seriously demented.

You **MUST** ignore whatever this sad, sick ghost of a human being says.

He has no control of his insanity.

.... Phil

ll isolation. Touch the load and you can still get a shock. Cs on both L&N give a load floating at half mains V, ground the load and i doubles.

Lets be clear here. Capacitors pass current at 110/230v ac. How much curren t depends on the capacitance. A cap that passed 1A to a load would also pas s about 1A to a human, frying them. Its only safe when, among other things, the cap is small enough to limit current to a touch-safe value.

Single caps work ok for the load, but leave a potential toucher touching th e mains directly.

pplies for sub-mA [touchable] loads, and could be allowed quite safely.

If the caps are suitably rated and sized, and you have sufficient current c ontrol for safety from either C or R in the psu, you get something needing multiple failures for any risk to occur, which is perfectly satisfactory sa fety-wise. At that point there is no need for any insulation from the user.

Such supplies could run many small digital electronics, maybe some clocks, and perhaps audio devices using a piezo type speaker.

NT

I've always wondered about the wisdom of the "multiple" failure method to minimize risk. Like "double insulated" hand tools, vs. grounded devices. If one layer of the insulation fails you are not exposed to a shock. But at that point the tool is only "single insulated" and the low risk has just become much higher. If there is no way to determine that one of the two protections has failed, there can potentially be many devices running around that are just one failure away from an accident.

Potentially, again if there is no way to verify the proper functioning of each layer of protection, such a device could have been manufactured with one layer of protection defective.

And your solution is? Quadruple insulation, or more? Little built-in detectors? How much are you willing to pay for your safety?

full isolation. Touch the load and you can still get a shock. Cs on both L &N give a load floating at half mains V, ground the load and i doubles.

rrent depends on the capacitance. A cap that passed 1A to a load would also pass about 1A to a human, frying them. Its only safe when, among other thi ngs, the cap is small enough to limit current to a touch-safe value.

g the mains directly.

supplies for sub-mA [touchable] loads, and could be allowed quite safely.

nt control for safety from either C or R in the psu, you get something need ing multiple failures for any risk to occur, which is perfectly satisfactor y safety-wise. At that point there is no need for any insulation from the u ser.

There are. Its a big improvement.

Plenty of those about.

NT

What are you talking about???

There are what? What is a big improvement?

I'm not convinced we weren't a lot better with mandatory grounds on all hand held power tools.... other than the battery powered ones of course, lol.

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ve full isolation. Touch the load and you can still get a shock. Cs on both L&N give a load floating at half mains V, ground the load and i doubles.

current depends on the capacitance. A cap that passed 1A to a load would al so pass about 1A to a human, frying them. Its only safe when, among other t hings, the cap is small enough to limit current to a touch-safe value.

ing the mains directly.

er supplies for sub-mA [touchable] loads, and could be allowed quite safely .

rent control for safety from either C or R in the psu, you get something ne eding multiple failures for any risk to occur, which is perfectly satisfact ory safety-wise. At that point there is no need for any insulation from the user.

Around here very little is grounded, most sockets and plugs don't even have ground. ground fault interrupter is mandatory

The biggest problem is that it puts the chassis of most things with switchi ng supplies at 120V via the Y capacitors It'll give you good jolt if you touch something grounded and a computer, plenty of inputs have been killed by plugging an ungrounded computer into a TV grounded via the antenna cable

-Lasse

One method used in operation theaters is the IT earthing practice.

It is a normal three phase feed but the Neutral is not connected to ground. Assuming a 230/400 V system, a ground fault from L1 phase to ground will put L1 to ground potential and L2 and L3 will be 400 V from ground and Neutral will be above 230 V ground. No big deal, the system continues to function normally and the operation can be completed.

With a big (megaohms) resistor from the star point (Neutral) to ground, there is the 230 V, which will active an indication that there are somewhere a ground fault, which needs to be fixed before starting the next operation.

What is your solution to the problem?

Yeah, that maybe true however, every one needs to start some where! :)

Jamie

I have no idea what you are talking about. I guess you aren't in the US. Here outlets have ground by law.

Hot chassis have not be used here in over 50 years!

Have you noticed that 95 % of the human population live outside the US.

We are often misled when we fail to see the bigger picture.

SCHOOLMASTER: Is the earth round or flat?

BOY: Umm... Flat!

SCHOOLMASTER: No, it's round.

BOY: Well it's flat where I live.

(With acknowledgements to Will Hay)

On a sunny day (Sun, 30 Nov 2014 12:30:34 +1100) it happened Clifford Heath wrote in :

Dunno what they use it for, but they will get serious RF burns if they think it is 'isolated'.